Pump Efficiency
Pump Efficiency
(OP)
Folks,
We have 6 vertical turbine pumps (3 stage) which are rated at delivering 4400 gpm. From commissioning, which was approximately 9 years ago, the pumps delivered around 4300 - 4400 gpm. Fine. Recently, we have seen the performance drop to 3900 - 4000 gpm, around a 10% drop in performance. We have serviced these pumps, checked all wear ring clearances, runouts, bearing bushing clearances and checked for any casing leaks. We did everything I think could possibly be done, yet the pump isnt delivering much more, around the same 4000gpm. A Process consultant on site is adamant that the pump is still the problem no matter how hard I try to explain to him the pump is governed by the system it's in and that will dictate where on the curve it operates. The pump pumps into RO membranes which can become, clogged, fouled or damaged. I would like to get your opinions, do you think it is a system problem as I think or am I not addressing some issue with the pump. The only proof I have that it's the system is that I know for a fact that I've checked everything regarding the pump and I dont see anything else that can be done - pump was fitted with new shafts, sleeves, bushings and clearances are in spec.
We have 6 vertical turbine pumps (3 stage) which are rated at delivering 4400 gpm. From commissioning, which was approximately 9 years ago, the pumps delivered around 4300 - 4400 gpm. Fine. Recently, we have seen the performance drop to 3900 - 4000 gpm, around a 10% drop in performance. We have serviced these pumps, checked all wear ring clearances, runouts, bearing bushing clearances and checked for any casing leaks. We did everything I think could possibly be done, yet the pump isnt delivering much more, around the same 4000gpm. A Process consultant on site is adamant that the pump is still the problem no matter how hard I try to explain to him the pump is governed by the system it's in and that will dictate where on the curve it operates. The pump pumps into RO membranes which can become, clogged, fouled or damaged. I would like to get your opinions, do you think it is a system problem as I think or am I not addressing some issue with the pump. The only proof I have that it's the system is that I know for a fact that I've checked everything regarding the pump and I dont see anything else that can be done - pump was fitted with new shafts, sleeves, bushings and clearances are in spec.





RE: Pump Efficiency
If the pump has been completely overhauled and it is ok, I would be inclined to think of a system's problem.
RE: Pump Efficiency
RE: Pump Efficiency
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pump Efficiency
RE: Pump Efficiency
Are the flows you gave determined pump by pump individually or taking the flow of all pumps in parallel and dividing by six?
Can you post the original TDH and the current TDH.
Any build up in the pit near the pump suction(s)? Any change in the pit level?
rmw
RE: Pump Efficiency
if yes, rpm still the same?
if no, you might have internal leakage (between stages or from discharge to suction)
if the proces is to blame, you should see a difference in discharge pressure (unless the pump curve is really flat)
less flow means higher discharge pressure
RE: Pump Efficiency
Is there any changes in the inlet supply level, have the RO elements been changed or is there any likely head change after the RO unit/s
RE: Pump Efficiency
If the water is not demineralized, it could be prone to lime buildup in the piping. I have seen 10 inch pipe with only about a 4 inch hole left down the center in very hard water services.
Are you sure that the flow measurement is correct. If it measuring a pressure drop across an orifice plate, the plate could be washed out resulting in an artificially low reading. Has the flow meter been calibrated? Has the orifice plate been inspected?
Johnny Pellin
RE: Pump Efficiency
Mark Hutton
RE: Pump Efficiency
Mike Cool
Mechanical Engineer
American Stainless Pumps, Inc.
Los Angeles California USA
www.aspumps.com
RE: Pump Efficiency
RE: Pump Efficiency
RE: Pump Efficiency
I agree with the earlier posts that the suggest that the problem is probably within the connected system and not in the pumps, but you didn't mention anything about the pump motors or the electrical supply. If there have been any electrical supply changes (other greater loads on the same supply, different supply transformer, etc.), or the motors have been rebuilt, re-wound, or replaced, then it is possible that the pumps may actually be operating at slightly lower shaft speeds resulting in slightly reduced performance without any significant physical changes or degradation within the pumps themselves.
You didn't mention any sort of VFD, so I'm assuming that the nightmare of VFD's and multiple pumps is not a part of your problem. If VFD's are involved, then there is a really big can of worms to deal with.
RE: Pump Efficiency
BigInch and MikeCool pointed out the issue. You are only looking at 1/2 of the info....FLOW. A pump curve is defined by 2D points. Flow AND head.
When that pump was brand new....you could have run the system...choked down a valve...adding friction...and pushed the pump back left to a lower flow. Would THAT have been a pump problem?
No. Operations personnel...and more than a fair share of engineers make this mistake. To judge a pumps performance...you have to look at flow head points...not just flow and heads alone.
Run a real pump test. Measure flow and head at each point. This requires good pressure gauges on suction and discharge. Correct for gauge elev...and don't forget to calc velocity head (though that should not matter much in a high head application).
RO pumps are high head...so your pump curve could be flat. That means a small change in friction (membrane 'gunk') could push you left quite a bit. I would be that you are requiring the pumps to work against more pressure...pushing your point left.