3 different points on pump curve...not adding up?
3 different points on pump curve...not adding up?
(OP)
Hello,
I have 3 vertical sump pumps at our plant. I've been having trouble finding where it runs on its curve and need some advice. I took amp readings (converted to bhp), NEW gauge dP readings, and downstream flow meter readings, and none of the points really line up on my curve. Any hunches on what this could be? Air entrapment/vortexing? Dirty suction?...etc? Any advice or tips would be great for a young reliability engineer. I can provide more information if needed.
Thanks!
Frank
I have 3 vertical sump pumps at our plant. I've been having trouble finding where it runs on its curve and need some advice. I took amp readings (converted to bhp), NEW gauge dP readings, and downstream flow meter readings, and none of the points really line up on my curve. Any hunches on what this could be? Air entrapment/vortexing? Dirty suction?...etc? Any advice or tips would be great for a young reliability engineer. I can provide more information if needed.
Thanks!
Frank





RE: 3 different points on pump curve...not adding up?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 3 different points on pump curve...not adding up?
Do you want this problem solved or not? The least you could do is point us to your previous posts on this.
http://www.eng-tips.com/viewthread.cfm?qid=408029
http://www.eng-tips.com/viewthread.cfm?qid=407067
Good luck,
Latexman
To a ChE, the glass is always full - 1/2 air and 1/2 water.
RE: 3 different points on pump curve...not adding up?
RE: 3 different points on pump curve...not adding up?
Note that the pump has an efficiency separate from the motor efficiency.
What accuracy are you expecting? How close is it to the curve? 1%, 2%, 50%? How big of a pump are you talking about?
RE: 3 different points on pump curve...not adding up?
RE: 3 different points on pump curve...not adding up?
RE: 3 different points on pump curve...not adding up?
After several embarrassing incidents, I made it a policy to only trust data that I personally measure, or observe _very_ closely.
Mike Halloran
Pembroke Pines, FL, USA
RE: 3 different points on pump curve...not adding up?
Check the inlet strainers, check for vortexing / pre- rotation at the inlet, air entrainment, carefully measure flow / head / power with 1 pump operating then 2 and then 3 - report or better still plot 3 curves, advise all relative levels, sketch the layout, supply the original data info for the installation. From this data there is a chance we can see the problem, maybe request some meaningful extra data to make understandable recommendations.
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.)
RE: 3 different points on pump curve...not adding up?
Suction screens were relatively clean, however there is a chance the pumping chamber has a layer of mud on the bottom that isn't necessarily sticking to the screens yet still causing suction issues at the bottom. I am working to get a vacuum truck in here to pump out the chamber.
Here is the pump curve
Here is the piping layout. Disregard the flow and pressure readings here... Note there are actually 3 pumps that feed into one common header right when they come out of the sump. One is the primary, second kicks on during high level (>60%, maintains 30%), and third is a inline spare.
RE: 3 different points on pump curve...not adding up?
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.)
RE: 3 different points on pump curve...not adding up?
Ideas like are mag flow meters good indicators if air is present in the line? Or other debris?
Vortexing possibly causing issues.
How accurate are typical motor readings?...etc.
Just was interested in any ideas or experiences people have came across to attack the problem efficiently.
RE: 3 different points on pump curve...not adding up?
Some basics.
I can only assume that you have the right pump curve for the pump you're looking at. Is it the 9.5" curve we're looking at
Questions - You said in an earlier post " I did install the re-circulation line as referring to those old posts. " Where is it on your sketch? How much flow is going through it.
Is this the test curve for that pump or a "generic" one? They can be 10-15% different from reality.
The immeadiate thoughts I have are:
Based on your sketch and reading of 20psi, the differential head across your pump appears to be about 55 ft. The intersect with your curve would then give a flow reading of about 1500GPM and a shaft power requirement of about 27 hp. So something a bit odd there alright - i.e. where is that flow going?
If your flow rate is correct (275gpm) and you're operating on the far left of the curve then differential head and pressure at your guage position should be much higher.
So maybe your inlet is clogged, the impellor coated in mud, something wedged in the discharge, you impellor is eaten away or your readings are not where you think they are. Possibly rotation (has anyone checked?), voltage at the motor is higher than 480V?, shaft or bearings not lubricated?
Anything more you can give us?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 3 different points on pump curve...not adding up?
http://www.pumpsandsystems.com/topics/pumps/centri...
Which of the pump impellers is installed on the pump.
RE: 3 different points on pump curve...not adding up?
Good luck,
Latexman
To a ChE, the glass is always full - 1/2 air and 1/2 water.
RE: 3 different points on pump curve...not adding up?
All of these data points were taken with re-circulation line closed. The whole reason for the initial re-circulation line was a quick and cheap way to protect the pumps before we can get another project for VFDs implemented (already have done analysis on this capability). It was believed that the fundamental issue with these pumps are that during 95% operation they operate around 300 GPM which is basically at min flow. But now I am starting to second guess the readings from the flow meter. Interestingly, the pump seems to be happy when the discharge gauge reads about 20 psig.
I had a 3" recirculation line put in, but just have the valve slightly opened now. Opening it too much cavitates the pump and the discharge gauge drops to about 11 psig ish (which makes sense on the curve). We tried to get exact flow reading but due to air in the line.
Bearings/shaft are lubricated and voltage is definitely 480, rotation has been confirmed as well. If something was wedged in the discharge wouldn't that create a higher pressure on the gauge due to back pressure?
Thanks again everyone.
RE: 3 different points on pump curve...not adding up?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 3 different points on pump curve...not adding up?
RE: 3 different points on pump curve...not adding up?
What does this pump inlet actually look like? If the bottom of the sump is full of crud then your pump might be inside a sump of mud causing friction losses or more vortexing than you would normally expect.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 3 different points on pump curve...not adding up?
RE: 3 different points on pump curve...not adding up?
Check this link
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 3 different points on pump curve...not adding up?
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.)
RE: 3 different points on pump curve...not adding up?
RE: 3 different points on pump curve...not adding up?
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.)
RE: 3 different points on pump curve...not adding up?
RE: 3 different points on pump curve...not adding up?
Good luck,
Latexman
To a ChE, the glass is always full - 1/2 air and 1/2 water.
RE: 3 different points on pump curve...not adding up?
RE: 3 different points on pump curve...not adding up?
Good luck,
Latexman
To a ChE, the glass is always full - 1/2 air and 1/2 water.
RE: 3 different points on pump curve...not adding up?
RE: 3 different points on pump curve...not adding up?
RE: 3 different points on pump curve...not adding up?
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.)
RE: 3 different points on pump curve...not adding up?
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.)
RE: 3 different points on pump curve...not adding up?
Even 2 months later.
Thanks LI.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 3 different points on pump curve...not adding up?
RE: 3 different points on pump curve...not adding up?
For me this would be:
Levels and vertical measurements - t's difficult to misread a tape measure.
Pressure gauges / transmitters (easy to calibrate off line) - make sure you're at between 30-70% of range for best repeatability
Amps are fairly standard as are volts so you can be pretty sure about those, but again could be removed and calibrated or duplicated if you want to be sure.
Flowrate is a little harder to be certain of, especially if there is air involved. Any chance you could set up a single pump divert to a known volume tank and measure volume over time, then switch back to the main line?
The latter would also let you know if there is air entrained as well.
Good luck!
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 3 different points on pump curve...not adding up?
1. One thing I have noticed is, you have 8" line and pump and have only 4' submergence (which could be even smaller) inside suction tank. Is you pump not big for its application?
2. Your flow meter reading could be not correct, due to half flow or low flow.
Curtis
RE: 3 different points on pump curve...not adding up?
1. I believe 4' submergence is more than adequate for a vertical sump pump. What are you calculating it at?
2. And that may be true but it its low flow that doesn't match up with the discharge pressure I am getting either...