Shut off pressure 1

[bif]

can someone give me a definition of 'shut off pressure' on an automated isolation valve. The valve is spring return fail close butterfly valve.

Is the shut off pressure the maximum process line pressure where the valve is gauranteed to close and not to pass, or something else?

 

[pleckner]

The shut off pressure is indeed the maximum pressure upstream of the valve and the coincident minimum pressure downstream of the valve. The type and cost of the actuator will depend on this number as well as the allowable leakage.

 

[JLSeagull]

Consider using the "design pressure" or maximum flange class pressure upstream and zero downstream, then include a 1.4 torque safety factor and base the spring on a minimum air pressure. For example if the air system is normally 100 psig, size the spring for 70 psig and set a pressure regulator on the actuator for 70 psig. This conservative basis causes one to buy a larger, heavier actuator than some require.

Obtain valve torques to begin opening, begin closing and traveling. Verify the actuator torque against the valve torque in all situations. Assure that the testing is witnessed and results such as opening and closing times are recorded. The valve will perform better in a shop with no pressure applied than it will when installed. If you don't like the way it works in the shop -- you really won't like the way it works a year after it is installed.

 

[Ashereng]

In the oil and gas industry, the maximum shutoff pressure is taken as the maximum ANSI class pressure. So, on a 300# system, the shutoff pressure (actually, it is a differential since we also assume atmospheric on the other side) is 740 psi.

This is process shutoff pressure. It has nothing to do with sizing the actuator.


For the actuator, we size the actuator on 80 psig minimum (if you use less, say 70 psig, then you will need a larger actuator). On most I/A system, you will have around 100 psig for your valve.

Add to it the valve friction and then add 40% safety margin, you now have the torque requiremnt to actuate the valve.

This is also the spring's (on the spring return) torque requirement.

Should there then be a closing time requirement, then you may need to go even larger.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[BigInch]

If there is a pump around, its the pump's discharge pressure when the valve is closed.

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