Check Valves permit fluid to flow through them in one direction only.Lift-type check valvesare similarly constructed as globe valves and use a ball or piston, often backed by aspringthat opens under a specified pressure but closes as the pressure decreases, thus preventing backflow. These valves are often suited forhigh-pressureapplications. A variant is thestop check valvewhich doubles as a Globe Valve.

Swing check valvesemploy hinged gates,disc wafers,orwafersthat are often spring-actuated to close against ports as pressure diminishes. These devices can be effective in low-pressure applications. A tilting disc check valve varies the theme somewhat by hinging the gate slightly inward to reduce the pressure required for opening. Butterfly ordouble doorcheck valves use two half-circle gates or wafers that are hinged at the centerline of the valve port and open downstream in the direction of flow.

Rubbercheck valves are also available and include designs such as theflapandduckbillvarieties.Check valvesare used on gas lines, for air service, and with pumps—anywhere that fluid needs to move in a single direction. They can beminiaturized, manufactured inplastic,and may incorporate many special features such asmetal seats.