China Dual Plate Check Valve Factory & Exporter

Swing check valves utilize a single large disc that swings freely on a top hinge pin. Because the disc travel angle is large (typically 70° to 85°), it takes a comparatively long time to shut when forward flow slows down. When pump failure occurs, reverse fluid velocity accelerates back through the valve before the heavy disc reaches its seat, causing massive dynamic water hammer slamming, high noise, and structural pipeline damage. In contrast, a dual plate check valve divides the disc into two semicircular plates hinged around a central pin. The travel distance is reduced by more than 50%, and calibrated torsion springs provide immediate mechanical closing torque. The plates close precisely at zero velocity before reverse flow can initiate, providing silent, non-slam operation while reducing valve weight by up to 80%.

Yes. Dual plate check valves can be mounted in vertical pipelines with upward flow. The internal torsion springs hold the plates in the closed position regardless of gravity, ensuring immediate closure upon flow cessation. However, installation in vertical lines with downward flow is strictly not recommended by international valve standards, as gravity would pull the plates open and prevent reliable non-return sealing. When installed horizontally, the hinge pin must always be oriented vertically to allow the dual plates to open symmetrically and equalize wear on both bottom and top hinge points.

In standard Retainer Type dual plate check valves, the hinge pin and stop pin are secured through drilled holes in the outer valve body, which are then sealed using threaded plugs and compression gaskets. In Retainerless Type valves, the internal pins are locked inside precision-machined internal body pockets or an internal carrier sleeve without any through-body penetrations. Retainerless valves are specified by major oil, gas, and chemical companies (e.g., Shell MESC, Saudi Aramco, ExxonMobil) because they eliminate external body leak paths, preventing fugitive VOC emissions and ensuring 100% boundary integrity under extreme pressures up to ASME Class 2500.

Spring selection depends on fluid chemistry, temperature, and cyclic duty. For general water, wastewater, and HVAC applications below 120°C, AISI 304 or 316 stainless steel springs offer reliable performance. For seawater, high chlorides, sour gas ($H_2S$ per NACE MR0175), or high-temperature steam services above 200°C, ZFA recommends Inconel X-750 or Inconel 718. Inconel alloys resist stress corrosion cracking and retain their spring elasticity under extreme temperatures up to 550°C without relaxation or fatigue failure.

Pressure drop is governed by the valve flow coefficient ($Cv$), fluid velocity, and the spring opening cracking pressure. At low flow velocities, the plates may only partially open, causing flow constriction and higher differential pressure. To prevent plate flutter and minimize head loss, pipeline engineers should size dual plate check valves to ensure the regular operating flow velocity exceeds the minimum velocity required to hold the plates fully open (typically $1.5 \text{ to } 2.5 \text{ m/s}$ for liquids). ZFA engineering datasheets provide detailed $Cv$ vs Disc Opening curves for every nominal size from DN40 to DN1800.

ZFA dual plate check valves are tested strictly according to API 598 (Valve Inspection and Testing) and ISO 5208 (Industrial Valves - Pressure Testing). Testing includes: 1) Shell Hydrostatic Test at 1.5x PN/Class rating; 2) High-Pressure Back-Seat Hydrostatic Closure Test at 1.1x rating; 3) Low-Pressure Pneumatic Air Seat Test at 6 bar ($0.6 \text{ MPa}$). For resilient EPDM/NBR/Viton seats, zero visible leakage (Rate A) is enforced. For metal-to-metal seats, allowable leakage strictly adheres to API 598 Table 6 or ISO 5208 Rate D.