Suction Design Pressure

[maintennance]

In the Process Data Sheet, "Suction Design Pressure" is indicated. It is being insisted that we have to take this value as "Max Suction Pressure" for our pump selection and shutoff head calculation. We are not convinced. We argue that the term Suction Design Pressure is only for the design purpose of the suction pressure system ( pipelines)and need not for the Pump.This also sometimes overdesign the mechanical seal assemblies for higher stuffing box pressures if Suction design Pressure term is to be considered as Max suction pressure. Thanks to clarify.

 

[zdas04]

It is your Process Data Sheet. The answer should be available within company standards or you should make up your own definition and include it with the Data Sheet. I've seen people effectively de-rate a system with ANSI 600 flanges to the maximum allowable suction pressure of a pump, and I've seen people take the approach that the maxumum suction pressure is not relevant to pipe design (I had a hard time with that one).

David

 

[CH5OH]

normally for the suction side of the pump you would use NPSHA (netto posive suction head available)which is defined by the proces data and NPSHR (...required) which is defined by the pump data.
suction design pressure would be the pressure the pump will see at his suction side.therefore its important to specify the pump (design pressure pump=suction pressure+shut off pressure+safety margin)
example:
pumpdata:
shut off pressure=10bar
design pressure=12bar
case 1:
suction design pressure=1bar
above pump will suffice
case 2:
suction design pressure=50bar
you dont want to be around, when they take the pump in service!lol

 

[BigInch]

Maintennance,

"Design" could mean an operating condition, or it could mean an "absolute maximum condition" during some emergency situation. If I saw it without any further explanation or other listed values, I would assume that "design suction" is indeed an absolute maximum value, but I have also seen much confusion on the topic.

As zdas says, talk to the chief engineer and get some definitions into a company standard that everyone can live with and know very well what they mean.


**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[rneill]

Are there two separate issues here?

1) the process design of the pump - that is, it's capability to achieve the specified discharge pressure and flowrate when considering the actual range of suction pressures that it will see

2) the pressure for which the pump suction system is to be designed to ensure mechanical safety and that neither the suction piping nor the pump suction will fail.

It seems to me that issue 1 is solely concerned with the realistic range of actual operating suction pressures and that issue 2 is where we would be concerned with what has been specified as the "suction design pressure" and with at what pressure the suction side protective systems (relief valves) were set. Issue 2 involves code/regulatory compliance and I'm not sure we would care whether the pump was performing as intended at this condition, just whether or not we had a breach of the pressure containing envelope to deal with?

My thoughts anyway

 

[MikeCool]

They are insisting on MAX suction pressure because they want to make sure the pump is suitable to achieve MAX discharge pressure without breaking. Max dischare pressure includes max suction pressure. Your design suction pressure is ALSO required for properly selecting a pump to achieve desired performance. Your pump engineer needs both values. He/she should also ask, "what is the LOWEST suction pressure you might see?" If he/she doesn't, talk to his/her boss.

Mike Cool
Mechanical Engineer
American Stainless Pumps, Inc.
Los Angeles California USA

http://www.aspumps.com