What is a clay stopcock? ...

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Answers:    A clay valve is a type of spout designed to do different things. The most common is surrounded by water a supply system. When pumping hose down the valve will not amenable until the pressure behind it reach a pre-determined amount of pressure. They then set them up on how hastily they want them to open. When the flow/pressure drops the tap will slowly close. The speeds for both opening and closing are usually adjustable..
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A spigot manufactured by the CLA-VAL company. These are valves that are controllable, or self-regulating. For instance they can be arranged to assert a constant outlet pressure. They are used in industry and surrounded by fire protection systems. In one application they are mounted on piping systems that are pressurized with nouns. If air pressure is lost, the valve can open automatically to grant water.