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high Amps on newly replaced pump

high Amps on newly replaced pump

(OP)
hello,

I just had a non-seal centrifugal pump replaced with newer one as the old pump was obsolete after almost 20 years of service, its used in a high temperature application and the new pump is almost 100% exactly the same specs of the old pump, just the new model from the manufacturer with newer bearing monitor (digital), tested with ambient temp glycol instead of 205, however that is not the issue because if you calculate the head at the density at this temperature it will not still lead to this number in power and hence to current of 6 amps...

the pump sound is quite, nothing looks abnormal, however its drawing 6 Amps of current instead of its stated in datasheet of full load of 5.2 Amps, which causes the breaker to trip as the set point is 6.2 amps, I know that we can increase the set of the breaker but that is not the case, why would it take higher current?

direction of rotation is correct (shown in digital monitor panel of the pump), both radial and axial bearings indicates very well condition.

any clues?

pump info: suction 2 inch , discharge 1 1/2 inch
suction pressure = 0
discharge pressure 2.94 barg
rated BHP (KW) = 1.34
Max BHP (KW) = 1.79
pumping temp = 205 C
sp gravity @temp = 0.98

RE: high Amps on newly replaced pump

Non-seal means what?
Almost 100% - so what is not 100% - slightly higher flow, slightly less efficient?

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: high Amps on newly replaced pump

(OP)
non-seal is another way of writing seal-less pumps, its canned type centrifugal pump, I hope this answers this part

in fact its almost 100% because the new pump has got higher efficiency 41% compared to 34% of the old one.

RE: high Amps on newly replaced pump

You need a copy of the pump curves to check where the previous pump was operating and compare to the new pump. It could be this pump is operating further out on the curve, as Artisi suggests, thereby consuming slightly more power. Bit hard to tell without all the facts.

RE: high Amps on newly replaced pump

(OP)
I did that already, and I can assure you that nothing has changed in operating parameters and the new pump ordered in accordance with that, the effect of slight change in density due to lower temp had almost minimum effect when checked on pump curve and corresponding power (no amps in their curve so I just converted via V*I*cos@ ) , its almost an identical replacement, so what is the reason for high amps?

thnx

RE: high Amps on newly replaced pump

We need a copy of both curves and full operating conditions, flow, head,pump speed etc- otherwise it's all guess work.

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: high Amps on newly replaced pump

OK, to try and make sense of this what we need is

Please humour us and post the curves and copy of the test results for the pump (you stated it had been tested) and also test results for the motor (if available/).
What does 6 amps represent in shaft power?? Need to know running voltage at the motor and efficiency of the motor

Flowrate

Also are those values you quote measured or from the data sheet?

Options for excess amps include many of what you have apparently checked but also:
Your motor voltage measured across the terminal isn't what it says it should be - needs electrician to check when running
There is something extra rubbing on the pump shaft

This is a small pump and motor so often the variances in either pump or motor from the data sheet / brochure can be significant. As can be any small mechanical issue.

Await further info.

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

RE: high Amps on newly replaced pump

(OP)
ok first of all many thanks for the replies
@Littleinch , as for running the motor solo, I have mentioned that its canned motor type, there is no chance for dis-coupling this, and there does not seem to be any indication of abnormality during operation, its quite, both radial and axial bearings are giving healthy lights, and for current it was checked by electricians and confirmed to read 6 instead of 5 or below. the rating of the motor is 1.7 KW.

the curves are attached as requested,

regards,

RE: high Amps on newly replaced pump

Mystery, the new pump should be drawing less current than the older unit assuming the thru'put in terms of flow and head are the same.
Can you verify the output of the old unit compared to the new unit in real terms -not hearsay or wishful thinking,

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: high Amps on newly replaced pump

OK, so the pumps at their duty point are quite similar.

SO what about the other things?

Have you actually measured flow?

Strikes me the new pump has a larger capacity so it may be that whereas the old pump might have been working at the end of its curve and the head dropped off, this new pump will maintain a higher head resulting in more flow and hence use more power?

Also you mention glycol - have you allowed for the difference in viscosity in the pump curves? might be very low, but you have only a fine margin here.

Also is that new pump curve just what the vendor supplied or was it actually tested?? before being installed? Can you alter discharge pressure / flow to do your own test and check the actual pump curve versus the one supplied by the vendor?

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

RE: high Amps on newly replaced pump

The newer pump should have a higher efficiency motor which runs at a different rpm than the old motor. Because of this, the flow will be greater than the old pump and require more amps.

Do you measure the actual flow?

RE: high Amps on newly replaced pump

bimr makes a good point, a 20 year old motor of this power could run at speed a fair bit less than a current motor - it needs checking - but I would have thought the supplier would have picked this up and sized the impeller to suit the supplied motor. However speed and diameter are not shown on the curves.

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: high Amps on newly replaced pump

  1. Is this a 3 phase motor?
  2. What is the voltage rating of the motor?
  3. What is the actual voltage? Check voltage phase to phase and phase to ground?
  4. Are you sure the impellor is cut to what the curve says? Easiest way to check it is to do a shut in head test or you can open the pump and measure the impellor diameter (this is a small pump). Is it the same as what the curve says?
  5. What is the efficiency of the motor?
  6. Your electricians can only measure shaft power. Therefore your actual bhp will be (shaft power * motor efficiency). Convert this into WATTS
  7. Remember that for a 3 phase motor POWER (WATTS)= 1.73 * VOLTS * AMPS
  8. Plug in the numbers to see if it makes sense and use the information you gathered from all of the above to come to a conclusion. By using this method you can actually determine where you are running on the pump curve winky smile

RE: high Amps on newly replaced pump

are we talking about a 2kW or 2000kW, just get real and have a good look at what is what - check flow and head against what you think it should be -you have given Q and H for the pump requirements but have not given any actual operating figures - you are just running around in circles spinning wheels without any chance of a meaningful answer.
Come back with something that's actual and measured if you want answers.

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: high Amps on newly replaced pump

(OP)
Thank you all for your replies, I will try to answer all the question to help you help me :)

@Artisi : yes you are right and both datasheets agrees with you , old pump motor is 2.2KW (2200 watts) Synchronous speed is 3000 rpm , volts = 400 , phases = 3, hertz = 50 , full load amps 5.5 Amps,,,, for new pump motor is 1.7KW (1700 watts), full load amps = 5.2 Amps , speed volts phases hertz are the same, this data is from both pumps data sheets.

@Littleinch : the pumped fluid is the same since the old pump as this is an existing unit, however we are currently running the glycol @ 20 C instead of 200 C, although its a huge difference in temperature the impact on density is minimal when checking by pressure = density x G x head and applying on pump curve (testing result curve & rated curve which I uploaded earlier) you are not going to go higher than 5.2 Amps anyways, and so did the old pump.

We do not have any flow device at this line, there is one orifice further but not sure about it if its restriction orifice or delta P for flow testing.

when we ran the pump, pump is quite, no any visible abnormality, and dismateling the pump is not an option its a new item and we have procedures over here, I am trying to get help as the vendor is faaaar away.

efficiency of old pump is 34% and 41% for the new pump ...

RE: high Amps on newly replaced pump

What is the viscosity difference if any between 20c and 200c?

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: high Amps on newly replaced pump

somacast,

Thanks for info

1) Your motor details don't make sense I'm afraid. 5.2 A only makes sense when looking at a single phase motor when power = V X amps ( and that's electric power, not shaft power). Are you sure it's a 3 phase motor?? Looks to me like someone is giving your single phase motor two phases from a 3 phase supply.
2) Even allowing for that, the new motor is less efficient. Old motor 400W/Amp, New motor 325 W/amp
3) I still think you're actually operating on the RHS of your curves. Because the old pump head dropped off quite rapidly this limited the max flow and max power. New pump head curve is longer and flatter so can flow more at a higher head hence more power. Allied to less efficient motor = more amps. Pump is quite happy because it's still operating inside its head curve, but motor is undersized.

You need to be able to measure flow to sort this out. Either that or somehow throttle a valve somewhere in the line to bring the power / current down.

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

RE: high Amps on newly replaced pump

I'd be very surprised if this was a single phase motor

RE: high Amps on newly replaced pump

Regarding: however its drawing 6 Amps of current instead of its stated in datasheet of full load of 5.2 Amps

The nameplate current may be different than the actual full-load current and should not be considered an accurate indication of motor load. Nameplate full-load current value applies only at the rated motor voltage. The root mean square current measurements should always be corrected for voltage.

Did you measure the amps on the old motor?

RE: high Amps on newly replaced pump

If you look at the equation, if your voltage is low, to get the same watts the amps have to be higher.

Again you should do a shut in head test to see if your impellor has been overcut

RE: high Amps on newly replaced pump

"I'd be very surprised if this was a single phase motor"

Why - its 1.7kW. My circular saw motor draws more power than that and it's single phase 240V.

I agree 400V sounds like 3 phase, but then the amps don't work so something isn't correct in the description. a picture of the name plate would probably solve a lot if wheel spinning....

With no flow measurement I don't think we'll ever know, but the pump is doing what it is supposed to do. The issue is with a system which allows more flow and an inefficient motor compared to what has gone before.

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

RE: high Amps on newly replaced pump

I doubt it is single phase. Single phase is a two wire system + ground. A three phase system can be a 3 wire system + ground (sometimes it can be 4 wires, where the 4th wire is the neutral). It would be kind of tough for an electrician to screw this up.

"With no flow measurement I don't think we'll ever know, but the pump is doing what it is supposed to do. The issue is with a system which allows more flow and an inefficient motor compared to what has gone before."


I think doing a simple shut in head test will help in determining if the pump curve that has been supplied is as what is shown. If the impeller is overcut then this will explain the increase in power consumption. BUT you have to reconcile the reported elecrical numbers by supplyimg the information everyone has asked for. Everything is so fuzzy right now

RE: high Amps on newly replaced pump

(OP)
At first I would like to really express my deepest gratitude to all of you, your efforts are really appreciated, thank you all .

and good news is that I finally got it, OPS people insisted on testing it with cold glycol @ 20 , while I had density effect on head checked and checked with pump curve and found it minimal I did miss the viscosity effect, it might sound stupid from me but believe it or not I had many senior people with me and non even though about it, and not even the vendor helpdesk !!, visc @ 205 C is about 39 Cp while at 20 its about 0.8 Cp !!! that's a HUGE difference.

and when I came back to office and topic here it seems like Artisi had it right :) :)

the motor is now drawing about 5 Amps, and regarding the discussion above , its really 3 phase @Littleinch , but as you said its low HP pumps, but special type (canned motor), old pump used to draw about 5.2 Amps when operated too @ 205 C ..

Thank you all really

RE: high Amps on newly replaced pump

QualityTime,

"Remember that for a 3 phase motor POWER (WATTS)= 1.73 * VOLTS * AMPS"

That calculation gives you the apparent power delivered to the motor.

You also need to know the power factor to calculate the active power input from the apparent power, and you additionally need to know the motor efficiency if you want to calculate the power output rather than input. IEC motors are rated based on output power at the shaft, so the relationship between voltage, current and power is a little more complicated than you wrote.

RE: high Amps on newly replaced pump

At 5 amps though it still means you're operating at a different duty point - 5A is very close to your max rated current and shaft power (1.78kW) compared to what the pump should need at your duty point (1.34kW).

Hence I suspect you're still pumping more like 9 m3/hr instead of 6.8...

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

RE: high Amps on newly replaced pump

(OP)
@Littleinch , noted thank you, however there was a big debate on this regard with the vendor when they supplied the pump as their acceptance criteria is just the current, anyway I expect to go to the optimum point when the boiler goes on full duty as our test might have just heated the gycol to a point near 190 C or so , hence there is a chance for improvement when the boiler is on normal operation .

RE: high Amps on newly replaced pump

I'm surprised they accepted that as the power consumption is dependent on the system curve, flowrate, density and viscosity, all of which is outside their control.

You also need to ask them for the phase current next time - I still don't know what the amps you quote relate to...

See if you can get a clamp on flow meter or some other way of working out what the flow is.

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

RE: high Amps on newly replaced pump

If the pump is now operating under the max setting for overload and the system is delivering somewhere near to what is required and management and operator's are happy - why worry about splitting hairs - sign it off as successful and go tackle the next problem.

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: high Amps on newly replaced pump

Because it's still pretty close to the limit and who knows whether some aspect of the plant is working incorrectly because they think 6.8 m3/hr is coming at them instead of 9 or more??

As I know you are aware, far too many people think of centrifugal units as simply "blocks" of flow - "I've bought a pump that says it does 6.8m3/hr so why is it doing 5 or 9? The pump is at fault". I would say 90% of posts that appear here saying the pump isn't working properly turn out to be a system or motor issue instead. If you don't match the pump to the system or provide some sort of flow control or measurement, it won't do what you think it's going to do.

Anyway somacast has the information so he can do what he likes.

It looks like the old pump was operating well beyond its duty point if it was also operating at 5 Amps so maybe that's actually what everyone wants....

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

RE: high Amps on newly replaced pump

LittleInch: after a few years in the pump game, I would say that it is more like 99% of "the pump isn't working properly" isn't the pump - but poor selection, installation, system, or not knowing what the hell they are doing. Some of the stories I could relate are unbelievable - wrong direction, closed valves / blank flanges, no coupling between pump / motor, inlet pipework connected to outlet flange, no product available, no power connected / wrong connections - this isn't even talking about completely wrong selection / specification, or wrong pump for the application etc.

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: high Amps on newly replaced pump

(OP)
Thanks again Artisi & Littleinch , in fact there is a pressure there is a pressure control valve on the discharge, but it was fully open at testing, and over here not really many helpful seniors, I mean I was in this trying to figure it out as it might have caused loss production but thanks God it was solved eventually, but now they are about to do a stupid thing, but it wont be my under my scope as Artisi said, that's it sign it completed..

they are about to about to raise the set current of tripping in the power breaker, justification is : when station is cold started current will jump high... ok go ahead, I am not the one to pay for repairs when the motor is roasted :)

thnx again :)

RE: high Amps on newly replaced pump

Why not start against a restricted discharge until product gets up in temp. and viscosity lowers - this will reduce running current and motor overload.

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: high Amps on newly replaced pump

(OP)
artisi : the problem with operation people is that they are stubborn, so it is not easy to suggest a change in a written procedure, and likely they will go ahead with current set point variation.

Thanks again :)

RE: high Amps on newly replaced pump

Well that's a management problem and it's managements problem to address it. Make your point clear in a written report on the problems of start-up with a cold products and set out the consequences and recommendations to overcome failure - this covers your arse.

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: high Amps on newly replaced pump

(OP)
Thanks I will keep it in mind :)

RE: high Amps on newly replaced pump

Have you taken into account Eddy Current losses through a canned motor ? With seal less pumps you loose quite a lot through this (passing magnetic fields through the shroud/isolation shell) I read that the motor power is 2.2kw - if you were to look at a similar magnetic drive pump that we manufacture, the eddy current losses on this size of coupling are 0.31kw so the pump will pull more power and will result in high current drawing...

The manufacturer will be able to tell you the eddy currentl losses specific to the pump you have purchased.

Ash Fenn

www.cdrpumps.co.uk

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