Hight Temp & High Suction P - effect on performance? End suction centrifugal 1

[TenPenny]

Just looking for thoughts based on experience.
We have an end suction ANSI pump, 2x3-8, if that matters. On the test bench, we get performance close to the factory curve, using cold water (15C), suction pressure 4psig.

In the field, the exact same pump with the exact same clearance (nothing was changed), running with 145psig suction pressure and 355F water, the performance is approx. 10% less (as in, let's say at 140 gpm flow rate, on the bench we get 320 ft head; in the field with hot water / high suction press, we get 293 ft).

Obviously, these numbers are adjusted for the SG of the hot water, but is there some other reason that, with the same speed, same impeller, same clearance, and same flow rate, we would get lower head? One would almost think you'd get better performance at the higher temp, as the clearance would tighten up when the pump heated up.

Scratching my head, wondering if it's time for a drink yet.

 

[rotw]

are you testing the pump with its job motor ?

 

[Artisi]

A few thoughts for review.
Not really my area -- but,
Same motor?, if different motor did you check speed?
How about viscosity changes?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[JJPellin]

With suction pressure that high, the thrust direction on the rotor is probably reversed (thrusting toward the coupling). If the end float on the thrust bearing was set too high, the shaft would thrust away from the suction and open up the face clearance on the impeller. I would verify end float. I don't work with ANSI pumps very much, but we set our thrust float to 0.002" to 0.004" with a back-to-back pair of angular contact thrust bearings. I am sure you would have considered hard cavitation as the source of the lost head. But, in water that hot, it should be obvious to anyone close by that the pump was cavitating. New installations often have temporary start-up strainers. If there is a start-up strainer, I would remove it and check for solids.

Those are the items that occur to me.

Johnny Pellin

 

[LittleInch]

I didn't realise how much viscosity changed with temperature so I would say it is viscosity related in some way.

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

 

[TenPenny]

Hadn't thought about viscosity, that's definitely worth investigating.
And the thrust issue is worth checking, it's a brand new pump, but still, will dig into it.

that's why I thought i'd throw it out here, to get the experts thoughts.

As to the motor, the speeds were verified with a strobe, and the test bench set at the speed measured in the field, so that's not the issue.

thanks for the ideas

 

[mk3223]

For the service temperature of 60F vs 355F, the water SG is changed to less 1. It could be an impact to the pump performance at the elevated temperature.

 

[ashtree]

I agree with all the comments made so far but nobody has mentioned the materials of construction. Whilst you might expect all the tolerances to tighten up and pump performance to be maintained or improved, what might happen if there are several different materials used in the pump. Is it possible that due to different expansion co-efficients from different materials that some critical tolerances have worsened. I am thinking here particularly around the impeller eye area.
Without any details on the system is it possible that flow metering and pressure measurement etc is inaccurate at 355F and the pump is actually going okay.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"