Check valves are installed in many piping systems. Their purpose is to allow flow in only one direction, which can be critical for plant safety and to protect equipment from damage.
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There are a few different check valve designs, including swing check valves and spring-loaded poppet-style check valves. Understanding which type is best for a given application and ensuring valves are properly installed is vital to success.
Noah Miller, applications/engineered sales manager with Check-All Valve Manufacturing Co., and Brian Strait, business development and marketing manager with Check-All Valve, explained the differences between check valve designs, and offered installation and sizing tips as guests on The POWER Podcast. Check-All Valve is a West Des Moines, Iowa-based manufacturer of industrial spring-loaded poppet-style check valves.
Miller explained that piston poppet check valves have two main advantages over swing check valves. The first concerns water hammer, which is hydraulic shock, caused when water stops or changes direction suddenly. &#;Once that wave gets to the swing check, it&#;ll push that clapper closed and actually slam it shut, which will promote that water hammering effect,&#; Miller said. However, the spring inside a piston poppet-style check valve helps minimize, and may even eliminate, water hammer, because it closes the valve before the pressure wave arrives.
&#;The secondary aspect or advantage of the piston poppet over a swing check is installation orientation,&#; Miller said. &#;A swing check is only supposed to be installed in a horizontal-flow position. Whereas, a spring-loaded piston check can be vertical-flow up, vertical-flow down, 45 degrees, 37 degrees, you can kind of pick and choose with that spring, because it allows it to still close in a static condition in the piping system.&#;
Another consideration when installing check valves concerns the run of piping. Miller noted, &#;Ideally, you&#;d like to have a minimum of 10 pipe diameters of straight pipe on the upstream side of the check valve.&#; The reason is to ensure the flow through the valve is laminar in nature, that is, fluid particles flowing in smooth layers, with little or no mixing. Miller said that will maximize the effective valve life.
Getting a valve sized correctly for the application is also important. The goal is for a check valve to always be either fully open or fully closed. &#;Pressure and flow together create pressure drop across the given check valve,&#; Miller said. &#;You can have enough of one, but not enough of the other.&#;
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Miller presented an example of a system with 300 psi of pressure, but only 0.005 gpm of flow. He said, &#;You&#;re not fully opening any check valve, it doesn&#;t matter what style it is, because you&#;ve got enough pressure, but you don&#;t have enough flow, and that pressure and flow together create that pressure drop to fully open the valve.&#;
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&#;Aaron Larson is POWER&#;s executive editor (@AaronL_Power, @POWERmagazine).
Flapper checks are not good. You want a metal, spring loaded, poppet style check valve. However, any check valve will fail when it is slamming closed every time the pump cycles off. Adding a Cycle Stop Valve to your pump will not only stop the check valve from slamming, but will give you strong constant pressure in the shower instead of cycling the pump on/off repeatedly, which also makes the pressure go up and down repeatedly. The CSV will not only make check valves last longer, but also the tank bladder, the pressure switch, and most especially the pump/motor.
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