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Under normal flow I would agree that this force would be negligible, but imagine a flow at the maximum possible velocity in a pipe. It seems intuitive that the required shearing force increases and could be significant for at least part of the travel. I actually do have an application and...

I am not trying to size an actuator - I have that info. I need the force required to shear a fast moving stream.

I am interested in a force that might not normally be considered in actuator sizing for Gave Valves. Normally considered forces are stem friction, seat friction, and hydrostatic. However, it seems there is another force that could be significant under some circumstances, e.g. a higher...

It recently came to my attention that several operating companies are opening parallel, 100% sized, relief valves to the process when the design was to leave one closed and one open to facilitate maintenance. This is apparently becoming a standard practice. Normal sizing practice involves...

I am currently working on a simulation to demonstrate the issues associated with this practice.

Compositepro, Thank you for your comments. My concern is not with sizing deficiencies at all. My concern is with taking two, individually proper sized valves and opening them to the process when the design calls for only valve being open to the process. Opening to the process refers to the...

MortenA You are absolutely correct. There is no problem with interlocking the valves. This thread has to do with opening both valves to the process at the same time when only one was intended by design. Please see my paper at http://www.scribd.com/doc/18656992/Relief-Valves-in-Parallel Your...

I have placed a paper on this subject up on Scribd. http://www.scribd.com/doc/18656992/Relief-Valves-in-Parallel

When there is no basis for sizing, it becomes difficult to justify selection. Some vendors don't want to supply a valve without a basis and without a calculation. I have seen process engineers make up an imaginary liquid for fire sizing when no other case exists and still use the properties...

A relief valve is, at its basis, a on-off orifice. If you are looking for a simple calc, I have worked up an orifice calc spreadsheet for gas that allows you to substitute a relief valve orfice designation. It should not be used for final relief valve sizing of course but it does have its...

It recently came to my attention that several operating companies are opening parallel, 100% sized, relief valves to the process when the design was to leave one closed and one open to facillitate maintenance. This is apparently becoming a standard practice. If more than one relief device is...