Check Valves and Pumps

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Check Valve and Pump Descriptions

This page describes briefly the principles of check valves and pumps. A check valve is a one-way valve for fluid flow. There are many ways to achieve one-way flow, and a couple methods are illustrated here.

Check Valves

Device A consists of a ball bearing retained by a spring. Fluid flowing to the right will push the ball bearing against the spring, and open the valve to permit flow. This device requires some pressure to compress the spring and open the valve. If an attempt is made to flow fluid to the left, the ball bearing seals against the opening, and no flow is allowed. This is a modern design that requires round balls.

Device B is simply a flapper (colored yellow) that is anchored on one side. The flapper can be a hinged metallic door, a thin piece of metal, or a piece of rubber or polymer. This is the simplest design, and was used on early pumps.

Pumps

Two methods of incorporating check valves into pumps are shown to the right. In schematic A, the check valves permit expulsion of the fluid to the right on the downward stroke while denying flow to the left. On the upward stroke, the pump fills from the left, while denying reverse flow from the right.

The design in schematic B is somewhat different. The piston has one or more holes drilled though with a check valve on each hole. (One hole is illustrated). On the downward stroke, the fluid moves from below the piston to the chamber above the piston and is denied from exiting to the left. On the upward stroke, fluid is pushed out the exit on the right and simultaneously more fluid is drawn from the entrance on the left. Case B is the design illustrated by Watt in his patent and described as the air-pump since it would pump air as well as water.