4 replies to this topic

[JEBradley]

Im looking to pump heptafluoropropane - dynamic viscosity of 0.2442 cP and a density of 1386 kg/m^3

Ive just been told by a pump supplier that they cant quote because the viscosity is too low. I would generally think that having a low viscosity fluid is a good thing - can anyone suggest possible problems caused by low viscosity (aside from the obvious one that this guy won't sell me a pump!) Im wondering if im missing an important point here??

[pleckner]

You may be missing a very important point.

What type of pump are you looking to use, Centrifugal or Positive Displacement (PD)? PD pumps don't like low viscosity fluids.

Can you share the make of pump you were inquiring about?

[JEBradley]

Well it is a PD pump!!

The exact pump is an internal gear pump

http://www.anchorpum...ikingpumps.html

I have thought of several factors that MAY be a problem but nothing that im convinced with - some kind of internal recirculation seems to be the best thought so far.

Thanks in advance

[latexman]

Yes, internal by-passing. While the pump is new it may pump okay, it may not, but as the clearances wear it'll by-pass more and more and more until it won't meet the duty.

[pleckner]

Look at piston pumps, diaphragm pumps or even rotary lobes instead. Fristam rotary lobes can be designed to handle low viscosity liquids but they are also relatively expensive.

Having a large back pressure against the pump will also help.