swing check valves and horizontal and vertical lift check valve, and the ball check valve
There are three basic designs of the Check Valves: the swing check valve, the horizontal and vertical lift check valve, and the ball check valve.
swingCheck Valves are the most popular of all check valves since they offer very little resistance to the flow when in wide open position. They are generally used on all piping where the pressure drop is of prime importance. Swing check valves are used for handling liquids, and can be installed in vertical or horizontal position without impairing their performance. However, these check valves are not recommended for such applications where the reversal of flow is frequent, since this causes the valve disk to fluctuate rapidly and result in "valve chatter.
Horizontal Check Valves are quite frequently assembled on the same valve bodies as those used for the regular globe valves. They are generally used for such applications where the reversal of flow and pressure fluctuations are very frequent, since they have less tendency to develop "disk slam" and valve chatter. Horizontal lift check valves are used for handling steam, air, and gases on horizontal piping lines, and they are not recommended for installation on vertical piping systems.
Vertical lift check valves are similar in construction to horizontal lift check valves, and are especially designed for installation on vertical piping systems. Another modification of the vertical lift check valve is the angle vertical check valve, which is used on right angle turns in the piping systems.
Ball Check Valves are designed to handle viscous fluids, and for services where scale and sediment are present. These valves, usually made in vertical, horizontal and angle designs, are particularly recommended for rapidly fluctuating lines because of their quiet operation. During the ball check valve operation, the ball rotates constantly, equalizing the wear on the ball and seat; thus prolonging the life of the valve.
Some of the swing check valves have external lever and counterweight balance arrangement, to make the valve disk more sensitive to the flow and open under a minimum of fluid pressure. Further design variations of the check valve include the stop Check Valves and non-return valves.
Stop Check Valves sometimes called "screw-down" check valves, are actually modifications of the globe or angle valves. This modification consists of making a slip stem connection to the valve disk instead of using the disk locknut. In this design, the disk can be closed by hand, but can be opened only by the check valve action; i.e., by the fluid pressure under the disc. Probably the most common application of the stop check valve is in safety non-return valves. The ASME Boiler Code specifies these valves for the boiler nozzle of every boiler, when two or more boilers are connected to the same header. These valves are also called boiler stop check valves, or boiler "screw-down" checks.
