Piston & Ball Check Valves
Piston and ball check valves, like all check valves, are used to prevent back flow
in the line. Standard valve design has no spring in order to minimize cracking
pressure and pressure drop, it will only function properly when installed in a
horizontal line. As an option the designs can include a spring to assist closing and
for use in 90-degree styles installed in vertical lines.
PISTON CHECK VALVE
The pressure of the fluid passing through a system opens the valve, while any
reversal of flow will close the valve. In Piston, or lift, check valves a body-guided
disc moves within the body bore. The body guide ensures alignment of the seat
and disc when the valve closes. The valve is installed with the flow under the
disc, so that the inlet line pressure and flow rate will force the disc to “lift” off the
seat and allow the line fluid to flow through the valve. Should the flow suddenly
reverse itself, the disc will automatically and quickly, assisted by the weight of the
disc, be forced to the closed position, preventing the line fluid from returning.
Exercise caution when these valves are used for dirty media because that media
could cause the disc to stick inside the body bore.
BALL CHECK VALVE
The function of ball check valves is similar to the piston check, but the ball check
valves use a “ball” inside the body to control the movement of flow.
The ball is free to rotate, resulting in even wear and a wiping action between the
ball and seat. This feature makes ball checks useful for viscous media.