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A petcock is a small shut-off valve used to control the flow of liquid or gas.Historically, petcocks were threaded valves controlled by a butterfly handle; [citation needed] modern petcocks are typically ball valves.
The simplest and most common general type of plug valve is a 2-port valve [1] [2] with two positions: open to allow flow, and shut (closed) to stop flow. Ports are openings in the valve body through which fluid can enter or leave. The plug in this kind of valve has one passageway going through it.
The sheet has a solid end and a flow-through end; sliding it from one position to the other opens or stops the flow. Also called sliding blind valve; Outflow valve: regulates flow and pressure, part of cabin pressurization; Pilot valve: regulates flow or pressure to other valves; Petcock, a small shut-off valve
Backflow preventers are categorized into three groupings: Assembly, Device or Method. With the exception of elimination, these are the only ways one can control backflow from taking place. The eight named backflow assemblies all have two resilient seated isolation/shut off valves with properly located test ports.
Turning a valve knob or lever adjusts flow by varying the aperture of the control device in the valve assembly. The result when opened in any degree is a choked flow . Its rate is independent of the viscosity or temperature of the fluid or gas in the pipe, and depends only weakly on the supply pressure , so that flow rate is stable at a given ...
Vent and drain valves are examples of normally closed valves which are only opened when required to depressurise (vent) or drain fluids from a system. Isolation valves must effectively stop the passage of fluids. [4] Gate valves, ball valves and plug valves are generally considered to provide tight and effective shut-off. Globe valves and ...
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The shut off butterfly valve for a Francis turbine at Gordon Power Station, Tasmania Ball valve The "seat" is the interior surface of the body which contacts the disc to form a leak-tight seal. In discs that move linearly or swing on a hinge or trunnion, the disc comes into contact with the seat only when the valve is shut.