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The valves are normally installed with the first installation of a system, then remain in place for the life of the system. They are generally reliable and require no maintenance. If they do eventually fail, they are replaced rather than repaired. A leaking valve commonly shows a dribble of water from the air vent, or stains of rust or limescale.
A sewer pipe is normally at neutral air pressure compared to the surrounding atmosphere.When a column of waste water flows through a pipe, it compresses air ahead of it in the system, creating a positive pressure that must be released so it does not push back on the waste stream and downstream traps, slow drainage, and induce potential clogs.
Each fixture usually has a characteristic means of connection. Normal plumbing practice is to install a valve on each water supply line before the fixture, and this is most commonly termed a stop or "service valve". The water supply to some fixtures is cold water only (such as water closets and urinals). Most fixtures also have a hot water supply.
Old water pipe, remnant of the Machine de Marly near Versailles, France. Lead was the favoured material for water pipes for many centuries because its malleability made it practical to work into the desired shape. Such use was so common that the word "plumbing" derives from plumbum, the Latin word for lead.
A trap primer (or trap seal primer) is a plumbing device or valve that adds water to traps.The water seals in traps are needed to prevent sewer gases from entering buildings, but because this water is exposed to the air, it is subject to evaporation over time in infrequently used floor drains, leading to the release of sewer gas into the environment.
There is no feedback to verify the state of the valve, which is assumed to do what has been commanded. Zone valves can also be constructed using wax motors and a spring-return mechanism. In this case, the valve is normally closed by the force of the spring but can be opened by the force of the wax motor. Removal of electrical power re-closes ...
Larner–Johnson Valve: needle control valve often in large sizes used in water supply systems; Leaf valve: one-way valve consisting of a diagonal obstruction with an opening covered by a hinged flap; Line blind valve: a thin sheet oriented perpendicular to the pipe. The sheet has a solid end and a flow-through end; sliding it from one position ...
Pneumatically-actuated globe valves and diaphragm valves are widely used for control purposes in many industries, although quarter-turn types such as (modified) ball and butterfly valves are also used. Control valves can also work with hydraulic actuators (also known as hydraulic pilots). These types of valves are also known as automatic ...