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Hello

I am preparing datasheet for some "Pressure Regulating Valves", but I don't know how I should determine fail safe position (on fail open or close) of the valves (which are in 2 types Pressure Reducing & Back Pressure Regulator).

Could anyone help me??

Thanks a lot

Hello Saeid,

First of all, I have to say that the term "Fail-safe" is not fully relevant for pressure regulating valves (self-operated). Control valves are devices which are operated by a control signal (electrical or pneumatic) and the actuation signal which is usually pneumatic. In this case, the fail-safe position of the valve means the position (open/close) that the valve will go to in case of control signal or air supply failure.

Whereas, Pressure regulating valves are self-operated devices which are actuated by the line pressure (upstream or downstream). Down-stream pressure regulators open when the pressure downstream reduces below set-point. So when downstream pressure fails, they open fully.

On the other hand, pressure relief valves or back-pressure regulators (upstream pressure control) open to relieve the pressure when the pressure upstream increases above the set point. So when the upstream pressure fails, they remain closed.

In short,

Downstream pressure regulators : Open upon loss of downstream pressure.

Upstream pressure regulators (Back-pressure or relief valves) : Close upon loss of downstream pressure.

Hope this helps. If you have any questions, please contact me.

Ronald Deepak
jronalddeepak [at] gmail.com

Sorry, typo in my post above.

Should read as :

Upstream pressure regulators (Back-pressure or relief valves) : Close upon loss of upstream pressure.

Thanks,

Ronald Deepak
jronalddeepak [at] gmail.com

Dear Ronald,

Thank you very much for your reply, but I had a different supposition about self regulating valves operation. As I know down-stream pressure regulators are passive elements an can only reduce their output pressure (or downstream pressure) with closing more, So when downstream pressure fails, they should close fully. Do think my supposition is False??

Moreover I have some problems with concept of Fail in self regulating valves. For example what does "when downstream pressure fails" mean exactly??

Your kind reply is highly appreciated.
Best Regards
Saeid

Dear Saeid,

The function of a downstream pressure regulator is to maintain the downstream pressure at the desired value (set-point). If the pressure goes below the set point, the regulator opens and sends more flow so that the pressure of the fluid is maintained downstream. When the pressure downstream is close to the set point, the regulator stops sending fluid , i.e., it closes. So when downstream pressure is lost the regulator is opened fully.

Later when I have time, I will explain to you, the operation of a regulator.

Also note that the term "FAIL" is more relevant to control valves to refer to the action of the valve (close/open) when the control signal(4-20mA/HART,etc.) fails or the air supply pressure to the actuator fails. Control valves need external source of power to operate the actuator. So we use these two terms to refer to FAIL position.

A regulator however is a self-operated device and needs no external power to operate. It operates from line pressure. So the term FAIL position is not relevant to regulators.

But for your information, a downstream pressure regulator will open fully when all the downstream pressure is lost, because as I mentioned earlier the regulator will try to send in more fluid and bring the downstream pressure to the set-point.

Hope you are clear now.

Ronald Deepak.
jronalddeepak [at] gmail.com

Dear Ronald,

Thank you very much for your perfect reply. It is very useful for me.

Best Regards,
Saeid