"Compression Ratios" for pumping liquids 1

[zdas04]

In compressible flow we use the very useful concept of "compression ratios" as a shorthand notation for the ratio (in absolute terms) of a compressor discharge pressure to the suction pressure. This ratio has significant physical characteristics in addition to being very concise for communications.

When talking about the differential head in a pump, does anyone know of a similar widely used term? When I talk about a centrifugul pump operating at 2-3 "ratios" per stage I get a blank stare because "ratios" implies "compression ratio" and most liquids are largely incompressible at low differential head. Calling it a "lift ratio" gets me even more blank stares.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

 

[pmover]

to simply state, when dealing with pumps, terms used are head or head/stage, expressed in feet or meters of water and flow expressed in gpm, lps, gph, etc.

i would definitely have a quizical or questionable facial appearance and would ask for clarification.

regarding gas compressor terms, your statements are understandable.

good luck.
-pmover

 

[PUMPDESIGNER]

pmover has it correct.


PUMPDESIGNER

 

[aberta]

Thanyou Zdas04 for your question. It has helped me very much.

 

[MortenA]

David

The reason why you talk of compression ration with gasses is that this is fairly constant with no regards to initial pressure but only for a limited inlet pressure range.

For a pump however the HEAD (as it is called) is constant when measured in height of liquid collumn - regardless of inlet pressure and medium. Providing that the casing dosnt burst i has the same head regardless of the inlet pressure beeing 1 or 10 barg.

The head is allways the same regardsless of liquid properties - but the outlet pressure (or even perssure rise) is no: Eg a pump with a head of 10 m (at a given flow rate) and a inlet pressure of 0 barg will have a outlet pressure of 1 barg when pumping water (density=1000 kg/m3) but out 0.8 barg if pumping a oil with a density of 800 kg/3m)

Best regards

Morten