Cutoff valve and reflux valve

Cutoff valve

A cutoff valve (sluice or gate valve) is used to fully stop or fully allow the flow; it is not used for throttling.

      wheel / spindle
          |
       __ | __
      |  [|]  |   <- gate (wedge) moves up and down
  ====|  | |  |====
      |__|_|__|
         body

• Construction: a cast-iron body with a wedge-shaped gate (disc) that is moved across the flow by a screw spindle turned with a hand wheel.
• Working: when the wheel is turned, the gate either rises (valve open: full bore, little head loss) or comes down across the pipe (valve closed: tight shut-off).
• Uses: at the start of branches, at intervals along the main lines (sectional valves), and before and after pumps and meters.

Reflux valve

A reflux valve (also called a non-return or check valve) allows water to flow in one direction only and closes automatically when the flow tries to reverse.

   flow ->   _______hinge
   =========|\       |=========
            | \ flap |   (flap lifts for
   =========|__\_____|=========  forward flow,
        valve seat           falls shut on reversal)

• Construction: a cast-iron body with a flap (door or disc) hinged at the top, which rests on a seat. Forward flow pushes the flap open; when the flow stops or reverses, the weight of the flap and the back pressure press it onto the seat.
• Uses: on the delivery side of a pump, to prevent back flow when the pump stops and to protect the pump from water hammer; on pipes from a reservoir that must not drain back; at the foot of a suction pipe (foot valve); and on rising mains and service connections to prevent back siphonage.