Vertical Centrifugal: Low Efficiency and High Motor Current Problem

Increased specific gravity of the fluid being pumped?

Check your incoming power quality.

Flow restrictions should decrease amp draw.

What maintenance has recently been done to the equipment?

Last maintenance was done in 2002, mainely worn parts are replaced like bearings, seals etc.

Perhaps you should shorten your maintenance intervals. Ten years seems a bit long.

Or, do you just wait until the pump fails to maintain it?

Was the pump originally operating acceptably, and if so, has anything happened to change the head value (including a change in specific gravity of liquid pumped)?

Maybe the impeller has slid down the shaft and worn itself significantly. Check the jam nut, if any.

If the flow is lower then less work is done, therefore the current would be lower.

Lower flow with higher current could mean you have a motor issue, or a volts/Hz problem

My money is on voltage AND maybe a worn impeller

You are facing two separate issues here : Low Flow and High Current.

Low Flow can be caused by one or a combination of several factors , viz - Cavitation due to suction problems ( hence the vibration & noise), the pump operating outside its efficiency curve ( head too high) , increased Head from design, drop in pump rpm, leakage at the Mechanical seal or Gland packing of the stuffing box and Worn out Impeller.

High Current is normally proportional to Flow, but in your case I do agree that it could be mainly due to an electrical issue, either in your starter system or in your motor directly. Alternatively, the Current could increase if the bearings that you have replaced have not been carried out properly and there is excessive resistance to movement of the pump shaft.

Hope this has been of some assistance.

I would bet on a head problem and look for some restriction in the pump's outlet.

You may please check whether there is any voltage unbalance problem of power supply feeding to the motor. Also please check the three line currents of the motor to see whether ther is any current unbalance. Due to voltage unbalance of power supply, beyond permissible limit, kW capacity of the motor is being de-rated, and as a result, the motor may draw more current than FLA(considering motor is fully loaded) if the load remains same.

Thanks,

Manindra.

Dear Mr Nadeem Lasi,

One possibility, Lot of Re-Cycling of the fluid, with in the pump casing, may take place due to high wear and tear. As for as the Impeller is concerned, if Re-Cycling is occurring. it is loaded fully, and on account of Re-Cycling, nett output flow is low. This inference is drawn from your reply statement that the pump is over-hauled in the year 2002.

In addition to this sediments also may get in to the pump - which you have not mentioned about this. Always sediments will weigh more in weight than the fluid, and needs more energy to pump.

What is the depth of the pump immersion in the fluid.? This has some impact on the working.

Thanks,

DHAYANANDHAN.S

One possibility, Lot of Re-Cycling of the fluid

This is exactly where my thoughts went. It may not be a pump problem at all, but possibly outside the pump such as a failed (open) recirc valve or relief located between the pump discharge and the flow meter.

It seems the simplest explanation.

Dear Mr. ChaoticIntellect,

Few years back, I came across a case, Re-Circulation from tip of the Impeller (where the pressure was high) the water entered the suction eye of the impeller. As for as the Pump Impeller is concerned - it is loaded, but out flow was less - thus power consumption was high and this is what I have referred in my reply.

Thanks,

DHAYANANDHAN.S

Good answer, I agree with your points, quite possible to happen.

To diagnosis further we need to know more details of the pump internals. A sectional sketch should be highly informative.

Again, I agree that the likely cause is some type of recirculation (either internal or external). The main point being that there is extra flow (accounting for the increased amps) and that the majority of the flow never goes through the flowmeter (accounting for the decreased flow).

For this case, the amount of recirculation is about half of the rated flow. From my experience, if the recirculation was internal, then for this relative magnitude of flow (half of the rated) there would be other indications such as audible noise from the pump, vibration, etc. which points me to an external cause such as an open valve (relief, recirc, bypass, etc) or a leak. It is important to note that many pump problems aren't due to the pump at all.

Without more specifics about the pump and system it is difficult to say.

I would hope the OP finds the cause and shares the experience.

Lets get the professionals in the mix here...

High motor current.. low flow rate!

First is the running current... higher than name plate? You don't state what it was and what is is now, just higher!

Second lower flow rate, how much lower? but you are getting fluid to surface? Yes? I know you have mentioned flow rates, are these the readings you have now, you were producing 237.6 m3/day or is that the pump curve you are quoting? For a problem like this and to bring it into this forum.. you got to be exact in your information

What is the depth? how many joints of tubing or in what is the fluid flowing in?

Could it be recirculating? possible answer, but in most cases you would not get much fluid to surface and the quickest way to prove that theory is the shut of the valve at the top of the tubing/outlet.. I am assuming that you have a pressure gauge there? If you shut the valve or are shutting the valve you should see the pressure increase with every turn, if the pressure is VERY slow to increase then yes. You have a hole on your tubing. Then you pull and fix it!!

If the pressure increases, but not to the max of the curve, you have a worn impeller and a further problem with the motor or something else that is giving you high(er) running current.

It was mentioned voltage in a previous comment.. again could be. Are you operating this pump on a VSD? If so who has played with it? Have you checked your supply voltage and Hz. We had a problem in Saudi where someone (that man 'someone' again) thought it was a good idea in summer to reduce the Hz on the Gas turbine gen set because of the A/C load, from 60 Hz to 49Hz, if you apply the rules of affinity... you can imagine how much oil production was lost until they found out the problem.

Go check you supply, go check you VSD, go close the well head valve or whatever you have at the outlet and watch the pressure gauge, and get back to me!

Best of luck!

and before I go... how difficult would it be to remove and replace?

a clogged pick up screen

PLEASE CHANGE MOTOR AND CHECK ONCE, IF PROBLEM DOES NOT ARISE THEN IT MIGHT BE MOTOR PROBLEM

could be an answer.. however, have you not thought about the cost implications to that suggestion.. and why change it if its running and producing at this moment? OK, its not giving the production required (based on OP's data).... it might run for another 6 months or longer, and that is one less change out that has to be paid for.

I would leave it run until it fails totally or the production is so lower, and then it must be pulled/removed/changed.. IMHO