Check valves consist of several moving parts; therefore, minimizing friction between these components through lubrication can extend the life of the valve components, enhance overall performance, and ensure efficient operation.Finally, valves must be installed correctly and used as directed. Improper valve installation, or using the wrong type of check valve, can reduce the lifespan of the valve. A regular maintenance schedule should also be implemented to ensure that faulty valves are replaced at the first sign of failure.When selecting a valve size, remember to assess the check valve based on the given application, not the size of the pipeline.Oversizing pipes is a common practice that takes into account future capacity requirements. However, large pipe diameters produce lower flow rates, which means that there may not be enough fluid velocity to fully open the check valve. This can cause swing valves, which are sized for the pipe diameter, to flutter back and forth between the partially open and closed positions. This phenomenon is known as chattering. The frequency of movement due to chattering can eventually increase the rate of valve wear and cause components to fail, leading to further damage to other downstream equipment.
Therefore, check valves must be selected based on the expected flow. This involves choosing a valve with the appropriate valve coefficient value. The value describes the ability of the flow media to open the valve fully; the higher the CV, the greater the flow rates required to open the valve.Consideration must also be given to the type of media that will be passing through the valve. For instance, corrosive or abrasive media may require the use of certain valve materials, such as carbon steel, stainless steel, or brass. Also, the properties of the fluid passing through the pipeline need to be considered to ensure that flow can occur uninterrupted. Solids, liquids, and gases all differ in viscosity, density, mass, and so on. The internal valve mechanism must allow these unique media to be accommodated.Valve orientation is also essential for determining the right type of check valve for a given application. Some valves may not work as intended when installed for vertical flow situations. Furthermore, if the valve is deemed suitable for vertical flow, the direction up or down must be determined, as these conditions come with unique requirements.Although all check valves perform the same function, they differ in the way their internal mechanisms permit one-way flow.
Each of these mechanisms lends itself to different situations; therefore, it is essential to understand the underlying mode of operation of these valves in order to determine their most suitable applications.Ball check valves consist of a ball that is pressed by a spring onto a seat in the closed position. When flow is induced on the upstream side, the ball moves and the spring is compressed. When the flow is shut off, the ball is moved back into the seat to prevent reverse flow.Dual plate check valves consist of two plates joined by a torsional spring in the middle. Fluid opens the check valves and builds up torsional stress in the spring. When the flow is stopped or reduced, the spring releases the energy to snap the valve shut.Spring-assisted check valves are relatively new compared to other internal valve mechanisms. With this valve type, flow opens the valve by opposing the motion of an internal spring.
When there is constant and sufficient flow, the valve remains fully opened, and the spring is held in compression. When the flow is removed, the spring releases the built-up potential energy to quickly snap the valve to the closed position. The valve is closed before the flow reverses, which reduces the possibility of water hammer.In this type of check valve, fluid flow from upstream lifts a piston upward to open the valve and permit flow downstream. Once the pressure is removed, gravity pushes the piston back to its original closed position to prevent reverse flow.Swing check valves are the oldest and most common type of valves. Fluid flow swings open a disc that rotates on a hinge to open the valve. When flow is reduced, gravity and reverse flow move the valve back to the closed position.