Questions regarding solenoid valves NO and NC
Thread Content
NO and NC are often confused. For example, when a solenoid valve fails and is in the off state, it should be connected to NC, while when it is in the on state it should be connected to NO. Is this understanding correct?
NC: Normal Close, which means it is turned off when not powered on； NO: Normal Open, which means it is open when no power is applied. It refers to the normal on/off state, not a description of the fault condition.
Isn’t it off at cut-off and on at cut-off?
The question refers to the normally open and normally closed contacts of solenoid valves, not the fault-open and fault-tube states associated with pneumatic valves.
Is the feedback wiring for the valve switch unrelated to the fault condition?
What signals does the DCS receive? Open point, closed point?
The question is: Solenoid valve? Pneumatic control valve driven by a solenoid valve? The valve position switch on the pneumatic control valve? The questions are confusing.
Refer to ASCO’s solenoid valve selection guide: for NC solenoid valves, when the coil loses power, the air inside the valve actuator is released through the solenoid valve.