Design Pressure for Screw Pumps

[1ton]

I was recently made aware for high pressure screw pump. The design pressure of the inlet and outlet side is different. Example if the design of the discharge side is 80bar, then maybe be the suction side is design at 40bar. Is this a common practice, for screw pump manufacturer. API std doesn't seems to cover this.
Any thoughts on the advantage and disavantage of such design.
Thank you
1ton

 

[MikeHalloran]

The screw pumps with which I'm familiar are run with the inlet supercharged, by means of a pressurized reservoir, typically at 4..5 bar. They run at a discharge pressure of 200 bar.

Regulations and standards aside, if there's no circumstane in which the inlet could be pressurized to the discharge pressure level, a little asymmetry could produce a modest weight savings.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[checman]

Most pumps by design have inlet pressure limitations but they normally do not come into play. The limitations come from different components of the pump or its design. One component that gives limitations are mechanical seals. Seals may see full suction pressure plus a percentage of discharge pressure. Internal pressure relieve valves may see suction pressure as a closing force and might need to limit the suction pressure to keep the pump from exceeding its maximum pressure. The working side of the pump is normally the discharge and bearing thrustloads are designed for predominate thrustloads to come from the discharge. High inlet pressures can throw this out of whack and is a key factor in the amount of damage you will get from water hammer on end suction centrifugal pumps. AOD pumps do not like high inlet pressures at all. You will have short diaphragm life and you may bend the pump shaft. All I am saying is that most pumps do have suction limitations but many can be designed for higher pressures if needed.

Regards checman

 

[unclesyd]

You might want to go over this site as the have a variety of screw pumps even the granddaddy of them, the Sier-Bath.

http://www.fpdlit.com/cms/results_detail.asp?ModelID=118

They also have the Cameron Hydraulic Data Book $39.50

https://www84.ssldomain.com/fpdlit/Merchant2/merchant.mv?Screen=SFNT&Store_Code=CHDB

 

[rzrbk]

Although a pump with a suction end fully rated for discharge pressure would be preferred, it probably saves some expense by reducing wall thickness, flange rating, etc.

The disadvantage would be that if some other pressure source exists, such as backflow from downstream or from the spare pump, then an overpressure protection would be needed in case the suction block valve was closed with the discharge valve left open. A PSV on the suction piping may be needed, or this may be able to handled procedurally (eg car sealing suction valve open, etc).