Piston Check Valves
The fluid pressure that passes through a device opens the valve whereas the valve is closed by any inversion of flow. Piston, or lift check valves use a body-guided disk which moves inside the body up and down.
The body guides guarantee the proper alignment of the seat and disk configuration when the valve is closed. The valve is mounted with the flow below the disk, so the pressure and flow rate of the inlet line will force the disk to "float" off the seat, allowing the line liquid to stream through the valve.
If the flow unexpectedly reverses itself, the disk will be forced to the closed position automatically and rapidly, helped by the weight of the disk, stopping the return of row fluid.
When using these valves for dirty media, proceed with caution because that media could cause the disk to settle inside the body cavity.