Solenoid Valves Question

Hello All,

Just a rookie question regarding Solenoid Valves. This is my first PLC program and I have several solenoid Valves that need to be opened and closed. Would a 1 be an open signal and a 0 be a close signal? Or does it depend on the valve whether it is Fail Open or Fail Closed?

Please let me know.

Thanks

Yes, you can specify if you want a Normally Open (fail open) or Normally Closed (fail closed) valve depending on application.

Brian.

elmatador said:

Or does it depend on the valve whether it is Fail Open or Fail Closed?

Click to expand...

Yes it depends... you can buy the valve normally open or normally closed, both conditions are when voltage is not applied to the coil, this is the normal state

Edit: beat by less the 60sec...

You can also buy two-coil solenoid valves that require power to shift from one position to the other and will maintain that position when power is removed.

The point is that there is a wide enough variety of solenoid valves that you should beware of generalizations. Before writing the PLC program it is your responsibility to find out what type of solenoid valve your program will be controlling. A program that is correct for one type of solenoid valve could be dangerously wrong for a different style solenoid valve.

also be aware that some solenoid valves can be tubed up to be either/or. so just because one solenoid on the panel is normally closed doesnt mean the next one is also.

Here's a site that you can check out:

http://www.hydraulicspneumatics.com/200/eBooks/Article/True/45152/

The biggest difference is air or hydraulics. My applications are with air. Failsafe is a no-air condition. The safety criteria is 'no stored energy' after an EMO. For me, almost all valves are normally closed pilots that drive another air-driven device. Than means when I do programming, a 1 or on is open, 0 or off is closed. Exceptions are rare.
I note exceptions in the text of the associated rung so there is no confusion.

elmatador said:

Hello All,

Just a rookie question regarding Solenoid Valves. This is my first PLC program and I have several solenoid Valves that need to be opened and closed. Would a 1 be an open signal and a 0 be a close signal? Or does it depend on the valve whether it is Fail Open or Fail Closed?

Please let me know.

Thanks

Click to expand...

Depends on the type valves being used. The majority of process valves are operated with air to open and spring to close. The solenoid valve supplies air to the head of the process valve, where the air pressure pushes against a baffle that is being held in place by a spring. When the total surgace area air pressure is greater than the force exterted by the spring, the actuator inside the valve opens or closes the valve depending on the type of process valve. These types of valves are failsafe, whenever the air is removed, the valve returns to its state determined by the spring.

Piston valves usually are operated by air to open and air to close. When the air supply is removed, these valves remain in the last position unless some force is exterted on the piston, in which case the piston will move in the direction of the force.
Usually these types of valves can be operated with a 5 way solenoid. These air solenoids have two air ports, a normally opened and normally closed . Air is always on the normally closed port until the solenoid is activated, then air switches to the normally open port.

Thank you guys for the insight on the various types of valves out there.

On the P&ID's I have, there are three MOV's that are FC and one is FL. Then i have four solenoid valves that are FC.

Also, any idea what FL means? Is it "Fail-last".

Please correct me if I am wrong, my understanding is as follows for the outputs from a PLC to a valve:

Fail Open Solenoid Valve:
1: Close
0: Open

Fail Close Solenoid Valve:
1: Open
0: Close

Fail last??

FL - Stay where you are

I Googled 'fc fl valve' and found this page.

FO - Fail Open
FC - Fail Closed
FL - Fail in the Last position. If open, stay open. If closed, stay closed.
That valve would have 2 coils. One to open, the other to close.

elmatador said:

Fail Open Solenoid Valve:
1: Close
0: Open

Click to expand...

This would be true for a 2 Position Normally Open Valve with a spring return.
If the output does not come on, the valve remains open.

elmatador said:

Fail Close Solenoid Valve:
1: Open
0: Close

Click to expand...

This would be true for a 2 Position Normally Closed Valve with a spring return.
If the output does not come on, the valve remains closed.

elmatador said:

Fail Last?

Click to expand...

By fail last, it probably means that if the output Fails it stays in what ever position the valve was last in. This would be a 2 Position Detented Valve, with two coils. For this type of valve you need two seperate outputs. Turning on one output shifts the solenoid one direction. Turning on the other output shifts the solenoid in the opposite direction.

If the outputs do not come on, the vavle will remain in which every position it was last in.


This is a very small sampling of all the possible valve combinations. The PLC control portion of the PLC is only part of what determines how the valve behaves, the other part is how the valve is configured physically.