Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

Register Log in
  • Congratulations IDS on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Pump running in SF 4

Status
Not open for further replies.
itsmoked

itsmoked

Electrical
Feb 18, 2005
19,114
10hp down hole centrifugal pump.
New.
Set at about 70 feet.
Pressure measured and found at center of BEP.
Rated flow 90g/min.
Actual measured flow 85g/min.
230V 3ph.
Supply voltage 241V - all phases within 0.5V
Wire size from measured point to pump 6AWG.
Rated current 30A
Actual current [red]31A,31A,34A[/red]

Why?


Keith Cress
kcress -
 
Replies continue below

Recommended for you

Sort by date Sort by votes
Without getting too academic I would say the motor is overlaoded or near to it - assuming it is 10HP as you advised in the first posting (or is it a 15HP motor) a 10HP would be too marginal on this pump unit.

[140 x 2.3] + 10 x 90 / 3960 / 0.72 = 10.5 HP

 
Upvote 0 Downvote
BigInch,

Thanks for so nicely restating my point. The system curve is very important for designing a pumping system or a control system. After it is built, if the question is asked (as it was in this post) about the performance of the pump, I have no need to generate a system curve. I simply need to know the suction and discharge conditions, the product properties and the flow rate. And, you also quite nicely pointed out the relative importance of the system curve to a pipeline application (your expertise).

I make comments regarding my industry (oil refining). We almost never have a single pump that pumps different products at different times. We almost never have to consider the pressure up and over a hill. I have been analyzing pump performance in an oil refinery for almost 22 years. I am not being lazy or stupid. My industry is different than yours. The particular question that was stated was one of pump (and motor) performance, not system design. If the result of the first question was to say that the system was not correctly designed, then we could have a lively discussion about the way it might need to be redesigned. Instead, Artisi quite correctly stated the correct answer. The pump should be expected to require more than 10 HP at the published pump efficiency. The fact that the motor is drawing over full load amps is not particularly unusual or surprising given the data provided.


Johnny Pellin
 
Upvote 0 Downvote
Artisi - can you explain where you came up with 140 ft head?

=====================================
(2B)+(2B)' ?
 
Upvote 0 Downvote
JJ Sorry if I seemed condesending. That was NOT my intent. I realize that we do tend to see things from our industry's perspective, which is exactly why I provided another one. Other than that, I can assure you that I never cease to be amazed at the depth of your knowledge concerning pump, characteristics, internal design, repair and their ops and maintenance (and that's the short list). I've been a dedicated fan of your's since the first time I read one of your posts and never missed one since. I really thought I was directing my comments to others that may be reading this thread, that might have been left wondering what possible use system curves might have.

"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.

"Being GREEN isn't easy." Kermit[frog]
 
Upvote 0 Downvote
10.5hp would certainly fit the problem.. Yuck!

The chart:
6nnby5r51c.gif




This pump is below the curve. How does that square with the the 10.5hp?


----------------------------------


OK, You have a pump down the hole. Once you power it up you find the working pressure puts you below the curve a tad yet we're over working the motor.

If we throttle until we drop to 29A we seem to closing the valve down to about 20% of open - which is hideous.
Seems a waste to pull the whole string, return the motor and replace it with a 15hp which will be overkill.

What solution would you guys reach for here?



Keith Cress
kcress -
 
Upvote 0 Downvote
Don't forget to add the height from water level up to ground level or where ever you are measuring the 140PSI which seems to be 10ft ie, pump set at 40ft with 30ft of water over the pump. Total head on the pump is probably round 335ft and you have to consider that the pump may not actually reach the published curve for a number of reasons which could lead to another discussion.
 
Upvote 0 Downvote
You're more or less right on the money with that 140 psi at 90 gpm; I get 10.3 HP when corrected for pump eff of 0.72

Its doubtful that there is anyting wrong with the pump or the installation. Start looking at the motor. RPM is probably close, so its something in, ... or not in, the elect circuit.

"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.

"Being GREEN isn't easy." Kermit[frog]
 
Upvote 0 Downvote
Think we are splitting hairs, without very accurate flow and head figures which are actually irrelevent in this case I think it is fair to say the motor power is certainly telling us that the installed duty for the pump is in excess of the motor capability.
 
Upvote 0 Downvote
So you guys can offer no suggestions for reducing the load on the motor by 2%?

If we throttle it don't we just trade higher head for lower flow? Which won't probably help.

What if we raise the pump so it has 10 feet less suction head?
Of course then we have 10ft less pumping head so the flow will rise..
24e5jx1.jpg


Keith Cress
kcress -
 
Upvote 0 Downvote
The pump seems to be performing as designed. The one high current leg I have found to be common on open deltas. You are running at 1.1 times the motor FLA, or at worst case 1.18 times. The motor service factor is 1.15 and that is with 95-degree F surrounding water. If this is ground water, and even better, if the supplying aquifer is below the pump setting, the motor is well below the max. design temperature. I have found pre-engineered (no-engineered?) off-the-shelf pump/motor combinations to be often guilty of running well into the motor service factor. Grundfos is a prime example, especially in their multi-stage can style pumps. It is interesting that the “pump curve” does not anywhere show horsepower. I would let it run.
Steve
 
Upvote 0 Downvote
Keith,

The motor doesn't give damn about the current. It cares about temperature. If the fluid temperature is lower than that used when determining the rating then the chances are the windings are cooler than at rated conditions, and the motor will be ok. Might you be chasing a non-problem?

Anyway, if the motor is going to die because a 2% overload at rated conditions then it must be either Italian or Chinese. [smile]


----------------------------------
image.php

If we learn from our mistakes I'm getting a great education!
 
Upvote 0 Downvote
2%? sure. Throttle it if you don't mind a lesser flow. Even though head will rise, the proportion of head increase with each decrement in flow is such that power consumption will also fall off.

"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.

"Being GREEN isn't easy." Kermit[frog]
 
Upvote 0 Downvote
The motor is made in Japan and the fluid end is a Goulds. I believe the problems is with the manufactueres. In the well pump industry every manf. is trying to out do the others by saying that their fluid end can pump more water for a given hp. All the manf. load the motors into the service factor. I would guess that the original poster is a little off on his numbers.

In this industry if you want a pump that does not work in the service factor, you have to specifically order a n.o.l. pump. The good thing is that all the motor manf. know this and plan on it when they design a motor.

My other concern it the pump is below the curve. Was this a new pump?
 
Upvote 0 Downvote
NOL non-over-load.

IMO this below the curve is a red herring thing. There is nothing particularly bad indicated by a difference of only 2% between a site installation calculation and a test bench curve, especially since I think that we still do not know the height of the water level over the pump.



"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.

"Being GREEN isn't easy." Kermit[frog]
 
Upvote 0 Downvote
I don’t have the little Post-It I did my calcs on, but I think we had 30 feet of water over the pump and a setting of 40 feet. That makes the TDH 10 feet plus 140 PSI plus ? If this is a municipal system or even an industrial install, it is common to see one or two spring loaded checks installed just above the pump. I think the pump is hitting the curve very well.
Steve
 
Upvote 0 Downvote
the curve is from the mfg. catalog, this was apparently not bench tested. We have not seen the actual pump curve. Could it be possible that the pump is not performing as advertised [ponder]
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

Mike9208
  • Locked
  • Question
Centrifugal pumps running in parallel, one pump with high vibration
2
Replies
25
Views
803
EdStainless
EdStainless
Inchtain
  • Question
Industrial Pump Incident
Replies
5
Views
2K
georgeverghese
georgeverghese
balasub
  • Question
Pump Efficiency limitation
Replies
13
Views
3K
pierreick
pierreick
dogboy74
  • Question
Dust/debris in my vacuum pump lines 2
Replies
14
Views
464
Artisi
A
B
  • Question
Centrifugal Pump - Priming
Replies
14
Views
5K
LittleInch
LittleInch

Part and Inventory Search

Sponsor

Back
Top Bottom