Editing Check valve (section)

===Swing check valve===
[[File:Swing Check Valve Opening and Closing.webm|thumb|right|Swing check valve opening and closing]]
A swing check valve (or tilting disc check valve) is a check valve in which the disc, the movable part to block the flow, swings on a [[hinge]] or [[trunnion]], either onto the seat to block reverse flow or off the seat to allow forward flow.  The seat opening cross-section may be perpendicular to the centerline between the two ports or at an angle.  Although swing check valves can come in various sizes, large check valves are often swing check valves. A common issue caused by swing check valves is known as [[water hammer]]. This can occur when the swing check closes and the flow abruptly stops, causing a surge of pressure resulting in high velocity shock waves that act against the piping and valves, placing large stress on the metals and vibrations in the system. Undetected, water hammer can rupture pumps, valves, and pipes within the system.<ref>{{Cite news|url=http://www.dft-valves.com/check-valves/|title=Check Valves|work=DFT Valves|access-date=2017-10-26|language=en-US}}</ref>

The [[flapper valve]] in a [[Flush toilet#Tank style with flapper-flush-valve|flush-toilet mechanism]] is an example of this type of valve. Tank pressure holding it closed is overcome by manual lift of the flapper. It then remains open until the tank drains and the flapper falls due to gravity. Another variation of this mechanism is the '''clapper valve''', used in applications such [[firefighting]] and fire life safety systems. A hinged gate only remains open in the inflowing direction. The clapper valve often also has a spring that keeps the gate shut when there is no forward pressure. Another example is the [[backwater valve]] (for sanitary drainage system) that protects against flooding caused by return flow of sewage waters. Such risk occurs most often in sanitary drainage systems connected to combined sewerage systems and in rainwater drainage systems. It may be caused by intense rainfall, thaw or flood.