All quick disconnect couplings consist of a socket and a plug. The design of the coupler varies due to placement of the shut-off valve. This variation allows you a choice of three types of couplers: a one way shut-off, a two way shut-off and a straight-thru.
Incorporate a valve in the socket portion which is connected to the upstream pressure side of the coupling. The plug portion has no valve. When you disconnect the coupling the valve shuts off the flow instantaneously on the pressure side.
Incorporate valves in both parts of the coupling, socket and plug. This design is important in hydraulic applications, and where loss of the media being transmitted could cause serious problems when couplings are disconnected.
Do not have valves in either portion of the coupling. They provide the least resistance for maximum flow, but caution must be exercised in their use. Pressure on lines must be relieved before they are disconnected.