Check Valves
Check valves open and close automatically under the flow of the medium itself: forward flow opens them, reverse flow closes them. They prevent backflow, protect pumps and compressors and suppress water hammer, and are essential on unattended pipeline sections. Closing speed directly affects water-hammer pressure and is a key selection criterion. By design there are swing, lift, dual-plate wafer and ball types. Swing check valves have low resistance and are the most widely used; lift types suit small-bore vertical installation; the dual-plate wafer design is short in length and closes quickly with spring return, reducing water hammer; the ball design is simple, tolerates small amounts of solids and is insensitive to vibration. Pressure ratings cover ASME Class 150–900 (PN 20–PN 150). Body materials include WCB and CF8/CF8M. Sealing is metal-to-metal or soft-seated. Design and manufacture follow API 594, ISO 15761 and ASME B16.34.
Ball Check Valve
The ball check valve uses a spherical ball as the closing member: forward flow pushes the ball off the seat, and on reverse flow the ball returns to the seat to seal. With no hinge or guide parts the design is simple and closing is reliable, making it suitable for media containing a small amount of solids. The ball may be metal or rubber-coated, and soft seating gives good sealing performance. The valve suits water, wastewater, oil and slurry lines, particularly where vibration is present or stable flow is required.
Wafer Dual-Plate Check Valve
The wafer dual-plate check valve uses two semicircular plates that are spring-returned and installed wafer-style between pipeline flanges. Its small size, light weight and short face-to-face length make it the ideal check valve for lines with limited installation space. The two plates close against each other at the centre; the opening stroke is short and response is fast, and a spring can be fitted for rapid closing to reduce water hammer. It suits compact backflow protection in water supply, drainage, circulating water and industrial lines. Design basis: API 594.
Lift Check Valve
In the lift check valve the disc moves vertically along the seat centreline: forward flow lifts the disc, and on reverse flow the disc drops back onto the seat to seal. The design is compact, sealing is reliable and the closing stroke is short, making the valve suitable for small-diameter high-pressure lines. Vertical installation (flow upward) is normally required so that the disc reseats by gravity. Seating may be metal or soft. The valve is widely used at small-bore pump outlets and in steam and gas lines to prevent reverse flow.
Swing Check Valve
The swing check valve uses a disc hinged on the body as the closing member: forward flow pushes the disc open, and on reverse flow the disc falls back onto the seat under the action of the medium and its own weight to seal. The design is simple with low flow resistance, and it is the most widely used type of check valve. Flanged or butt-weld ends are available, with metal-to-metal or soft seating. The valve suits horizontal or vertical installation (flow upward) and is widely used at pump and compressor outlets and on pipelines where reverse flow must be prevented.