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A blowdown valve (BDV) is a type of shutdown valve designed to depressurize a pressure vessel by directing vapour to a flare, vent or blowdown stack in an emergency. BDVs fail-safe to the open position upon failure of the control system. [1] The type of valve, type of actuation and performance measurement are similar to an ESD valve.
If there is a spring inside of the actuator, it will force the valve open or closed and will keep it in that position while power is restored. An actuator may be specified "fail open" or "fail close" to describe its behavior. In the case of an electric actuator, losing power will keep the valve stationary unless there is a backup power supply.
Shut-off / On-off valve: These valves are either completely open or closed. Examples: Gate valve, ball valve, globe valve, angle valve, pinch valve, diaphragm valve; Check valve: Allows flow only in a single direction; Steam conditioning valve: Regulates the pressure and temperature of inlet media to required parameters at outlet.
A reduced pressure zone device (RPZD, RPZ, or RPZ valve) is a type of backflow prevention device used to protect water supplies from contamination. RPZDs may also be known as reduced pressure principle (RP), reduced pressure principle backflow prevention devices , [ 1 ] [ 2 ] reduced pressure zone assemblies (RPZA), [ 3 ] or reduced pressure ...
Isolation valves, and control valves, that are used for example in systems containing hazardous substances, can be designed to close upon loss of power, for example by spring force. This is known as fail-closed upon loss of power. An elevator has brakes that are held off brake pads by the tension of the elevator cable. If the cable breaks ...
In either case, the motor is usually connected to the water valve via a mechanical coupling. For electrical zone valves, the motor is often a small shaded-pole synchronous motor combined with a rotary switch that can disconnect the motor at either of the two stopping points ("valve open" or "valve closed"). In this way, applying power to the ...
These valves are normally left open so that the user can control the flow of water with the spigot above the sink, and does not need to reach under the counter to start or stop the water flow. However, if the spigot needs to be replaced (i.e. maintenance needs to take place on the system), the isolation valves are shut to stop the flow of water ...
Automatic control valves do not require an external power source, meaning that the fluid pressure is enough to open and close them. Flow control valves, a type of automatic control valve, regulate fluid flow by maintaining a predetermined flow rate, independent of variations in system pressure.