is normally open valve and fail open valve the same
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7/31/2019 Is Normally Open Valve and Fail Open Valve the Same
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Is normally open valve and fail open valve the same?
Normally Open" or "Normally Closed" are classifications that refer to actuated (not manually operated)
valves. For an actuated valve, the "normal" state refers to its position when the actuator is not
energized.
Therefore a normally open valve is one that is open until the actuator is energized to close it; if power
to the actuator fails, the valve opens or "fails open".
Likewise with a normally closed valve if power to the actuator fails, the valve closes or "fails closed".
The "normal" state of an actuated valve must not be confused with the "usual" position of the valve
during routine operation of the system. A normally closed valve may be open continuously over a long
period of time while a process is running, but it is still a normally closed valve. It just happens that
this normally closed valve is usually open.
For an actuated valve to return to its "normal" position, there must be some force, often a spring, that
moves the valve from its actuated state back to its normal state. If a valve is actuated to open and
then actuated to close, it will "fail" in whichever position it is in when the activator is de-energized.
This type of a valve is not considered "fail safe".
A normally closed valve might be used in an application such as the loading of gasoline transport
trucks where in the event of a power or automation system failure, you would want to stop flow.
A normally open valve might be used in a situation where you want flow to continue in the event of a
power or automation system failure. This might be the case for the cooling water system for a nuclear
reactor or for an actuated valve on the water piping to the fire protection system.
Control valves, shut-off valves and Fail-safe action valves
Control valves are the valves used to control flow and pressure of the passing medium. The three-way
design are used for mixing or diverting of passing medium.
Shut-off valves are used to shut off pipelines under all normal operating and non-operating conditions. If equipped with electric or pneumatic actuators, its use is in automatic operation. Fail-safe action valves
are control or shut-off valves equipped with actuators with safety function, which ensure closing of the
valve upon power failure.
In the range of LDM valves occupy the mentioned valves largest amount of products. Available in
pressure classes from PN 6 to PN 500, includes a range of nominal sizes DN 15 to DN 400. Execution of
two-way valves can be direct or angle, possibly with an extended outlet socket. Three-way control valves
are generally dimensionally symmetric.
The use of these valves is in the common applications in heating and cooling technology, over-
demanding applications in the field of conventional and nuclear energy to the use of aggressive media in
chemical, pharmaceutical and food industries.