A check valve, clack valve, non-return valve or one-way valve is a valve that normally allows fluid (liquid or gas) 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 are often part of common household items. Although they are available in a wide

range of sizes and costs, check valves generally are very small, simple, or inexpensive. 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. The bodies (external shells) of most check valves are made of plastic or metal.

An important concept in check valves is the cracking pressure which is the minimum upstream pressure at which the valve will operate. Typically the check valve is designed for and can therefore be specified for a specific cracking pressure.

There are different kinds of Check valves, each adapted for different pressures and different usage.

1.Forged Check valve Generally, forged type would be used when the size of gate valve is smaller than 2"(DN50).Forged steel is the main material.Flanged, Socket Welded, Thread and Butt Welded connections are available.

2.Disc Type Check Valve Disc Check valve is type of swing construction. It has single or double plate.

The body is made by casting iron or casting steel. Both of soft seat and metal seat is available.

3.Swing type Check Valve The body of this kind Swing Check valve is not like the disc check type. They have the body likes globe valve.

4. Lift check valve Lift check valve is loaded by spring. The piston is lifted when the fluid comes through.