Lubricity of pumped fluids 1

[11sas11]

I am trying to work out the lubricity of fluids that I am selecting a pump for, and if it will be a problem. The fluids are water, pentane, and R245fa. We have had some issues associated with durability using R245fa and I am not sure if it is due to flashing in the pump or just general lubrication. I can't seem to find any reference to how to calculate the results and I understand there is the ASTM D892 standard, but surely there are general results for various fluids?

I can get most of the physical properties for the fluids using REFPROP so can do reasonable calculations, but either my web skills are crap or there isn't much out there.

 

[EdStainless]

What kinds of pumps?
Temperature will be a critical factor.
In general none of these fluids has lubricity.
High purity water is the most difficult fluid that I have worked with.
PD pumps and valves were a nightmare working at 10ksi.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[11sas11]

Not hot and not high pressure.

As per the table

________________________Water__pentane__R245fa
°C ___ Temperature_______ 20______ 20______ 20
MPaA _ Pressure _________ 0.2 ____ 0.2 ______ 0.2
µPa.s Viscosity _________ 1002 ____ 231 _____ 430
kg/m3 Density __________ 998_____ 626 ____ 1352

 

[LittleInch]

Try a search for lubricity index or lubricity testing.

There are recognised tests which provide some numbers to compare different fluids.

Is a world of its own....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Lubricity is only relevant to screw /gear type or similar pumps. All the fluids you've listed wouldn't be suitable for screw/gear pumps. From what I recall, viscosity needs to be that of diesel or higher to use these pumps. This is common knowledge to PD pump vendors.

 

[11sas11]

Thanks @littleInch & @georgeverghese.

I did do a bit of a search but came up empty. Lots of reference books to buy or third party testers / machines. But no indicative data.

We are using a vane pump, but it has a mag drive and the bearings are lubriacted by the pumped fluid. As I mentioned we have had shorter than desired durability. The pump supplier indicated that they thought it was due to flashing. We run low NSPH (close to the limit), but from the logged data we never really had a problem during operation. I just don't want to send another pump back after 500 hours and have the warranty denied.

 

[georgeverghese]

If bearings are process fluid cooled, one can perhaps expect a 10degC rise in fluid temp between process fluid inlet and outlet for bearing cooling. Which implies that the process fluid must be at least 12-15degC away from bubble point temp (ie. subcooled) in order to avoid bearings from running dry.

Since all these fluids are single component fluids, we can then say that at the suction operating pressure, T_sat for the fluid - T_op > 12degC, where Tsat is the same meaning as bubble point temp.

We seem to continue getting bad feedback on mag drive pumps on E-Tips. At the least, in addition to the above, pumped fluids must be clean with ZERO solids.

 

[11sas11]

Thanks very much,

Yes we only run about 2K of sub cool going in. So adding 10K to that will flash at suction pressure. I was under the impression that the arrangement in the pump was that the bearing was after at least 1 pressure stage to avoid this.

It is interesting to note that there have been a lot of bad reviews on mag drive pumps. Our systems can't tolerate leakage so it seems like a good option. Perhaps it isn't as good as we first thought.

 

[georgeverghese]

"I was under the impression that the arrangement in the pump was that the bearing was after at least 1 pressure stage to avoid this."

Yes, the bearing cooling slipstream is taken from final discharge, but is throttled down close to suction pressure upstream of the bearings in most pumps.

 

[TenPenny]

As far as the comments on mag drive pumps, my thoughts after selling them for 20-25 years is, you do not want ANY solids in the liquid; you do not want to run dry at all, despite what some manufacturers claim they can handle; if the liquid can 'salt out' when shut down, such as salt solutions or sodium hydroxide, you need to flush the pump well at shutdown.

We had lots of them running well and for a long time, but there were some applications that just were not happy.

Fortunately, I'm retired now, so they aren't my problems.