Parallel Safety Reflux Valve | AHN42F LPG Pump DN40-150 Factory

A Parallel Safety Reflux Valve (AHN42F series) is a spring-loaded parallel safety reflux valve - an automatic overpressure protection and recirculation device specifically designed for liquid-phase reflux pipelines, especially installed at the outlet of LPG (Liquefied Petroleum Gas) station tank pumps - when the pump outlet (discharge) pressure exceeds the preset (set) pressure, the valve automatically opens and recirculates (refluxes) the excess liquid back to the storage tank or pump inlet, thereby maintaining safe operating pressure and preventing pump overpressure, pipeline rupture, seal damage, and equipment failure in liquid transfer and recirculation systems. It adopts a parallel (straight-through) valve body structure with a spring-loaded disc/plug that moves parallel to the flow axis (parallel disc-to-seat design), a PTFE soft seal (zero leakage under normal operating pressure) or 2Cr13 metal seal, DN40-150, PN1.6-10MPa, ≤300°C, flanged connection, WCB/forged steel/stainless steel body, spring-loaded automatic operation (no external power), designed for LPG, air, and various liquids - a reliable liquid reflux overpressure protection valve for pump outlet pipelines. The core highlights are: (a) Liquid-phase reflux specific design (core): (i) specifically for liquid media (LPG, gasoline, chemicals, water) - not for gas/steam (different from full-lift safety valve); (ii) reflux/recirculation function - when pump outlet pressure exceeds set, valve opens and liquid flows back to tank/inlet (recirculation), rather than discharging to atmosphere (closed-loop protection); (iii) parallel (straight-through) flow path - low flow resistance, smooth liquid recirculation, minimal pressure drop when open; (iv) modulating/proportional opening - opens gradually with overpressure (liquid systems need stable recirculation, not rapid pop); (b) Spring-loaded automatic operation: (i) spring force holds disc closed at normal pressure; (ii) when pump outlet pressure × disc area > spring force, disc lifts - valve opens; (iii) opening proportional to overpressure (more pressure = more opening = more reflux); (iv) when pressure drops to reseat, spring closes - automatic, no external power/actuator; (v) set pressure adjustable via adjusting screw; (c) PTFE soft seal zero leakage: (i) PTFE (polytetrafluoroethylene) sealing surface on disc - chemical inert, low friction, excellent sealing; (ii) zero leakage under normal operating pressure (bubble-tight, Class VI) - prevents LPG/liquid loss and fugitive emission; (iii) PTFE resists LPG, gasoline, oils, many chemicals; (iv) optional 2Cr13 (13Cr stainless) metal seal for higher temp/wear; (d) LPG station pump outlet protection (primary application): (i) LPG station tank pumps - when downstream valve closes or demand drops, pump deadheads (pressure spikes); (ii) reflux valve opens, recirculates LPG back to tank - prevents pump overpressure, seal failure, pipeline burst; (iii) mandatory for LPG station pump protection (per LPG station codes); (iv) also for gasoline/diesel pump stations, chemical transfer pumps, water pump recirculation; (e) Small bore, medium-low pressure: (i) DN40-150 (1.5"-6") - typical pump outlet sizes; (ii) PN1.6-10MPa (Class 150-600) - medium-low pressure liquid systems; (iii) ≤300°C - PTFE limit (2Cr13 for higher); (f) Parallel body structure: (i) straight-through (inlet and outlet in line, like globe valve body but parallel disc); (ii) compact, easy install between pump outlet and reflux line; (iii) flanged connection (ANSI/DIN/JIS/GB); (g) Materials: (i) body: WCB carbon (general LPG/oil/water), forged steel (high pressure), stainless CF8/CF8M (corrosive chemical); (ii) disc: stainless + PTFE or 2Cr13; (iii) spring: 50CrVA alloy spring steel; (iv) stem: stainless; (h) Standards/certification: ISO 9001, CE (PED), SGS; design per GB/T 12243 (safety valve), API 520 (sizing); (i) Applications: LPG stations (tank pump outlet), chemical/petrochemical (pump recirculation, distillation reflux), oil & gas (pump protection, transfer), food/pharma (fluid transfer), other (water pump, papermaking, mining); (j) Safety + cost-effective: spring-loaded = simple, reliable, no power, low cost; closed-loop reflux = no medium loss (vs atmospheric discharge). This is the reliable spring-loaded parallel safety reflux valve for liquid-phase pump outlet overpressure protection and recirculation.

The spring-loaded parallel structure, PTFE soft seal zero leakage, liquid-phase reflux/recirculation function, LPG station pump outlet specialization, small bore (DN40-150), medium-low pressure (PN1.6-10MPa), and closed-loop protection (reflux to tank, no atmospheric discharge) make this valve a specialized liquid-phase reflux safety valve - distinct from general full-lift safety valves (for gas/steam, atmospheric discharge) - designed for pump outlet overpressure protection and liquid recirculation in LPG stations, chemical/petrochemical, oil & gas, and food/pharma where automatic pump protection, zero leakage, and closed-loop recirculation are priorities. Compared to Main Safety Valve (first in relief series): (a) Main Safety Valve = full-lift, gas/steam, large discharge to atmosphere/discharge header, DN15-300, PN16-420, -29~550°C, metal Stellite hard seal, general boiler/vessel overpressure; (b) This Parallel Safety Reflux Valve = parallel modulating, liquid, reflux/recirculation to tank/inlet (closed-loop), DN40-150, PN1.6-10MPa, ≤300°C, PTFE soft seal, LPG pump outlet specific; (c) key difference: this valve recirculates liquid back to system (not discharges to atmosphere) - for pump protection where medium is valuable/hazardous (LPG) and atmospheric discharge is unsafe/wasteful; (d) another difference: this valve is modulating (gradual opening for stable recirculation) vs full-lift "pop" (rapid for gas). Working principle (detailed): (a) closed (pump outlet pressure < set): spring holds disc on PTFE seat - sealed, no reflux; pump delivers liquid downstream; (b) at set (pump outlet pressure × disc area = spring force): disc starts to lift - reflux begins; (c) open/reflux (pressure > set): disc lifts proportionally - liquid flows from pump outlet through valve back to tank/inlet (reflux line); more pressure = more opening = more recirculation; pump outlet pressure controlled; (d) reseat/close (pressure drops to reseat, 85-95% set): spring closes disc - reflux stops; (e) modulating - stable recirculation flow, no chatter (for liquid systems). Parallel vs full-lift structure: (a) parallel (this valve): disc moves parallel to flow axis (like globe valve plug), straight-through body, modulating, for liquid reflux; (b) full-lift (main safety valve): disc rotates/lifts perpendicular, huddling chamber pop action, for gas/steam discharge; (c) parallel = low flow resistance when open (good for recirculation flow). PTFE soft seal vs metal seal: (a) PTFE (standard): zero leakage (Class VI), chemical inert (LPG, oil, chemical), low friction, ≤200°C (some PTFE grades to 260°C, but typically ≤200°C for safety - page says ≤300°C with 2Cr13 option); (b) 2Cr13 (optional metal): higher temp (≤300°C+), wear resistant, but leakage (Class IV), not zero; (c) for LPG (ambient temp, hazardous), PTFE zero leakage is preferred (prevents fugitive emission). LPG station pump protection (primary use case): (a) LPG station has storage tank + pump (canned motor pump or positive displacement pump) + dispenser; (b) when dispenser closes or demand drops, pump continues running - deadhead (pump against closed valve) → pressure spikes rapidly; (c) without reflux valve, pressure can exceed pump/pipeline rating → seal failure, pipeline rupture, LPG release (fire/explosion hazard); (d) reflux valve at pump outlet opens at set pressure (e.g., 1.6MPa), recirculates LPG back to tank - pressure controlled, pump protected; (e) mandatory per LPG station design codes (e.g., GB 51142, NFPA 58 - LPG pump must have bypass/reflux valve); (f) PTFE seal = zero LPG leakage (critical - LPG is flammable, toxic, ozone-depleting). Pump types protected: (a) positive displacement pumps (gear, vane, piston) - MUST have reflux/bypass (deadhead pressure rises rapidly, can destroy pump); (b) centrifugal pumps - optional reflux (centrifugal can deadhead for short time, but reflux recommended for continuous operation); (c) canned motor pumps (LPG) - reflux for cooling/protection. Installation: (a) install on pump discharge (outlet), reflux line back to storage tank vapor space or pump inlet; (b) reflux line size ≥ valve outlet (no restriction); (c) set pressure = pump rated pressure or pipeline MAWP (whichever lower), typically 1.1-1.2× normal operating; (d) flanged connection (easy install/removal); (e) vertical or horizontal (parallel body allows any orientation, but follow manufacturer); (f) isolation valve (for maintenance, locked open during operation). Testing/certification: (1) set pressure test (bench - liquid/air, verify opens at set ±tolerance); (2) seat leakage test (PTFE = zero leakage / Class VI; 2Cr13 = API 527); (3) body hydrostatic 1.5×PN; (4) reflux flow test (verify capacity at set overpressure); (5) material cert; (6) nameplate (set pressure, capacity, medium, serial). Maintenance: (a) periodic test - annually (bench, set pressure + seal leakage); (b) inspect PTFE seal - cold flow/deformation (replace if damaged); (c) spring - fatigue (replace if set drifts); (d) clean - LPG residue, debris; (e) exercise - if pump runs continuously, valve may not operate often - test periodically; (f) do not adjust set without certification. Troubleshooting: (a) leakage at seat: PTFE cold flow/deformation (replace), foreign material (clean), operating too close to set (increase margin); (b) opens below set: spring set wrong, pump pressure spike (check pump), wrong spring; (c) does not open: disc stuck (PTFE adhered to seat after long idle - exercise), spring set too high, guide binding; (d) chatter: reflux line too small (backpressure), oversized valve, pump pressure oscillation; (e) reflux capacity insufficient: valve undersized, set too high, reflux line restricted. Important: (a) for liquid only (not gas/steam - use full-lift safety valve); (b) closed-loop reflux (not atmospheric discharge - ensure reflux line to tank/inlet); (c) PTFE ≤200°C (for >200°C use 2Cr13 or other); (d) set pressure certified (do not field-adjust); (e) mandatory for positive displacement pumps (LPG, chemical); (f) reflux line must be adequate (no restriction); (g) warranty: 18 months. The valve is manufactured under strict quality control with 100% set pressure test, 100% seat leakage test, material cert, ISO 9001/CE/SGS. With an 18-month warranty and OEM/ODM customization (size, pressure, material, set pressure, connection), this valve is a reliable spring-loaded parallel safety reflux valve for liquid-phase pump outlet overpressure protection and recirculation.

1.Liquid-Phase Reflux + Pump Overpressure Protection

Specifically designed for liquid-phase reflux pipelines - when pump outlet pressure exceeds set pressure, valve automatically opens and recirculates excess liquid back to storage tank or pump inlet (closed-loop protection), preventing pump deadhead overpressure, pipeline rupture, and seal failure. Parallel straight-through flow path with low resistance ensures smooth recirculation. Modulating/proportional opening (gradual with overpressure) for stable liquid recirculation - no rapid pop/chatter. Primary application: LPG station tank pump outlet (mandatory per LPG codes), also gasoline/diesel/chemical/water pumps.

2.Spring-Loaded Automatic + Adjustable Set Pressure

Spring-loaded direct-acting mechanism - 50CrVA alloy spring holds disc closed; when liquid pressure × disc area exceeds spring force, disc lifts and reflux begins; recloses automatically when pressure drops to reseat (85-95% set). No external power/actuator needed - self-actuated, reliable, low cost. Set pressure adjustable via bonnet adjusting screw (clockwise = higher set, counterclockwise = lower), locked with locknut and sealed cap - must be verified by bench test and set by authorized shop.

3.PTFE Soft Seal Zero Leakage

High-quality PTFE (polytetrafluoroethylene) sealing surface on disc - chemical inert, low friction, excellent sealing, achieves zero leakage (Class VI bubble-tight) under normal operating pressure. Prevents LPG/liquid loss and fugitive emission (critical for flammable/toxic LPG). PTFE resists LPG, gasoline, oils, many chemicals, ≤200°C. Optional 2Cr13 (13Cr stainless) metal seal for higher temperature (≤300°C) and wear applications - Class IV leakage. Precision-machined seat/disc for tight shutoff.

4.Small Bore + Medium-Low Pressure + Durable Materials

DN40-DN150 (1.5"-6") - typical pump outlet sizes; PN1.6-10MPa (Class 150-600) - medium-low pressure liquid systems; ≤300°C (with 2Cr13; PTFE ≤200°C). Body: carbon steel WCB (general LPG/oil/water), forged steel (high pressure), stainless steel CF8/CF8M (corrosive chemical). Disc: stainless + PTFE or 2Cr13. Spring: 50CrVA alloy spring steel (shot peened, fatigue resistant). Stem: stainless. Handles LPG, air, gasoline, diesel, chemicals, water, various liquids.

5.Parallel Body + Flanged Connection + Easy Maintenance

Parallel (straight-through) valve body structure - inlet and outlet in line, compact, low flow resistance, easy installation between pump outlet and reflux line. Flanged connection (ANSI B16.5/DIN/JIS/GB RF) - easy install/removal for maintenance. Simple structure with fewer parts - routine maintenance only requires inspection, cleaning, and PTFE seal/spring replacement; no complex actuator. Detachable bonnet for internal access. Reduces downtime and maintenance cost.

6.Standards + Quality + Warranty + Versatile

ISO 9001 certified, CE (PED optional), SGS inspection available. Design per GB/T 12243, API 520 (sizing). 100% set pressure bench test, 100% seat leakage test (PTFE zero leakage / 2Cr13 API 527), 100% body hydrostatic (1.5×PN), material cert, nameplate (set pressure, capacity, medium, serial). For LPG stations, chemical/petrochemical, oil & gas, food/pharma, water pump, papermaking, mining. 18-month warranty, OEM/ODM customization (DN, PN, material, set pressure, connection, seal material).

A Parallel Safety Reflux Valve (AHN42F) operates on the principle of spring force vs. liquid pressure force equilibrium in a spring-loaded parallel (straight-through) valve body - the spring (50CrVA, compressed via adjusting screw) exerts a downward closing force on the disc/plug (with PTFE or 2Cr13 seal) through the stem, holding the disc tightly against the seat in the parallel (straight-through) body (closed, sealed) when pump outlet pressure is below the set pressure; when the pump outlet liquid pressure rises to the set pressure, the upward force (liquid pressure × disc area) equals the spring force, and the disc starts to lift (parallel to flow axis); as pressure increases further (overpressure), the disc lifts proportionally (modulating) - opening a flow path from inlet (pump outlet) through the valve body to outlet (reflux line back to tank/inlet), recirculating the excess liquid back to the storage tank or pump suction, which limits/controls the pump outlet pressure; when the pump outlet pressure drops to the reseating pressure (typically 85-95% of set), the spring force again exceeds the liquid pressure force, pushing the disc back onto the seat - the valve closes automatically and reseals (PTFE zero leakage), stopping reflux and returning to standby; the set pressure is adjustable by turning the adjusting screw (clockwise compresses spring = higher set, counterclockwise = lower set), then locked with a locknut and sealed cap - but adjustment must be verified by bench test and done by authorized personnel. The valve consists of a parallel (straight-through) body (WCB/forged/stainless, with inlet from pump outlet and outlet to reflux line), a disc/plug (stainless with PTFE or 2Cr13 sealing surface, moves parallel to flow axis), a seat (PTFE or 2Cr13, matched to disc), a stem (stainless, connects disc to spring), a spring (50CrVA, provides closing force), a bonnet (encloses spring/stem, with adjusting screw), an adjusting screw + locknut (sets spring compression = set pressure), a cap (protects adjustment, sealed), and flanged ends (ANSI/DIN/JIS/GB). Closed state (normal pump operation, P < set): (a) spring force (F_spring) > liquid pressure force (P_liquid × A_disc); (b) disc pressed tightly against seat - PTFE seal, zero leakage (Class VI); (c) no reflux; (d) pump delivers liquid downstream normally (valve is closed, not in flow path). At set pressure (P_liquid × A_disc = F_spring): (a) equilibrium - disc starts to lift (first "crack"); (b) reflux begins (small flow from pump outlet to reflux line); (c) for liquid (incompressible), opening is modulating/gradual (no pop - unlike gas full-lift safety valve). Open/reflux state (P > set, overpressure): (a) disc lifts proportionally to overpressure - more pressure = more lift = more reflux flow; (b) liquid flows: pump outlet → valve inlet → past disc → valve outlet → reflux line → storage tank (or pump inlet); (c) recirculation - excess liquid is returned to system (closed-loop, not atmospheric discharge); (d) pump outlet pressure is controlled/limited (cannot rise above set + accumulation); (e) modulating provides stable recirculation (no chatter - important for liquid systems); (f) valve remains open as long as pressure > reseat. Reseat/close state (P drops to reseat): (a) when P_liquid × A_disc < F_spring (at reseat pressure, typically 85-95% of set); (b) spring pushes disc back onto seat; (c) valve closes, PTFE reseals (zero leakage); (d) blowdown = set pressure - reseat pressure (typically 5-15% of set); (e) after reseat, reflux stops, pump returns to normal delivery. Set pressure adjustment: (a) remove cap (break seal), loosen locknut; (b) turn adjusting screw: (i) clockwise → compresses spring more → higher set pressure; (ii) counterclockwise → releases spring → lower set pressure; (c) tighten locknut, reinstall cap, reseal; (d) must verify set pressure by bench test (liquid/air) after adjustment; (e) field adjustment by unauthorized personnel prohibited (safety-critical for pump protection). Parallel (straight-through) structure: (a) inlet and outlet are in line (straight-through flow path, like a globe valve body but with parallel-moving disc); (b) disc moves parallel to flow axis (vertical to seat, which is perpendicular to flow); (c) low flow resistance when open (smooth straight-through path, minimal turbulence - good for recirculation flow); (d) compact, easy to install in pump outlet + reflux line; (e) vs angle body: parallel = straight-through (lower resistance, easier piping) vs angle = 90° turn (more resistance, but some applications). PTFE soft seal principle: (a) PTFE (Teflon) disc seal - soft, compliant material; (b) when closed, spring force compresses PTFE against seat - PTFE deforms slightly to fill microscopic gaps → zero leakage (bubble-tight, Class VI); (c) PTFE is chemical inert - resists LPG, gasoline, oils, acids, solvents (pH 0-14); (d) PTFE has low friction - disc opens/closes smoothly, low torque; (e) temperature limit: PTFE ≤200°C (above, PTFE softens/cold flows - seal degrades); (f) for >200°C, use 2Cr13 (13Cr stainless) metal seal (hard, wear resistant, ≤300°C+, but leakage Class IV, not zero). LPG pump protection (primary application - detailed): (a) LPG station setup: storage tank (liquid LPG, ~0.5-1.5MPa vapor pressure) → pump (canned motor pump, positive displacement) → dispenser → vehicle; (b) normal operation: pump draws LPG from tank, delivers to dispenser at ~1.6-2.5MPa; (c) overpressure scenario: when dispenser nozzle closes (vehicle tank full) or demand drops, pump continues running → deadhead (pump against closed downstream) → pressure rises rapidly (positive displacement pump can generate very high pressure, 2-3× normal); (d) without reflux valve: pressure exceeds pump/pipeline rating → pump seal failure, pipeline rupture, LPG release → fire/explosion hazard; (e) with reflux valve: installed at pump outlet, set at e.g. 1.6MPa → when pressure reaches 1.6MPa, valve opens → LPG recirculates back to tank → pressure controlled at ≤1.6MPa + accumulation → pump protected; (f) mandatory per LPG codes (GB 51142 LPG station code, NFPA 58 - LPG pump must have bypass/reflux valve sized for pump capacity); (g) PTFE zero leakage = no LPG fugitive emission (critical - LPG is flammable, heavier than air, explosive in confined spaces). Pump types: (a) positive displacement pumps (gear, vane, piston, screw) - MUST have reflux/bypass valve (deadhead pressure rises rapidly, can destroy pump/pipeline); (b) centrifugal pumps - optional (centrifugal can deadhead for short time, but continuous deadhead causes overheating; reflux recommended for continuous operation or high-value liquid); (c) canned motor pumps (LPG, toxic) - reflux for cooling (recirculated liquid cools motor) + pressure protection. Reflux line design: (a) reflux line size ≥ valve outlet (no restriction - restriction causes backpressure, reduces reflux capacity, causes chatter); (b) reflux to tank vapor space (not liquid space - prevents liquid hammer, allows vapor disengagement) or to pump inlet (suction); (c) reflux line slope to tank (no liquid trap); (d) no check valve in reflux line (would block reflux); (e) isolation valve (for maintenance, locked open during operation). Set pressure selection: (a) set pressure ≤ pump rated pressure (pump mechanical seal/pressure rating); (b) set pressure ≤ pipeline MAWP; (c) set pressure > normal operating pressure (at least 10-20% above - prevents simmering/leakage); (d) typical LPG pump: set = 1.1-1.2× pump normal discharge pressure; (e) set pressure marked on nameplate (bar/psi). Capacity (reflux flow): (a) valve must have reflux capacity ≥ pump rated capacity (when fully closed downstream, all pump flow must go through reflux); (b) capacity depends on orifice/disc size, set pressure, overpressure, liquid density/viscosity; (c) size valve per pump capacity (not pipe size); (d) we provide capacity tables/sizing. Testing: (1) body hydrostatic 1.5×PN; (2) set pressure test (bench - liquid/air, verify opens at set ±tolerance); (3) seat leakage test - PTFE: zero leakage (bubble test at 90% set); 2Cr13: API 527; (4) reflux flow/capacity test (verify flow at set overpressure); (5) material cert; (6) nameplate (set pressure, capacity, medium, serial). Installation: (a) location: pump discharge (outlet), as close to pump as possible; (b) orientation: parallel body allows horizontal or vertical (follow manufacturer - typically any); (c) inlet: full bore, short, no restrictions; (d) outlet (reflux): to tank vapor space or pump inlet, adequate size, no check valve; (e) flanged connection (gasket, torque cross-pattern); (f) isolation valve (for maintenance, locked open + car sealed during operation); (g) set pressure ≤ pump/pipeline rating. Maintenance: (a) periodic bench test - annually (set pressure + seat leakage); (b) inspect PTFE seal - cold flow, deformation, cuts (replace if damaged); (c) spring - fatigue (replace if set drifts >5%); (d) clean - LPG residue, scale, debris; (e) exercise valve - if pump runs continuously with stable demand, valve may not operate for months - test periodically (manual lift or pump deadhead test); (f) replace gaskets when removed; (g) records - test dates, set pressure, parts. Troubleshooting: (a) seat leakage (weeping): (i) PTFE cold flow/deformation (replace PTFE disc/seat); (ii) foreign material (clean); (iii) operating pressure too close to set (>90% set - valve simmers, increase set margin); (iv) spring weak (replace); (b) opens below set: (i) spring set too low (readjust); (ii) pump pressure spike (check pump - relief valve, pressure regulator); (iii) wrong spring (replace); (c) does not open / stuck: (i) disc stuck (PTFE adhered to seat after long idle at high temp - exercise/replace PTFE); (ii) spring set too high (readjust); (iii) guide/stem binding (align/lubricate); (iv) foreign material jamming (clean); (d) chatter (rapid cycling): (i) reflux line too small/restricted (backpressure - enlarge line); (ii) oversized valve (too much capacity for pump - rapid pressure drop); (iii) pump pressure oscillation (check pump); (iv) blowdown too low (reseats too quickly); (e) insufficient reflux capacity: (i) valve undersized (replace larger); (ii) set too high (opens too late); (iii) reflux line restricted (clear/enlarge); (f) PTFE damage: (i) over-temperature (>200°C - use 2Cr13); (ii) foreign material (clean); (iii) cold flow (replace with higher-grade PTFE or 2Cr13). Important: (a) for liquid only (not gas/steam - use full-lift safety valve for gas/steam); (b) closed-loop reflux (must connect reflux line to tank/inlet - do not discharge to atmosphere, especially LPG); (c) PTFE ≤200°C (for >200°C use 2Cr13 metal seal); (d) set pressure certified (do not field-adjust without authorization); (e) mandatory for positive displacement pumps (LPG, chemical transfer); (f) reflux line must be adequate (no restriction, to tank vapor space); (g) size per pump capacity (not pipe size); (h) warranty: 18 months; (i) codes: GB/T 12243, API 520, LPG station codes (GB 51142, NFPA 58). With proper sizing (per pump capacity), installation (pump outlet, adequate reflux line), and periodic testing, this parallel safety reflux valve provides reliable automatic liquid recirculation and overpressure protection for pump outlet pipelines.

• LPG + LNG + Fuel Gas Stations

LPG (Liquefied Petroleum Gas) station tank pump outlet - mandatory reflux/recirculation valve for positive displacement LPG pumps (canned motor pumps), prevents pump deadhead overpressure when dispensers close, recirculates LPG back to storage tank. Also LNG pump skids, gasoline/diesel fuel stations, compressed natural gas (CNG) stations. PTFE zero leakage prevents flammable LPG fugitive emission. Set pressure matched to pump rating (typically 1.6-2.5MPa). DN40-150, flanged. Reliable for LPG/fuel gas station pump overpressure protection.

• Chemical + Petrochemical Industry

Chemical transfer pumps (gear/vane/piston for solvents, acids, caustic, monomers), petrochemical refinery pump recirculation lines, distillation column reflux, reactor feed pump protection. Reflux valve protects positive displacement pumps from deadhead overpressure, recirculates chemical back to tank/inlet. Stainless CF8/CF8M body for corrosive chemicals, PTFE seal for chemical resistance. Closed-loop recirculation prevents hazardous chemical release to atmosphere. For acids, solvents, polymers, petrochemical intermediates. Reliable for chemical/petrochemical pump protection.

• Oil + Gas + Petroleum Industry

Oil pipeline transfer pumps, crude oil tank farm pumps, produced water pumps, fuel oil transfer, hydraulic systems. Reflux valve protects pumps from overpressure during blocked discharge or demand fluctuation, recirculates oil/water back to tank. WCB body for oil/water, PTFE or 2Cr13 seal. Medium-low pressure PN1.6-10MPa. Also for oilfield chemical injection pumps, well test separators. Reliable for oil & gas pump overpressure protection and recirculation.

• Food + Pharmaceutical Industry

Food-grade liquid transfer pumps (beverage, dairy, syrup, edible oil), pharmaceutical fluid transfer (solvents, APIs, WFI water), CIP (Clean-in-Place) system pumps. Reflux valve protects pumps and maintains pressure stability, PTFE seal is FDA-compliant (food-grade PTFE optional), stainless steel body for hygiene/corrosion. Zero leakage prevents product contamination/loss. For food processing, pharmaceutical manufacturing, biotech. Reliable for food/pharma fluid transfer pump protection.

• Water + Other Industries

Water treatment high-pressure pumps, boiler feedwater recirculation, cooling water pumps, papermaking stock pumps, mining slurry pumps (with 2Cr13 wear seal), power plant auxiliary pumps, municipal water supply, HVAC. Reflux valve protects centrifugal/positive displacement pumps from overpressure, recirculates water/liquid back to reservoir. WCB/stainless body, PTFE or 2Cr13 seal. DN40-150, PN1.6-10MPa. 18-month warranty, OEM/ODM (set pressure, material, size). Reliable for water and general industrial pump overpressure protection.

Our Parallel Safety Reflux Valves are manufactured under an ISO 9001:2015 certified quality management system, with every valve undergoing rigorous inspection and testing at each production stage - because these valves are safety-critical pump protection devices used for LPG station pumps (flammable/explosive), chemical transfer pumps (corrosive/toxic), oil pumps, food/pharma pumps where set pressure drift, PTFE seal leakage, spring fatigue, body burst, or reflux capacity insufficiency can cause pump failure, pipeline rupture, LPG/chemical release, fire/explosion, and safety incidents (the PTFE seal quality, spring set pressure accuracy, and reflux capacity are critical additional quality points).

Raw material control: every body/disc/stem/spring material batch comes with material certificate (chemical + mechanical per heat); carbon steel WCB verified; forged steel verified (A105, high pressure); stainless CF8/CF8M (304/316) verified; PTFE verified (molecular weight, density, purity - food-grade optional, FDA compliance); 2Cr13 (13Cr) verified; spring 50CrVA verified (chemical, tensile, fatigue); fasteners verified.

Body manufacturing: (a) casting (WCB/CF8/CF8M) or forging (forged steel, high-pressure small bore); (b) heat treatment (normalizing/tempering, solution annealing for stainless); (c) 100% visual; (d) NDT - radiographic/ultrasonic of body (for PN6.4+ and forged, 100% for PN10); (e) wall thickness (per standard - critical for pressure); (f) parallel body machining - inlet/outlet flanges, seat recess, stem bore, bonnet; (g) flange machining (RF); (h) chemical/mechanical/hardness per heat; (i) surface treatment - paint (blue) or high-temp paint; (j) nameplate (stainless, engraved - set pressure, capacity, medium, serial).

Disc/seat manufacturing: (a) PTFE seal: (i) PTFE sheet/rod (virgin or filled PTFE, food-grade optional); (ii) machined to disc seal profile; (iii) dimensional check, surface finish (no defects); (iv) cold flow resistance test (sample - compression set); (v) bonded or mechanically retained on stainless disc; (b) 2Cr13 metal seal: (i) 2Cr13 (13Cr stainless) ring/disc; (ii) heat treatment (hardness HRC 28-32); (iii) precision grinding + lapping (matched seat); (c) disc stainless body, machined, PTFE/2Cr13 attached.

Spring manufacturing: (a) 50CrVA alloy spring steel, hot/cold coiled; (b) shot peened (fatigue resistance); (c) stress relieved; (d) set pressure test - compress to set, verify force (spring rate); (e) fatigue test (sample - 100,000 cycles, no fracture/set drift).

Stem/guides: (a) stem stainless (304/316/410), machined; (b) guides stainless/bronze (anti-galling).

Assembly: (1) install seat; (2) install disc + stem + guides; (3) install spring + bonnet + adjusting screw; (4) set spring compression to target set pressure (preliminary); (5) install cap + seal; (6) bench test set pressure (adjust to exact set).

Pressure/testing - 100% every valve: (1) body hydrostatic shell 1.5×PN - no leak; (2) set pressure test (bench) - (i) liquid test (water/oil) or air test: apply pressure, record pressure at first lift/crack - must be set ±tolerance (±3% or ±0.015MPa); (ii) adjust if needed; (3) seat leakage test: (i) PTFE: apply liquid/air at 90% set, zero visible leakage (bubble-tight, Class VI) - no bubbles; (ii) 2Cr13: API 527 (bubble count); (4) reflux flow/capacity test (sample or 100% for critical) - verify flow rate at set + 10% overpressure; (5) operation/reseat test - verify smooth opening, reseat at 85-95% set, no chatter; (6) material cert; (7) nameplate. Set pressure accuracy (critical): (a) tolerance ±3% (set ≥0.3MPa) or ±0.015MPa (set <0.3MPa); (b) we test every valve with liquid/air and adjust to exact set; (c) spring range - each spring covers a set range; correct spring selected; (d) temperature correction (for high temp, PTFE/2Cr13); (e) set pressure marked on nameplate (bar/psi).

PTFE seal quality: (a) virgin PTFE (not regrind) - better sealing, less cold flow; (b) filled PTFE (glass/carbon filled) optional - higher wear resistance, less cold flow (but slightly less chemical resistance); (c) food-grade PTFE (FDA 21 CFR 177.1550) for food/pharma; (d) compression set test (sample - ≤10% at 200°C); (e) zero leakage verified (100% bubble test). Traceability system: (a) unique serial number on nameplate; (b) database links: raw material cert (including PTFE cert, spring cert), heat number, casting/forging batch, NDT report, hydrostatic test, set pressure test report (actual set, tolerance), seat leakage report (zero/API 527), spring batch, production date, inspector, set pressure, size, customer/order; (c) full batch traceability.

Coating & marking: exterior - epoxy/polyester powder (blue) or high-temp paint; interior - bare (media contact); valve permanently marked with: set pressure (bar/psi), reflux capacity (m³/h or L/min at set+10%), medium (LPG/liquid), standard, body material, seal material (PTFE/2Cr13), serial number, year, manufacturer; nameplate (stainless, engraved, tamper-resistant); lead/wire seal on adjusting cap.

Documentation: shipped with set pressure test report, seat leakage report, material certificate (body, spring, PTFE), traceability ID, installation/operation/maintenance manual (including pump protection, reflux line design, set pressure adjustment, maintenance), and CE/PED cert (if required).

Warranty: 18 months from shipment or 12 months from installation (valve body + spring + disc/seat); wear/consumable parts (PTFE seal cold flow, gasket, spring fatigue beyond rated) - normal wear not covered; extended warranty and third-party inspection (BV, SGS, TUV), CE/PED, food-grade FDA available. Safety-critical quality commitment: (a) no valve ships without 100% set pressure + seat leakage test; (b) PTFE zero leakage verified (for PTFE type); (c) set pressure certified and sealed; (d) reflux capacity verified (sample or 100%); (e) material traceable; (f) spring fatigue tested (sample); (g) nameplate accurate (set, capacity, medium - safety-critical); (h) installation manual included (pump outlet, reflux line to tank, no check valve).

Q: How is this parallel safety reflux valve different from a main safety valve?

A: The Parallel Safety Reflux Valve (AHN42F) and the Main Safety Valve (spring-loaded full-lift) are both spring-loaded overpressure protection valves, but they are designed for different media, functions, and applications. Here's the detailed comparison. Core function difference: (a) Main Safety Valve (full-lift): overpressure protection by discharging excess medium to atmosphere or a discharge header (open-loop) - when pressure exceeds set, valve opens, medium is released/discharged (to atmosphere, flare, or header), pressure drops; (b) Parallel Safety Reflux Valve: overpressure protection by recirculating (refluxing) excess liquid back to the storage tank or pump inlet (closed-loop) - when pump outlet pressure exceeds set, valve opens, liquid flows back to tank/inlet, pressure drops; medium is NOT discharged to atmosphere. Medium difference: (a) Main Safety Valve: primarily for gas, steam, vapor (compressible media) - full-lift pop action, large discharge capacity; can be used for liquid (derated); (b) Parallel Safety Reflux Valve: specifically for liquid (LPG, gasoline, chemicals, water) - modulating action, reflux/recirculation; NOT for gas/steam. Structure difference: (a) Main Safety Valve: full-lift - disc lifts 25-30% of nozzle diameter, huddling chamber creates rapid "pop" action for gas/steam; (b) Parallel Safety Reflux Valve: parallel (straight-through) - disc moves parallel to flow axis (like globe plug), modulating/gradual opening (no pop), straight-through flow path for smooth liquid recirculation. Seal difference: (a) Main Safety Valve: metal hard seal (Stellite) - for high temp (to 550°C), wear, but leakage Class IV (not zero); (b) Parallel Safety Reflux Valve: PTFE soft seal (standard) - zero leakage (Class VI), chemical inert, for LPG/liquid, ≤200°C; optional 2Cr13 metal seal (≤300°C, Class IV). Size/pressure/temp difference: (a) Main Safety Valve: DN15-300, PN16-420 (Class 150-2500), -29~550°C (wide, high pressure, high temp, cryogenic option); (b) Parallel Safety Reflux Valve: DN40-150, PN1.6-10MPa (Class 150-600), ≤300°C (smaller, medium-low pressure, lower temp). Application difference: (a) Main Safety Valve: boilers (steam), pressure vessels (air/gas storage), petrochemical reactors, power plant steam, natural gas transmission - general overpressure protection for gas/steam; (b) Parallel Safety Reflux Valve: LPG station tank pump outlet (primary), chemical transfer pumps, oil pumps, water pumps - pump outlet overpressure protection + liquid recirculation. Discharge/reflux destination: (a) Main Safety Valve: outlet to atmosphere, flare stack, or discharge header (medium is released - for steam, may discharge to atmosphere; for gas, to flare/header); (b) Parallel Safety Reflux Valve: outlet to storage tank vapor space or pump inlet (medium is recirculated - closed-loop, no release; especially important for LPG which is flammable/valuable - atmospheric discharge is unsafe/wasteful). Action type: (a) Main Safety Valve: rapid pop (for gas/steam - quick response to fast pressure rise); (b) Parallel Safety Reflux Valve: modulating/proportional (gradual opening for stable liquid recirculation - no chatter). When to use which: (a) Use Parallel Safety Reflux Valve if: (i) medium is liquid (LPG, gasoline, chemical, water); (ii) need pump outlet protection (positive displacement pump deadhead); (iii) want closed-loop recirculation (no atmospheric discharge - valuable/hazardous liquid); (iv) small/medium pump outlet (DN40-150, PN1.6-10); (v) need zero leakage (PTFE, for LPG/hazardous); (b) Use Main Safety Valve if: (i) medium is gas/steam/vapor; (ii) need large discharge capacity to atmosphere/header; (iii) boiler/pressure vessel protection (not pump); (iv) wide size/pressure/temp (DN15-300, PN16-420, 550°C); (v) metal hard seal for high temp. Can a main safety valve be used for liquid reflux? (a) technically yes (full-lift safety valve can be used for liquid with derated capacity), but: (i) full-lift pop action may cause water hammer in liquid; (ii) discharging liquid to atmosphere is wasteful/hazardous (LPG); (iii) PTFE seal not standard on main safety valve (metal seal = leakage); (iv) parallel reflux valve is purpose-built for liquid pump recirculation (better); (b) for LPG pump, parallel safety reflux valve is the correct choice (not main safety valve). Can a parallel reflux valve be used for gas? (a) not recommended - (i) parallel modulating design doesn't have huddling chamber/pop action for gas; (ii) gas needs large discharge capacity (parallel valve capacity may be insufficient); (iii) PTFE seal for gas may have permeation; (b) use main safety valve (full-lift) for gas/steam. Summary table: | Dimension | Parallel Safety Reflux Valve | Main Safety Valve (Full-Lift) 

Important: (a) this valve = liquid reflux/pump protection (not gas/steam safety); (b) main safety valve = gas/steam overpressure discharge (not liquid reflux); (c) for LPG station pump, use this parallel reflux valve (mandatory per codes); (d) for boiler steam, use main safety valve (ASME I); (e) we manufacture both - tell us your medium/application, we recommend. This valve (AHN42F) = spring-loaded parallel safety reflux valve for liquid-phase pump outlet overpressure protection + recirculation (closed-loop), PTFE zero leakage, DN40-150, PN1.6-10MPa - specifically for LPG/chemical/oil/water pumps, distinct from main safety valve (gas/steam full-lift discharge).

Q: How do I size and set the reflux valve for my LPG pump?

A: Sizing and setting a parallel safety reflux valve for an LPG (or any liquid) pump requires matching the valve's reflux capacity to the pump rated capacity and setting the pressure at the correct level - this is safety-critical (undersized = pump overpressure, oversized = chatter). Here's the step-by-step guide. 1. Determine pump rated capacity (most critical for sizing): (a) get the pump nameplate/curve - rated flow (Q_pump, in m³/h, L/min, or GPM) at rated pressure; (b) the reflux valve must have reflux capacity ≥ pump rated capacity (when downstream is fully closed, ALL pump flow must go through reflux valve - otherwise pressure continues to rise); (c) add margin (10-20% above pump rated - for pump wear, voltage variation, viscosity changes); (d) required reflux capacity = Q_pump × 1.1~1.2; (e) example: LPG pump rated 10 m³/h → valve capacity ≥ 11-12 m³/h. 2. Determine set pressure: (a) set pressure ≤ pump rated pressure (pump mechanical seal, casing pressure rating - pump nameplate); (b) set pressure ≤ pipeline/reflux line MAWP; (c) set pressure > normal operating pressure (at least 10-20% above - prevents simmering/PTFE leakage at normal operating); (d) typical LPG pump: normal discharge 1.0-1.5MPa, set = 1.6MPa (1.1-1.6× normal, ≤ pump rated 2.5MPa); (e) set pressure = pump relief setting (if pump has built-in relief, set valve at same or slightly lower); (f) mark set pressure on nameplate (bar/psi); (g) accumulation: when valve opens, pressure may rise 5-10% above set (modulating) - ensure set + accumulation ≤ pump/pipeline rating. 3. Select valve size (DN) by reflux capacity: (a) each valve size (DN40-150) has a reflux capacity curve/table (flow at set + 10% overpressure, for liquid density/viscosity); (b) select valve where rated reflux capacity ≥ required capacity (from step 1); (c) do not base on pipe size (pump outlet may be DN50 but valve may need DN80 for capacity); (d) do not oversize (too much capacity → rapid pressure drop → chatter; valve should operate at 70-90% of rated capacity); (e) we provide capacity tables - give us pump flow + set pressure + liquid density/viscosity, we size. 4. Select seal material: (a) PTFE (standard): for LPG, gasoline, oils, chemicals, ≤200°C, zero leakage required - recommended for LPG; (b) 2Cr13 metal: for >200°C, wear (slurry), or where PTFE not compatible (some solvents at high temp) - Class IV leakage; (c) food-grade PTFE (FDA): for food/pharma; (d) LPG at ambient temp → PTFE (zero leakage, chemical inert). 5. Select body material: (a) WCB carbon steel: general LPG, oil, water (most common); (b) stainless CF8/CF8M: corrosive chemicals (acids, caustic, solvents); (c) forged steel: high pressure (PN6.4-10MPa); (d) LPG (non-corrosive) → WCB (cost-effective). 6. Reflux line design (critical for proper operation): (a) reflux line size ≥ valve outlet size (no restriction - restriction causes backpressure, reduces capacity, chatter); (b) reflux destination: (i) storage tank vapor space (preferred - liquid enters vapor space, allows flash vapor to disengage, prevents liquid hammer); (ii) pump inlet (suction line) (acceptable - recirculates to pump suction); (iii) NOT to atmosphere (LPG - unsafe/illegal); (c) no check valve in reflux line (would block reflux); (d) no isolation valve during operation (if installed for maintenance, must be locked open + car sealed); (e) reflux line slope toward tank (no liquid trap); (f) reflux line length as short as practical (minimize friction loss); (g) backpressure at valve outlet must be ≤10% of set (if more, valve set shifts - but this valve is conventional spring, so account for backpressure or use bellows type if high backpressure - typically reflux to tank has low backpressure). 7. Installation: (a) location: as close to pump discharge (outlet) as possible (between pump and first isolation valve); (b) orientation: parallel body - horizontal or vertical (follow manual, typically any); (c) inlet: full bore, short, no restrictions; (d) outlet: to tank vapor space/pump inlet (as above); (e) flanged - gasket (spiral wound or PTFE for LPG), torque cross-pattern; (f) set pressure verified by factory (do not field-adjust). 8. Testing/commissioning: (a) pre-startup: verify valve set pressure (nameplate vs spec), verify reflux line connected to tank, no check valve, isolation valve open; (b) startup: start pump, slowly close downstream valve (simulate deadhead), monitor pump outlet pressure - verify valve opens at set pressure, pressure stabilizes (doesn't exceed set + accumulation), reflux flow to tank; (c) leak check: soap solution at valve body/flange/reflux line (no LPG leak); (d) record: set pressure, stable pressure during reflux, date. Common mistakes: (a) basing valve size on pipe size (undersized/oversized - must base on pump capacity); (b) set pressure too high (above pump rating - pump damaged before valve opens); (c) set pressure too close to operating (valve simmers/leaks at normal - PTFE weeps); (d) reflux line too small (backpressure, reduced capacity, chatter); (e) reflux to liquid space (liquid hammer - should be vapor space); (f) check valve in reflux line (blocks reflux - dangerous); (g) using main safety valve for LPG pump (wrong type - pop action + atmospheric discharge); (h) no margin on capacity (valve exactly at pump rated - pump wear/voltage may exceed capacity). What we need from you to size: (a) pump make/model, rated flow (m³/h or L/min), rated pressure (bar/psi), pump type (positive displacement/centrifugal/canned motor); (b) medium (LPG? gasoline? chemical? water? density, viscosity, temp); (c) normal operating pressure; (d) pipeline/reflux line size and MAWP; (e) desired set pressure (or we recommend); (f) connection standard (ANSI/DIN/JIS/GB); (g) we provide sizing + valve selection + set pressure. Important: (a) reflux valve sizing = engineering - must match pump capacity; (b) set pressure ≤ pump/pipeline rating, ≥1.1× operating; (c) reflux line to tank vapor space, no check valve, adequate size; (d) we can help size - provide pump details; (e) set pressure is factory-set and certified (do not field-adjust); (f) for positive displacement pumps, reflux valve is mandatory (code requirement). This valve = DN40-150, PN1.6-10MPa, reflux capacity per size - provide your pump flow/pressure/medium, we size and set per your LPG/liquid pump.

Q: PTFE vs 2Cr13 seal - which do I need, and what is the temperature limit?

A: This valve offers two seal options: PTFE (polytetrafluoroethylene, soft seal) as standard, and 2Cr13 (13Cr stainless steel, metal seal) as optional. The choice depends on your medium temperature, chemical compatibility, wear, and leakage requirement. PTFE soft seal (standard): (a) Material: PTFE (Teflon) - virgin or filled (glass/carbon), food-grade optional; (b) Sealing performance: zero leakage (Class VI bubble-tight) - PTFE is soft/compliant, deforms to fill microscopic gaps, excellent shutoff; (c) Chemical resistance: excellent - inert to almost all chemicals: LPG, gasoline, oils, acids (sulfuric, hydrochloric), caustic (NaOH), solvents, salts, pH 0-14; (d) Friction: low friction coefficient - disc opens/closes smoothly, low operating force; (e) Temperature limit: ≤200°C (standard PTFE; some filled PTFE to 260°C, but for safety valve, recommend ≤200°C - above, PTFE softens, cold flows, seal degrades/leaks); (f) Wear resistance: moderate - PTFE can cold flow (permanent deformation) under high pressure/temp, can be scratched by foreign particles; (g) Cost: lower than metal seal; (h) Best for: LPG, gasoline, diesel, oils, chemicals, water, food/pharma, ambient/moderate temp (≤200°C), where zero leakage is required (hazardous/valuable liquid). 2Cr13 metal seal (optional): (a) Material: 2Cr13 (13Cr martensitic stainless steel, equivalent to AISI 420) - heat treated, hardness HRC 28-32; (b) Sealing performance: Class IV leakage (low leakage, not zero - metal-to-metal seal always has microscopic gaps); (c) Chemical resistance: good - resists water, steam, oils, mild chemicals; less resistant than PTFE to strong acids/caustic (can corrode); (d) Temperature limit: ≤300°C (or higher with proper material - metal seal handles high temp); (e) Wear resistance: excellent - hard metal, resists abrasion (slurry, particles), no cold flow; (f) Cost: higher (precision grinding/lapping required); (g) Best for: high temperature (>200°C), abrasive media (slurry, particles), steam/hot oil, where zero leakage not required and metal durability needed. Selection guide: (a) LPG (ambient temp, flammable): PTFE (zero leakage prevents fugitive emission - critical; LPG is flammable/explosive; ambient temp well within PTFE limit); (b) Gasoline/diesel/fuel oil (ambient/moderate): PTFE (zero leakage, chemical resistant); (c) Chemicals (acids, caustic, solvents, ≤200°C): PTFE (excellent chemical resistance, zero leakage); (d) Water (ambient/hot ≤200°C): PTFE (zero leakage, low cost); (e) Food/pharma: food-grade PTFE (FDA) (hygiene, zero leakage, chemical inert); (f) Hot oil/thermal fluid (>200°C): 2Cr13 (PTFE would fail above 200°C); (g) Steam (>200°C): 2Cr13 (but note: this valve is for liquid, not steam main - use main safety valve for steam); (h) Slurry/abrasive liquid (particles): 2Cr13 (PTFE scratches easily); (i) High temperature chemical (>200°C): 2Cr13 (or special alloy - consult); (j) Zero leakage required + ≤200°C: PTFE; (k) High temp/wear + leakage acceptable: 2Cr13. Temperature effect on PTFE: (a) ≤100°C: PTFE excellent (no cold flow, zero leakage); (b) 100-200°C: PTFE good (some cold flow possible under high pressure - use filled PTFE or higher spring force); (c) >200°C: PTFE softens significantly, cold flows, seal degrades → do not use PTFE (switch to 2Cr13); (d) < -20°C: PTFE becomes brittle (can crack) → for cryogenic, use special low-temp PTFE or 2Cr13 (this valve not for cryogenic - use cryogenic safety valve). PTFE types: (a) Virgin PTFE: best chemical resistance, best sealing, but more cold flow (for general LPG/chemical); (b) Glass-filled PTFE (25% glass): less cold flow, higher wear resistance, slightly lower chemical resistance (glass can be attacked by HF/strong alkali - for general oil/water); (c) Carbon-filled PTFE: better wear, thermal conductivity, for high pressure; (d) Food-grade PTFE: FDA 21 CFR 177.1550 compliant (for food/pharma); (e) specify if you need filled/food-grade. 2Cr13 details: (a) 2Cr13 = Chinese grade (0.2% C, 13% Cr), equivalent to AISI 420; (b) heat treated (quench + temper) to HRC 28-32; (c) sealing surfaces precision ground + lapped (matched disc/seat for Class IV); (d) for higher temp/wear, can use Stellite (Co-Cr) overlay (ask - more expensive); (e) 2Cr13 can corrode in strong acids (use 316 or Stellite for corrosive + high temp). Leakage comparison: (a) PTFE: zero visible bubbles (bubble test at 90% set, Class VI) - no medium loss; (b) 2Cr13: API 527 Class IV (e.g., ≤40 bubbles/min for metal seat, depends on size) - small leakage acceptable for non-hazardous high-temp liquid; (c) for LPG/hazardous, zero leakage (PTFE) is strongly preferred (even small LPG leak = fire/explosion risk). Common mistakes: (a) using PTFE at >200°C (seal fails, leaks); (b) using 2Cr13 for LPG (leakage = hazardous - should be PTFE zero leakage); (c) using virgin PTFE for high pressure (cold flow - use filled PTFE); (d) using 2Cr13 for strong acid (corrodes - use PTFE or special alloy); (e) not considering temp (PTEE limit is critical). Important: (a) standard = PTFE (for LPG/liquid ≤200°C, zero leakage); (b) optional = 2Cr13 (for >200°C or abrasive); (c) tell us your medium + max temperature - we recommend seal; (d) PTFE ≤200°C (hard limit - do not exceed); (e) for LPG, PTFE is mandatory (zero leakage, code/safety); (f) we can provide filled PTFE, food-grade PTFE, or Stellite overlay on request. This valve = PTFE soft seal (standard, zero leakage, ≤200°C, LPG/chemical/oil/water) or 2Cr13 metal seal (optional, ≤300°C, high-temp/wear) - specify your medium and temperature, we recommend.

Q: Can I adjust the set pressure in the field, and how do I test the valve?

A: Set pressure adjustment in the field is generally prohibited (must be done by authorized/certified personnel with bench test verification), but periodic testing (bench test and operational test) is required for safety. Here's the detailed guide. Can I adjust set pressure in the field? (a) Generally NO - set pressure is a safety-critical parameter, must be: (i) set and tested at factory/certified shop (bench test); (ii) sealed with lead/wire seal on cap (prevents unauthorized adjustment); (iii) marked on nameplate (certified value); (b) Why prohibited: (i) wrong set pressure = valve opens too late (pump/pipeline overpressure) or too early (nuisance reflux, product loss); (ii) field adjustment without test = guessing (can't verify accurately without bench); (iii) code/insurance (LPG station codes, ASME/API) require certified set pressure and sealed adjustment; (iv) voids warranty/certification if unauthorized; (c) If adjustment is necessary (e.g., pump changed, process modified): (i) must be done by authorized/certified valve technician; (ii) remove valve from line, take to bench test facility (or use portable test rig); (iii) break cap seal, loosen locknut, turn adjusting screw (clockwise = higher set, counterclockwise = lower); (iv) verify with bench test (liquid/air pressure gauge, record first lift - must be new set ±tolerance); (v) retighten locknut, reinstall cap, apply new seal (lead/wire); (vi) update nameplate/records (new set pressure, date, technician, certifying body); (vii) reinstall valve; (d) Never adjust without test verification (guessing is dangerous); (e) If set pressure needs to change outside current spring range: replace spring (different range) - must be done by factory/shop. Testing schedule: (a) LPG station pump reflux valve: (i) operational test: annually (or per LPG station inspection - some require every 6 months) - during pump deadhead test, verify valve opens at set, pressure stabilizes; (ii) bench test: every 1-3 years (remove valve, test set pressure + seat leakage on bench - per insurer/code); (iii) visual/leak check: monthly (soap solution for LPG leak at valve body/flange/reflux line); (b) Chemical/oil/water pump: (i) bench test: annually (or per plant maintenance); (ii) operational test: during planned pump deadhead (if safe); (c) After any overpressure event (valve discharged): inspect/test as soon as possible (verify reseat, leakage, no damage); (d) After fire/incident: replace or full overhaul + test. Bench test procedure (authorized shop): (a) remove valve from line (isolate, depressurize, drain liquid); (b) mount on test bench (liquid/air supply, precision pressure gauge ±0.5%, counter/flow meter); (c) set pressure test: (i) slowly increase inlet pressure (liquid or air), record pressure at first lift/crack (audible/visible flow or pressure drop); (ii) must be within ±3% (or ±0.015MPa) of marked set; (iii) if out of tolerance, adjust (see above) or replace spring; (d) seat leakage test: (i) PTFE: apply pressure at 90% of set, close outlet, observe for bubbles/leakage - must be zero (no visible bubbles for 1 minute); (ii) 2Cr13: API 527 (bubble count at 90% set, ≤limit); (e) reflux capacity test (if required): apply set + 10% pressure, measure flow rate (L/min or m³/h) - verify ≥ rated capacity; (f) reseat/blowdown: slowly decrease pressure, record reseat pressure, calculate blowdown (set - reseat, should be 5-15%); (g) reassemble, reset, reseal, update records. Field operational test (without removing valve): (a) LPG pump deadhead test (annual, by qualified technician): (i) ensure safe conditions (ventilation, no ignition, PPE); (ii) start pump, slowly close downstream valve (or use bypass) to simulate deadhead; (iii) monitor pump outlet pressure - verify valve opens at set pressure (pressure gauge), pressure stabilizes (doesn't exceed set + 10%), reflux flow to tank (listen/feel for flow in reflux line); (iv) slowly open downstream, verify valve closes (pressure returns to normal, no leakage); (v) record: set pressure observed, max pressure, date, technician; (b) leak check: soap solution at valve body, bonnet, flange connections, reflux line - no bubbles (LPG leak); (c) visual inspection: cap seal intact, nameplate legible, no corrosion/damage, reflux line clear; (d) do not test by manually lifting if valve has no lever (this valve typically no lever - use pump deadhead). Maintenance during bench test: (a) inspect PTFE seal: (i) if cold flow/deformation/cuts - replace PTFE disc/seat; (ii) clean (LPG residue, debris); (b) inspect spring: (i) check for fracture, corrosion, set drift (if set drifted >5%, replace spring); (ii) clean; (c) inspect guides/stem: galling, wear - lubricate (anti-seize); (d) replace gaskets (body/bonnet, flange) - always new; (e) clean internal (scale, rust, debris); (f) verify nameplate (legible, set matches). Signs valve needs service: (a) visible leakage at seat (weeping LPG/liquid when closed); (b) valve opens below set (spring weak/set wrong - pump pressure spikes earlier); (c) valve does not open / stuck (disc galled, PTFE adhered, guide binding - pump overpressure risk); (d) chatter (rapid cycling during reflux - reflux line issue or oversized); (e) corrosion/damage visible; (f) past due test date; (g) cap seal broken (possible unauthorized adjustment - retest immediately). Records (safety-critical): (a) maintain valve log: tag number, location (pump ID), set pressure, capacity, last test date, next test due, test results (set, leakage, capacity), parts replaced, technician, cap seal number; (b) LPG station inspector/insurer may require records; (c) nameplate must remain legible; (d) cap seal intact (no unauthorized adjustment). Common mistakes: (a) field-adjusting set pressure without bench test (dangerous, illegal); (b) not testing annually (valve sticks, leaks, fails when needed); (c) ignoring seat leakage (PTFE weeping = LPG leak, fire hazard); (d) breaking cap seal and not resealing (unauthorized adjustment risk); (e) no records (can't prove compliance); (f) testing pump deadhead without safety precautions (LPG - fire/explosion risk). Important: (a) set pressure = certified shop only (do not field-adjust without authorization + bench test); (b) test annually (bench), operational test (pump deadhead) for LPG; (c) replace wear parts (PTFE, spring, gaskets) as needed; (d) keep records (safety-critical, LPG code); (e) we offer bench test service, spare parts, recertification; (f) warranty: 18 months, but proper testing/maintenance required. This valve = set pressure factory-certified and sealed (no unauthorized field adjustment), requires annual bench test (set pressure + PTFE zero leakage) and periodic operational test (pump deadhead for LPG) - follow code/insurer schedule, keep records, use authorized technicians.

Q: What backpressure can this valve handle, and does it need a bellows?

A: This parallel safety reflux valve is a conventional spring-loaded valve (no bellows as standard) - its set pressure is affected by outlet backpressure. Understanding backpressure is critical for proper operation. What is backpressure? (a) backpressure = pressure at the valve outlet (reflux line side) when valve is closed or discharging; (b) superimposed backpressure: static pressure in reflux line when valve is closed (e.g., tank vapor pressure, pressure from other reflux valves in common header); (c) built-up backpressure: pressure that develops when valve discharges (dynamic, from flow through reflux line - friction, elevation); (d) total backpressure = superimposed + built-up. Effect on conventional spring valve (this valve): (a) backpressure at outlet acts on top of disc/bonnet side → adds to spring force → increases effective set pressure (valve opens at higher pressure than marked); (b) formula (simplified): effective_set = marked_set + backpressure × (disc_area - stem_area)/disc_area ≈ marked_set + backpressure (for large disc); (c) if superimposed backpressure is constant (e.g., reflux to fixed-pressure tank at 0.5MPa), you can compensate by setting valve lower (marked_set = desired_set - backpressure); (d) if backpressure is variable (built-up during discharge, or tank pressure changes), cannot compensate → set pressure varies, valve may chatter or open at wrong pressure; (e) rule: conventional valve OK if superimposed backpressure ≤10% of set (negligible effect). Typical reflux valve backpressure (LPG pump): (a) reflux to storage tank vapor space: backpressure = tank vapor pressure (LPG tank at ambient = 0.5-1.0MPa, depending on temp); (b) if set pressure = 1.6MPa, tank vapor = 0.8MPa → backpressure = 0.8MPa = 50% of set → significant effect (effective set = 1.6 + 0.8 = 2.4MPa - valve opens too late!); (c) this is a common issue - must account for tank vapor backpressure; (d) compensation: set valve at desired_effective - backpressure = 1.6 - 0.8 = 0.8MPa marked → effective = 0.8 + 0.8 = 1.6MPa (correct); (e) but if tank vapor pressure varies with temperature (LPG vapor pressure changes 0.5MPa summer vs 0.3MPa winter), backpressure varies → set varies → may need bellows or accept seasonal adjustment. When do you need bellows? (a) superimposed backpressure >10% of set (constant, but large - like LPG tank 50%); (b) variable backpressure (tank pressure changes with temp, common header with other valves); (c) corrosive/toxic medium (LPG, chemicals - backpressure medium would reach spring/bonnet, cause corrosion/fugitive emission through bonnet vent); (d) precision set pressure required (cannot tolerate set shift); (e) if any of above, use bellows-balanced safety reflux valve (bellows separates bonnet from outlet, set independent of backpressure). Does this valve have bellows option? (a) standard AHN42F = no bellows (conventional); (b) we can offer bellows version (AHN42F with 316L/Inconel bellows) on request - for high/variable backpressure or corrosive/toxic media; (c) bellows version = set pressure independent of backpressure, protects spring/bonnet, prevents fugitive emission; (d) bellows has cycle life (100,000+) - inspect periodically. How to handle backpressure for LPG reflux (practical): (a) Option 1 - Conventional valve + set compensation (most common for LPG): (i) calculate tank vapor pressure at max ambient temp (worst case); (ii) set valve at desired_effective - max_backpressure (marked set lower); (iii) accept that at lower temp (lower backpressure), effective set is slightly lower (still safe - opens earlier, nuisance reflux possible but not dangerous); (iv) simple, low cost; (b) Option 2 - Bellows valve: (i) set = desired (no compensation needed); (ii) works regardless of tank pressure variation; (iii) more expensive, bellows maintenance; (c) Option 3 - Reflux to pump inlet (suction): (i) backpressure = pump suction pressure (lower, more stable than tank vapor); (ii) less backpressure effect; (iii) but pump suction may have NPSH issues (hot LPG flashing); (d) consult LPG station code/designer for best approach. Built-up backpressure (during discharge): (a) when valve opens, reflux flow through line creates friction pressure; (b) if reflux line is too small/long/restricted, built-up backpressure is high → reduces effective capacity, causes chatter; (c) reflux line must be sized (≥ valve outlet, short, no restrictions) to keep built-up backpressure ≤10% of set; (d) we can calculate built-up backpressure if you provide line size/length/fittings. Backpressure limit summary: (a) conventional (this valve): superimposed backpressure ≤10% set (without compensation); with compensation, constant backpressure up to ~50% set (but variable not recommended); (b) bellows version: any backpressure (set independent); (c) built-up backpressure: ≤10% set (reflux line design); (d) if in doubt, use bellows or consult factory. How to verify backpressure effect: (a) calculate: backpressure = tank vapor pressure (at max temp) + built-up (flow friction); (b) measure: install pressure gauge at valve outlet (reflux line) when pump is running and valve closed; (c) if backpressure >10% set and variable → consider bellows; (d) if backpressure constant → compensate set pressure. Common mistakes: (a) ignoring tank vapor backpressure (LPG - set too high, valve opens late, pump overpressure); (b) reflux line too small (high built-up backpressure, chatter, reduced capacity); (c) using conventional valve with variable backpressure (set drifts); (d) reflux to tank liquid space (backpressure + liquid hammer); (e) not accounting for seasonal temp variation (LPG vapor pressure changes). Important: (a) this valve = conventional (no bellows standard) - set affected by backpressure; (b) for LPG reflux to tank, account for tank vapor backpressure (compensate set or use bellows); (c) reflux line must be adequate (minimize built-up backpressure); (d) if backpressure >10% set or variable/corrosive, ask for bellows version; (e) tell us your reflux destination (tank/inlet), tank pressure, reflux line size - we calculate backpressure and recommend conventional or bellows; (f) we offer bellows option on this valve series. This valve = conventional spring-loaded (set affected by backpressure, ≤10% without compensation; constant backpressure compensable; bellows version available for >10% or variable/corrosive) - specify your reflux destination and backpressure, we recommend configuration and set pressure.

Q: What is the warranty, and what does it cover (reflux valve specific)?

A: Warranty period: (a) Valve (body, disc, seat, stem, spring, bonnet): 18 months from shipment date (or 12 months from installation date, whichever comes first); (b) wear/consumable parts (PTFE seal cold flow/deformation, 2Cr13 wear, gasket, spring fatigue beyond rated, packing) - not covered under normal wear; (c) set pressure accuracy - warranted at time of shipment (tested); drift due to improper maintenance/adjustment/backpressure not covered; (d) reflux capacity - warranted per certified test (if NB/certified). What is covered: (a) body defects - casting/forging defects (porosity, cracks, wrong material), wall thickness; (b) spring defects - manufacturing defect, premature fatigue (within rated cycle life), wrong spring rate; (c) PTFE seal - manufacturing defect (wrong material, defects, bond failure) - not normal cold flow/wear from high temp/particles; (d) 2Cr13 seat/disc - manufacturing defect (wrong hardness, delamination); (e) set pressure - out of tolerance at shipment (we test to ±3%); (f) guides/stem - manufacturing defect (galling due to wrong material/alignment); (g) nameplate - wrong info (we correct). What is NOT covered: (a) normal wear - PTFE cold flow/deformation (from high temp/pressure), seat wear from particles, spring fatigue after rated cycles, gasket degradation; (b) improper installation - wrong orientation, reflux line too small (causes chatter), backpressure not accounted (set shift), no pipe support, wrong gasket, reflux to wrong destination; (c) improper operation - medium outside rated temp (PTFE >200°C), pressure beyond rating, using for gas/steam (not liquid), water hammer from improper reflux; (d) unauthorized adjustment - field set pressure adjustment without certification, broken cap seal, modified internals; (e) lack of maintenance - no periodic test (valve sticks, PTFE adheres), corrosion from neglect, foreign material damage; (f) accident/damage - fire, freezing, impact, pump runaway overpressure; (g) wrong application - using for gas/steam (should use main safety valve), using PTFE for >200°C, using conventional valve with high backpressure without compensation; (h) consequential damages - downtime, product loss (LPG), pump damage, equipment damage, injury (safety valve is protection device - proper sizing/installation/maintenance is user responsibility). Safety-critical notes: (a) warranty ≠ safety guarantee - reflux valve must be properly sized (pump capacity), installed (pump outlet, adequate reflux line), tested, maintained to function; (b) set pressure must be recertified periodically (annual bench test); (c) capacity must be verified for your pump (we can size, but user provides accurate pump data); (d) code compliance - user responsible for LPG station codes (GB 51142, NFPA 58) in their jurisdiction; (e) do not use valve beyond rated conditions; (f) reflux valve is pump protection - not substitute for pump pressure regulator or proper pump control. Warranty claim process: (a) notify us within 30 days of discovering defect (email: Contact@thankfulmaterial.com, phone: +86-15094398934); (b) provide evidence: photos/videos, valve nameplate (set pressure, capacity, serial, date), tag/location, pump details (type, flow, pressure), medium, operating conditions (temp, pressure, backpressure), maintenance records (last test, set history), failure description (leak, won't open, chatter); (c) we evaluate - may request return for bench test/inspection (small valve), or on-site; (d) remedy: repair (send parts/technician), replacement (valve/parts), refund; (e) timeline: 7-30 days (safety-critical - prioritize). Extended warranty / service options: (a) extended warranty 24/36 months - +10-20%; (b) spare parts kit (PTFE disc/seat, spring, gasket, 2Cr13 option) - recommended for LPG stations; (c) bench test service - we can test/recertify your valves (send to us); (d) on-site service - engineer visit (optional, paid); (e) annual maintenance contract - scheduled testing/parts (for LPG stations/multi-pump plants); (f) emergency replacement - stock valves for fast delivery. Spare parts availability: (a) PTFE disc/seat (matched set, virgin/filled/food-grade) - 10+ years; (b) 2Cr13 disc/seat - 10+ years; (c) spring (50CrVA, various ranges) - 10+ years; (d) gaskets (body/bonnet, flange - spiral wound/PTFE for LPG); (e) guides/stem (stainless/bronze); (f) cap/locknut/seal wire; (g) provide valve serial number/tag for correct parts. Important warranty notes: (a) 18 months from shipment (not from when put in service - unless installation date documented and within 12 months); (b) keep records - installation date, test dates, set pressure, pump data, maintenance (helps with claims and LPG compliance); (c) material cert + test reports - keep; (d) don't exceed ratings (PN/temp/medium - voids warranty, dangerous; PTFE >200°C = seal failure); (e) genuine parts - use our spare parts (non-genuine voids); (f) authorized adjustment - set pressure by certified shop only; (g) LPG safety-critical - even under warranty, user must maintain/test (neglect is not covered). This valve = 18-month valve warranty (body/spring/trim), wear parts (PTFE, gaskets) not covered, set pressure certified at shipment, extended warranty/spare parts/bench test service available - proper sizing (pump capacity), installation (reflux line to tank, backpressure accounted), annual testing, and authorized adjustment are required for safety function and warranty validity. Note: Always operate within rated pressure (≤PN, set pressure certified), temperature (PTFE ≤200°C, 2Cr13 ≤300°C), and medium (liquid only - LPG/oil/chemical/water, not gas/steam), install at pump outlet with adequate reflux line to tank vapor space (no check valve), account for backpressure, test annually (bench) and periodically (pump deadhead for LPG), do not field-adjust set pressure without authorization - this ensures reliable pump overpressure protection and maintains warranty validity.

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