Check valves can be found in nearly every application where a pump is required. Check valves allow for flow in one direction while preventing back flow when fluid in the line reverses direction. Because check valves are self-automated they require only line pressure to open and close, making them a worry-free installation in most cases.
A problem that can occur when using the incorrect check valve in an application is water hammer. Water hammer is a surge of pressure caused when a fluid in motion is forced to stop or change direction suddenly (often occurring at an elbow joint). There are many recorded cases of water hammer so severe they have ruptured pump casings, expanded and ruptured piping and even vibrated buildings right down to their foundations. Taking the time to find the correct style of check valve for the situation, and installing that valve properly will avoid any danger of water hammer taking place.
This is what the wrong application can do to a valve in as little as six months.
Silent check valves were developed to eliminate water hammer problems connected with the use of conventional swing check valves. The disc in a traditional swing check valve swings onto the seat to block reverse flow, or swings off the seat to allow forward flow. The most common type of installation includes the use of a pump and a swing check valve installed in the pump discharge piping. In theory, the swing check valve closes quickly when the pump shuts down - it does, but not quickly enough. Reversal of flow in the piping will slam the disc closed against its seat and cause noise, vibration and piping stresses, which can be easily controlled by the use of a spring loaded silent check valve.
In short, swing check valves depend upon reversal of flow to close. Silent, spring loaded check valves are designed so that the disc returns to its seat at zero velocity before the reversal of flow occurs. The most common application for silent check valves is in pump discharge piping.
Silent check valves should never be installed directly on a pump discharge line or near elbows. This will result in longer life of the valve as the components are not directly exposed to turbulent flow. It is most desirable to locate the valve as far as possible from the pump discharge or elbow, 5 - 10 pipe diameters is a minimum recommendation.