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Thanks for all your replies. I was just curious because I had seen some some old specs that have: 1) Flow to close - Failed closed 2) Flow to open - Failed Closed. I've also noticed from the old spec that item 1) was used with angle valves where the pressure drop is large (2500 psig) for a...

Thank you all for the inputs. They all are very helpful. So, it appears that selecting a the flow-to-open or flow-to-close valve has an effect in selecting the type of actuator also? If so, when do I specify a "piston" type actuator or "diaphragm" type actuator? Is there a general rule of...

MortenA, Could you tell me more about your exception with Fire Case? Thanks

Thanks all for your responses. If the valve is fail closed (or if there is no air supply, the valve is closed), is there a mechanical or stability advantage to select the valve stem/plug to close when there is flow. In other words, is there an added advantage to have a valve flow to close or...

Does anyone have a general rule to specify control valves either "flow to open" or "flow to close"? I have seen control valve specs requiring both "flow to close" and fail "closed" or "flow to open" and fail "closed". Is there a major advantage to specify one or the other? Thanks for all your...

Is there a general rule to determine what is the relief temperature for blocked outlet, thermal expansion, loss of liquid seal, thermal expansion at suction of pump, pump discharge blocked in, etc.? Is it safe to use Relief temperature = (oper. temp./op. press.) x relief pressure for these...

I have an upstream vessel (A) that has a letdown valve at the bottom outlet which connects to another downstream vessel (B). I have to size a PSV for the downstream vessel (B) for loss of liquid seal from the upstream vessel (A). How do I determine the required flow capacity for the PSV...

Thanks, Latexman.

Can you select a balance bellow type valve and forget about the backpressure in your calculation?

Latexman, Thanks. I started another thread per your suggestion. MortenA, Thanks, but usually for the basic design package, the simulated process package is done for normal unit operation and the relieving conditions are not part of it.

I am trying to size some PSV's that have properties (hydrocarbons) with MW < 40 and Relief Pressure above 2000 psig. The API curve has a minimum of MW = 40 and a max pressure at 1000 psig. For Fire case, how do I obtain the Latent Heat of Vaporization and Relief Temperature at the conditions...

I am trying to size some PSV's that have properties (hydrocarbons) with MW < 40 and Relief Pressure above 2000 psig. The API curve has a minimum of MW = 40 and a max pressure at 1000 psig. For Fire case, how do I obtain the Latent Heat of Vaporization and Relief Temperature at the conditions...