Water hammer, (WH) one of the most common problems with check valves, is the generation and effect of high-pressure shock waves that occur in relatively incompressible fluids. These shock waves are produced when a liquid is suddenly forced to stop in a pipe, i.e. closed valve or pump shut down.
Whenever incompressible fluid exists in a piping system, there is the potential for fluid hammer.
DFT Non-Slam Check Valves Effectively Prevent Water Hammer
The risks for water hammer occurring are especially elevated when the fluid’s velocity is high, when there is a large mass of fluid moving, and/or when large elevation changes occur within the piping system.
Within the system, if a swing check valve is used, it relies on either gravity and/or fluid flow in order to close, and therefore the flow reversal must occur before closure begins.
When the swing check does finally close, it abruptly stops the flow, causing a pressure surge that results in shock waves, which continue until the energy generated from this closure dissipates.
These pressure surges and waves exert extremely high forces and act against the piping and the valve, causing very high stress on the metal, along with vibrations in the system.
Preventing Further Damage
When a system is not designed to withstand these high transient forces, the results can be ruptured pipes and/or components, and further damage. In fact, water hammer commonly causes noise, vibration, and hammering pipe sounds, which may eventually result in equipment damage, flange breakage, ruptured piping, and damage to pipe supports.
These problems can be greatly minimized or even eliminated by installing a spring assisted, non-slam check valve. Because non-slam check valves do not rely on gravity or fluid flow for their closure fluid hammer isn’t a problem.
With a non-slam check valve, the disc is closed by the spring assist on the valve as the forward velocity of the fluid slows. The spring assist, along with the relatively short distance the disc must travel, mean that by the time the forward velocity had decreased to zero, the valve disc has reached the seat and the valve is already closed.
Reverse flow is eliminated, and therefore the forces necessary to produce WH on the upstream and downstream sides of the valve are substantially eliminated as a result.