A check valve allows fluid to flow through it in only one direction. Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave. There are various types of check valves used in a wide variety of applications. Check valves work automatically and most are not controlled by a person or any external control; accordingly, most do not have any valve handle or stem.
For carbon steel check valves, the seat material is usually forged steel. The sealing surface of the seats is spray welded with hard alloy specified by the customer. Renewable threaded seats are used for NPS≤10 check valves, and welded-on seats are optional. Welded-on seats are used for NPS≥12 carbon steel gate valves. For stainless steel check valves, an integral seat is usually utilized, i.e. by welding hard alloy directly within body cavity. Threaded-in or welded-on seats are also optional for stainless steel check valves, if required.
Stainless steel + flexible graphite wounded gaskets are used for Class 150 and Class 300 check valves; stainless steel flexible graphite wounded gaskets are used for Class 600 check valves, a ring type joint gasket is used for Class 900 check valves; a pressure seal design is used for Class 1500 and Class 2500 check valves
The body and bonnet of Class150 to Class 900 check valves are usually connected by with studs and nuts. And the body and bonnet of Class 1500 to Class 2500 check valves usually utilize a pressure seal design.