Ditto the above replies, but additionally:
1) If you have a multi-section machine, be aware that stonewall in one section may drive one or more of the other sections into surge, which is potentially more damaging. If, for example, you have a 2-section compressor with a fixed outlet pressure...
Is there a good way to show PLC control logic, both analog and discrete, on a PFD? How would one show manually-inputted PLC parameters (e.g., a manually-inputted flow limit)?
The rule of thumb I've used in the past with good success is: One pipe diameter of suction straight-run for every fps of suction line velocity. Usually this is about 5 diameters, but in some cases, velocities may necessarily be higher or lower.
I asked AspenTech why they use inlet SG to calculate discharge pressure in Hysys. Here's what they said:
"The ideal head, h, can easily be defined as a function of the isentropic or polytropic work. The relationship is:
(1) W = MW*F*g*h
where:
W = ideal pump power
MW = molecular weight of...
The fluid is a light hydrocarbon mixture, with a pump delta-T of about 50F degrees. Though the SG decrease is small in percentage terms, the pump TDH is on the order of 2000 ft. Therefore the absolute pressure difference is significant for our application.
Thanks for the input everyone. Interestingly, the process simulator that I typically work with (Aspen Hysys) uses inlet SG to convert pump TDH into pressure. It might be instructive to simulate this in Pro2 or Aspen+ to see if they agree.
In the past, I've always converted pump discharge head to pressure using the outlet temperature/specific gravity. But with centrifugal compressors, I've used inlet temperature to convert head to pressure. Now I have a case where's there's significant temperature rise across a pump under...
