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question about small submersible pump bhp vs current characteristics
5

question about small submersible pump bhp vs current characteristics

question about small submersible pump bhp vs current characteristics

(OP)
I have a question about Goulds WE0511HH pumps that we use in a sump application: Submersible Pump. 1/2 HP, 115 Volt, 60 Hz, 3.87″ Impeller, 2″ NPT Discharge, 20′ Cord, 3/4″ Solids.

I'm not sure where is the best place to find info on this pump (google floods me with distributors), but here is a link

Question 1: what does the bhp vs flow curve look like? Does bhp increase with flow, or decrease with flow, or increase then decrease with a peak near bep in the middle?

Question 2 (if question 1 is unknown / ambiguous): what is the construction of the pump (axial flow, radial flow, number of stages)?
I think it's radial flow single stage. I’m under the impression single stage radial flow pumps generally have increasing bhp vs flow while single stage axial flow pumps generally have decreasing bhp vs flow.

Background: We have some chronic problems with this pump tripping, often on start, sometimes during run. Historically we have focused a lot on filtering the suction and blamed the trips on debris. We just noticed we have Bussman KTK-15 fast act fuse which we’ll be upgrading to KTK-20 in hopes to solve the problem. Beyond that we’d still like to understand what role is the system operating point (flow resistance) and also the impact of debris that might end up obstructing flow (we immediately neck the 2” discharge of the pump down to ¾” pipe). Obviously if debris jams the pump that would cause trip but I'm just interested in the effect of the operating point on the current. There are other people here involved reviewing other aspectsm but my piece is just the question about effects of operating point effects on current.


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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

It's a cast iron semi open single impellor so power usually rises with flow, but the goulds manual doesn't give a lot away as the head falls a lot with increase in flow.

Obstructing flow shouldn't cause an overload unless it jams the impellor and you get locked rotor.

The HH bit at the end is High Head and a sample look at some flow number for me says 1/2 hp motor is right on the limit or actually over.

see https://d1pkofokfruj4.cloudfront.net/media/upload/...

The line for the WE0511HH at 115 V states max amps 14.5, locked rotor 46A and max efficiency only 54%.

SO if you're at lower flows, the at say 5m3/hr, its putting out 15m head. Assuming a pump effiency of 0.5 gives me a shaft power of 406W, so 0.53 hp.

The power figures for the two pumps, HH and H are the same which is difficult to believe.

But it could well be that if in fact you're running too fast (can you measure your flow??) then you might be drawing more power than the motor can supply

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

RE: question about small submersible pump bhp vs current characteristics

(OP)
Outstanding, that gives me something I can sink my teeth into. But as always a lot more questions.

> The power figures for the two pumps, HH and H are the same which is difficult to believe

Yeah I'd agree there. 3.56 impeller size for the H version and 3.87″ impeller size for the HH version. My first thought was maybe they were looking at an operating point where the two curves crossed on the figure which looks to be 55 feet and 67gpm from the curve on page 2. But then I scroll to page 4 the table labeled "Performance Ratings" and 55ft is beyond the row where they stop tabulating numbers (beyond shutoff?). They don't tabulate anythign beyond 25ft for the WE05H or 45 ft for WE05HH. It makes no sense to me. Maybe I have mixed my units or something....am I missing something there? I don't understand the relationship of the model numbers on page 4 performance table (example WE05HH) to those on page 2 (example WE0511HH) (I had my part numbers all crossed, sorry).


> But it could well be that if in fact you're running too fast (can you measure your flow??) then you might be drawing more power than the motor can supply

I don't have the nameplate but the motor comes with the pump and the catalog suggests 2-pole motor. We don't have any vfd. I'm not sure how we would be running it too fast.

Another random question, does anyone have any example pump with similar construction from which we might estimate the shape of the efficiency vs bhp flow curve for this pump?


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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

Sorry, when I said too fast, I meant too high a flow rate / end of curve. That eats power.

Or what is your operating head / lift / pressure?

Also can you measure the voltage being supplied when it's running? At 115V, if it is actually say 105V when operating you're going to eat amps

For these sorts of small basic semi open impellor pumps you could be way out as fixed issues will be more than the variable ones.

But basically the mfrs skimp on everything to get a pump which sells more than the next one so I think you're just too close to the wire.

BUY A BIGGER MOTOR

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

RE: question about small submersible pump bhp vs current characteristics

(OP)
Since you mentioned replacing the motor, I looked at the literature data again and I am trying to make sense of this: Max amps is listed as 14.5 for a 0.5hp 115 volt motor.

14.5A at 115 volts is 1667 VA
0.5hp is 0.5*745watts is 272 watts.
If that 14.5A corresponded to nameplate hp the product of pump efficiency times motor efficiency times power factor would have to be:
272/1667 = 0.16

Something seems out of whack to me there. Either the pump is ridiculously inefficient (much lower than that 54% stated) or else the motor is going to run way over nameplate horsepower. Is that the way you're looking at it? I guess the motor efficiency and power factor must be pretty low too.

UPDATE – After upsizing the fuse, we started the pump.
It ran for 15 seconds near locked rotor current (40A), then the internal overload tripped.
Then after 20 more seconds the internal overload reset and motor restarted. This time the current dropped faster.. it got to 20A within a few seconds and then 13A within a few minutes.
(Current traces from the above are shown on slides 1 and 2 attached)

We manually stopped the pump and later restarted it. On this start (2nd manual start, 3rd overall start) the current dropped to 13A within a few seconds (slide 3 attached).

Each of these three successive starts seems to be getting quicker as load presented by the pump is decreasing. In addition during the first start there were erratic current spikes. I’m thinking that might represent some kind of debris in the pump which worked it’s way out as these starts progressed.

There certainly may be some motor upsizing in the works but at the moment our focus is understanding what’s going on and short term actions. Considering asking them to inspect the pump for debris.

questions - have you ever seen a current waveform like that first start? do you think it represents foreign material or something else?

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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

Pete; Those times are completely out of reason. There is something mechanically wrong OR I'm thinking it's a wiring failure. You have a bad joint somewhere. The motor could be single-phasing intermittently or since it's a pump, actually managing to start eventually and run and not go up in smoke as fast as motors not sitting in 'coolant'.

I'd first check the voltage at the absolute closest you can get to motor.

If it's a single phase motor (and looking back at your OP it probably is) then you have a starting capacitor circuit issue. Either it's failed (likely) or the circuit's switch-in/out wiring is bad.

Keith Cress
kcress - http://www.flaminsystems.com

RE: question about small submersible pump bhp vs current characteristics

(OP)
Thanks for your comments Keith.

No doubt the first start was way too slow and the 2nd start (a self-start when I presume the overload reset itself) was somewhat slow compared to the 3rd start. That's why I highlighted those durations.

Yes it is 115vdc

To me an electrical problem does not fit the self-restart. I don't think I explained the scenario well, so let me try to see if I can make it more complete / coherent:

  • t = 0: start the motor (manually). Red light at controller turns on, flow is noted, current goes to 40A.
  • t=0 to t=15 sec - current remains near 40A (with erratic spikes every 0.4-0.8seconds shown on slide 1)
  • t = 15 seconds. Pump stops (by itself). Current goes to 0. Flow stops. Controller red light remains on.
  • t = 15 to t=35 seconds. Current remains 0. Red light remains on.
  • t=35 seconds. Pump starts (by itself). Current goes to 40A. Flow is heard.
  • t=37 seconds. Current is down to 20A.
  • t=1 - 3 minutes - Currents drifts down to 13A.
  • (everything above is on slides 1 and 2).
  • t=10+ minutes. secure the motor (manually).
  • Later on slide 3 motor is restarted (manually), current initially goes to 40 amps and then drops to 14amps in 2 seconds.
I presume the third start (slide 3) is close to what a normal start is. the previous start (self-restart) is abnormal and the first start was very abnormal.

The scenario that makes sense to me is a mechanical problem that slows the motor. The motor internal overload responds as expected by tripping after around 15 seconds of current close to LRC, and then also resets itself as expected 20 seconds later to reenergize the motor. (I'll clarify "as expected" to mean that it sounds reasonable to me, but I need to mention that I don't actually know the characteristics of the motor internal overload for tripping and resetting).

There is also that erratic current after the first start. And the fact that each successive start is a little faster. I postulate maybe these two aspects are explained by some foreign material rattling around in the first start that gradually works its way out. Maybe.

I have a hard time explaining it with an electrical fault of wiring failure or bad joint or cap. It caused the motor circuit to completely open, and then it magically reclosed itself 20 seconds later? Remember also the controller red (running) light stayed on throughout. Does that electrical scenario still seem reasonable to you? It wouldn't be hard to check voltage and poke around the control circuit, but in this particular situation I feel some burden to explain a plausible scenario for whatever I ask them to check.


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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

A few errors creeping in?

The OP says 115V 60Htz, but then in the post above 115vdc??

Typo in 0.5 hp is 372W, not 272.

But the elephant here is 13A running current. That's pretty close to 1.5kW or 2hp WHAT!!

That's more like what the max start current should be for 5 to 10 seconds, not your steady current.

Think you need to take the pump apart. I suspect something is wrapped around the impellor.

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

RE: question about small submersible pump bhp vs current characteristics

(OP)
Yes 115ac.

> But the elephant here is 13A running current. That's pretty close to 1.5kW or 2hp WHAT!!

I think it's clear the pump allows an overload within its operating range as you reasoned before. Slide 3 shows max bhp 0.3hp. If you apply pump efficiency to that you get 0.6hp required on input to the pump. That exceeds motor output 0.5hp rating.

On the motor input side, 13A is within the range of what the literature stated 14.5A and it drew my suspicion as way out of whack in the comments before, but I crossed that out because motor pf and eff are unknown. Let's redo the calc of how that stated current and how it relates to 0.5hp

14.5A at 115 volts is 1667 VA
0.5hp is 0.5*745watts is 372 watts.
If that 14.5A corresponded to nameplate hp the product of pump efficiency times motor efficiency times power factor would have to be:
372/1667 = 0.22

If we chalk up 0.5 of that to the pump, then the product of motor eff and pf would have to be 0.44. That's pretty darned low, but it's a small motor and sometimes they are low (maybe it's something like 0.65 eff and 0.7 pf which would be in the ballpark?). Or maybe they're a bit higher and that 14.5A corresponds to 0.6hp? I don't have any data on motor eff and pf for this 0.5hp motor. I agree there's not a lot of margin there just based on the bhp curve. We've had a lot of trips in the past but no motor damage. Now we've upsized our fuse, we may expose the motor to more abuse. As a long term solution maybe we should be looking at new pump/motor (they come as a combo unit). I think if we observe additional overload trips and that first overload trip was not an anomaly, that will definitely push us there. From the oddball starting pattern (erratic current within the first start with spikes spaced at 0.4-0.8 seconds) I think maybe that first start was something atypical.

=====================================
(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

I would still take the casing off and see if there's something wrapped around the shaft.

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

RE: question about small submersible pump bhp vs current characteristics

(OP)
Thanks LI. I'll recommend that.

Quote (electricpete)

I think it's clear the pump allows an overload within its operating range as you reasoned before. Slide 3 shows max bhp 0.3hp. If you apply pump efficiency to that you get 0.6hp required on input to the pump. That exceeds motor output 0.5hp rating.
That was a little sloppy iwith everything rounded to one sig figure. Just to try it with two sig figures.

Quote (electricpete 2 sig figures)

Slide 3 shows max bhp 0.31 hp. If you apply stated pump efficiency 0.54 to that you get 0.56hp required on input to the pump. That exceeds motor output 0.5hp rating.

I realize these numbers are not all that exact to begin with (and I don't even know which operating point that 0.54 pump efficiency number applies to) but I want to carry around these particular numbers in my head for a few days and correcting it here in this thread makes that easier for me.

=====================================
(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

(OP)
Attached is an update to my previous slides to clean them up a little bit and describe those three starts from yesterday 5/18 more clearly:
  • • First start was a normal manual start, second was a self restart when the internal overload cleared, third was a normal manual start.
  • • The first start was abnormal with current hovering near locked rotor current 40A for 15 seconds before tripping on internal overload. There were also some unusual current spikes in this time period shown on slide 1.
  • • The third start (slide 3) appeared to be a normal start with current dropping to 14amps within 2 seconds and 13 amps within a few more seconds.
  • • The second was somewhere in between (details on slide 2) with current dropping to 20Arms in 2 seconds, then slowly decreased to 13A over a few minutes.
  • • With the starts getting successively quicker and the erratic current in the first slide, it suggests maybe there was foreign material stuck during the first start that eventually moved out of the way somehow.
Slides 4 through 6 summarize the pump performance and the lack of margin for this motor in the middle of the range (even without debris problems). With increased fuse setting no doubt we may decrease tripping problems but we may see more motor failures (remains to be seen). If overload is prone to tripping and resetting without any operator action, we might not notice those occurences until a motor failure and fuse blown.

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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

(OP)
What does the symbol below mean? (this was on the pump curve):



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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

Yeh, I saw that and wondered the same thing....

Duhhh Just figured it out - It's just telling you what each little box on the pump curve is....

It's not a standard format of pump curve. It doesn't have efficiency and it doesn't have power., but then it is trying to show a lot of small pumps on one graph instead of one each.





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

RE: question about small submersible pump bhp vs current characteristics

(OP)
Ha! That's funny. That's pretty obvious in retrospect, although still kind of odd (they would have been better of just omitting that imo).
Thanks for figuring it out, and also for making me feel better in not being the only one confused by that!

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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

These small pumps are known to be very sloppy. The performance is all over the place.
We used to build large subs, but had a bunch of small ones like this for emptying pits and such.
We figured that 1 out of 4 would be trash when new.
25% differences in power or performance didn't surprise us.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: question about small submersible pump bhp vs current characteristics

Centrifugal pumps draw more current with higher flows. What you observe may simply be caused by having a very long discharge pipe the takes a long time to fill.

RE: question about small submersible pump bhp vs current characteristics

Yes, 1/2 hp is barely like powering this with a drill.

If you still get trouble then try throttling the discharge a bit to reduce power. After you've cleaned it.

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

RE: question about small submersible pump bhp vs current characteristics

(OP)
At one time I posted a motors forum FAQ with my simple understanding of BHP vs flow behavior for various "centrifugal" pumps: FAQ237-1543: How does hp change with flow for a "centrifugal pump".


I did compute the FHP vs flow curve in my attachment. That particular curve is highest in the middle of the operating flow range and lower on each end. Of course we'd rather know BHP vs flow (rather than FHP vs flow) but I don't have that. My best guess is the qualitative behavior of that BHP curve would be the same (highest in the middle of the operating range. I'm curious if anyone agrees/disagrees with that.

If that is correct, it would match the shape I associate with "mixed flow" pumps. I don't know what is the actual classification of this pump in terms of flow direction, I'd also welcome if anyone can tell me that.



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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

In a radial flow pump, the liquid enters at the center of the impeller and is directed out along the impeller blades in a direction at right angles to the pump shaft. This type of pump pump combines the hydraulic design of an end-suction pump with a submersible motor. Submersible pumps are always of the close-coupled type – meaning that the overhung vortex impeller mounts directly on the end of the motor shaft, and the pump casing attaches directly to the motor frame.

1/2 HP is 373 watts. These effluent sump pumps have low efficiencies and probably operate at 35 - 40% efficiencies, then your continuous watts could be as high as 373/0.35 = 1070 watts. But they say the startup draw can be 1.5x-2x the continuous draw, so you might consume up to 2100+ watts. That’s roughly as high as 18.3 Amps.

RE: question about small submersible pump bhp vs current characteristics

The missing info in your calculation is efficiency. Tends to be low at low and big flows so power tends to steadily climb as flow increases or doesn't drop off.

Do you actually know what the normal running flow rate is?

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

RE: question about small submersible pump bhp vs current characteristics

One thing to consider is that submersible pumps motors are usually rated to run at higher current for their rated output due to being product cooled, unlike a none submerged motor running in air.

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: question about small submersible pump bhp vs current characteristics

(OP)
bimr - so would you classify it as radial flow, axial flow, or mixed?

LittleInch - Yes, I have one value of pump efficiency but no curve, so limited ability to forecast the shape of BHP curve from FHP curve. I think you're saying that if pump efficiency curve was taken into account, it would be a monotonically increasing curve of BHP vs flow? What makes you say that?

We don't have a flow indicator, but I'll check around to see if there is a way to begin to estimate actual flow rate in our system. As I mentioned we have an immediate neckdown in piping from the 2" discharge pipe to a 3/4" pipe which looks very odd, but I don't know how long that 3/4" pipe runs for.

Artisi - I have seen some motors (noteably TEAO) where the hp rating of the motor takes credit for the favorable environmental conditions (flow over the motor in the case of TEAO, plays a similar role as submergence I would think) and is stated as such on the nameplate. I don't have any nameplate photo for this motor, so at first glance I'm leery of taking credit for some rating beyond 0.5hp (although as Ed points out probably none of this is very exact anyway)







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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics


Quote (electricpete)

bimr - so would you classify it as radial flow, axial flow, or mixed?

No, not a radial flow pump. In a radial flow pump, the liquid enters at the center of the impeller and is directed out along the impeller blades in a direction at right angles to the pump shaft.



No, not an axial flow pump. Axial flow pumps are of the propeller type, in which the rotation of the impeller forces the water forward axially, and do not strictly qualify as centrifugal pumps. Mixed flow pumps act partly by centrifugal action and partly by propeller action, the blades of the impeller being given some degree of ‘twist’.



No, not a mixed flow pump. A mixed flow pump is a centrifugal pump with a mixed flow impeller.



The submersible pump you are referencing is called a vortex pump.



Submersible Vortex Pump

Goulds Vortex Pump

RE: question about small submersible pump bhp vs current characteristics

While I kinda concur with something wrapped around the shaft OR the bearings have failed think about this:
If the start cap is bad it would act exactly the same as you're seeing. It would have a hard time starting and suck-down LRA until it managed to trip the small single phase motor built-in overload. Then try again and maybe manage to get up to a faster speed before tripping-out. Then on a third cycle get running fast enough to run normally as it's now finally actually fully started.

Does it have a start capacitor?

Keith Cress
kcress - http://www.flaminsystems.com

RE: question about small submersible pump bhp vs current characteristics

Quote (itsmoked)

Does it have a start capacitor?

Motor Type: Oil Filled Capacitor Start

Goulds Model No. WE0511H

RE: question about small submersible pump bhp vs current characteristics

(OP)
Thanks that's some great info all around. As luck luck would have it, we have recorded 9 more starts on Thursday 5/19. They were not particularly prudent starts (many quick starts in a row resulting in trips, lots of abuse of that motor) but that's what was done.

I continued the numbering of starts from 1/2/3 on 5/18 to 4 through 12 on 5/19 (the starts numbered 4 thru 12 are shown attached). It is an interesting opportunity to look at these starts some more, even though maybe the resulting troubleshooting actions are already obvious straightforward.

On 5/19 I saw some normal starts similar to the start 3 (example start 4 on slide 2). I saw some struggling starts with oscillation and then trip similar to start 1 (example start 6 on slide 3). Now here are two new types of starts I saw:

Start 12 (slides 13 and 14) - 5 seconds oscillating near locked rotor current. During this 5 sec the spikes get further apart. After 5 seconds the current drops to normal and the motor continues to run. So it struggled and then finally succeeded.

Start 8. Steady locked rotor current for 4.5 seconds (no oscillation), and then trip. The trip after only 4.5 seconds (where other starts lasted 9+ seconds before trip) I attribute to recent previous frequent starts with insufficient rest/cooling between starts...

To me the steady current in start 8 seems more consistent with completeley locked rotor and something like a cap problem. Myself I typically associate motor starting cap problem with complete inability to start where the motor never moves at all (like I think was going on in start 8). Typically on other motors I've seen with starting cap problem if you give it a push to get started, then it continues to start successfully, at least in the motors I have played with. I guess the starting capacitors play different roles in different styles of motors, so maybe starting cap problem could contribute to a weak start rotating start in some of those? I'm not sure. Certainly a voltage problem could cause a weak rotating start.

I wasn't present during all of this. I wish I was. The technicians who did the test said they could in general tell when water was flowing but they weren't really paying attention to whether water was flowing or not during all of these starts. (They never noticed a start with water not flowing but they couldn't guarantee water flowed during all start attempts)

At any rate, I don't rule out we might have multiple problems and one of them could be starting cap or voltage problem, so I definitely have enough ammunition to suggest checking those things (along with inspecting the pump, which hasn't been done yet).

=====================================
(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

I'm amazed at how much time we have taken discussing a 1/2 hp submersible pump....

It's not a vortex pump, but has some strange characteristics - more like an axial pump in that the difference in head from no flow to max flow is about 10:1. This is worse for the High Head HH versions of the pump.

So it makes it difficult to know what the power does as flow changes. It might peak at some point and then reduce or go in a wave form.

But from the last post it looks like this unit doesn't like starting. Why? Could be a motor start issue, could be stuff wrapped around the impellor, could be just a poor construction. It does seem that the starts in some cases jump a bit at a time, but just does't start.

So time to pull the unit and take it apart I think....

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

RE: question about small submersible pump bhp vs current characteristics

(OP)
> I'm amazed at how much time we have taken discussing a 1/2 hp submersible pump....

Haha yes it is quite a bit, isn't it. I can blame part of that on some organizational factors (limited manpower for troubleshooting at the moment, among other things). We also want to make sure we not only fix the problem but understand it well enough to make a dent in what we now perceive as a chronic problem. And the solutions may not be as simple to implement as you'd think: for one thing we have an onerous configuration control process for changes that are not "like-for-like". For another thing, this is actually a sump sample pump which feeds a monitor for certain sump contaminants (I simplified when I initially called it a sump pump). The relevance of that fact is that I am not sure whether changing the flow rate would change the calibration of the monitor (I'll have to look into that further to see how the monitor works).

But I'll have to take some of the blame myself. For one thing I have a wandering personal style where writing everything down helps me to organize my thoughts.... and so why not just write it all down here on the forum!?! (half kidding, but that explains to some extent the wandering thread).

As if that's not bad enough for you readers, I have ended up with multiple purposes in this single thread:
  1. To understand what specifically caused these particular trips
  2. To understand what might lead to trips in the future if we don't change anything beyond swapping out the pump/motor like for like
  3. To understand the original question BHP vs flow. After I made a statement to a manager that the bhp is not necessarily monotonically increasing with flow, he turned around and assigned me an action to figure out what the curve looks like for this particular pump. Being cognizant of technical factors and also political factors, I feel a burden to complete my assigned action the best that I can.
On the last question, here is a cutaway from the manual


I see it looks like the flow enters the bottom and exits purely radially. Is that enough to call it a radial flow pump?

(btw the annotations I put on the cutaway drawing are just to highlight to myself that it's an oil-filled motor and the cap is located inside the oil)

I may try to engage the OEM with some questions at some point if I can find a good person to talk to.

Thanks again for all your help and patience (with my rambling)




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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

I suspect the only way to get a good BHP vs flow is to do aa set of tests yourself.

So /you would need to have a control valve and a flow meter with pressure guage up stream and then screw the valve down closed, get the pump running and then then do a series of increasing flow in say 5 GPM steps and measure the power in.

Yes I think it's a radial type pump, but I suspect with some straight or straight angled blades and as said, the pump curves resemble more of an axial flow pump than a normal centrifugal, but then its a small sump pump.

We don't know what caused the trips and I doubt you'll ever find out unless you either replace the capacitor or take the pump apart and confirm or deny that there's some sh1t stuck in it. These things are as simple as you can get. If the motor doesn't start, 1st point of call is to check the motor. There should be enough torque to get the pump moving unless you've got a rock stuck in it or something else is clogging the impellor or shaft.

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

RE: question about small submersible pump bhp vs current characteristics

The manufacturers call these submersibles vortex pumps. You can call these pumps anything you want, but if you look at the cross-sections above, you can see that the pump in question is not constructed like a radial pump.

A radial pump has:

1. Flow passing through the middle of the impeller;
2. Has an impeller instead of open ended vanes;
3. Doesn't have a larger open end than a vortex pump;
4. A radial pump is not considered to be non-clogging unless the pump is very large;
5. A radial pump has a higher pumping efficiency than a vortex pump.

An axial pump has a propeller instead of a vane.

The vortex pump is a type of vane pump. In terms of principle and structure, it is different from centrifugal and axial flow pumps. Because it sucks and discharges liquid by the action of swirling liquid generated by impeller's high-speed rotation, it is called a vortex pump. That is why the vortex pump is considered to be non-clogging (or seldom clogging) and also has a lower pumping efficiency.

Link

I do agree with LittleInch that you are spending too much time on this as these pumps are inexpensive and considered to be throw-aways. Many of these sump pumps are configured with cheap level switches that last only 5-7 years. You can get around the level switch issues by hot wiring the pump and using an electronic switch like the levelguard.

RE: question about small submersible pump bhp vs current characteristics

(OP)
Thanks bimr. I can see the idea of vortex pump like in your original figure can move chunky fluid without anything having to go through the impeller, in part I guess due to the open vane design of the impeller and in part due to the fact the impeller is above the elevation of the discharge. Our pump in the figure I excerpted above is slightly different than the one you posted in that our impeller (piece 1) is at the same elevation as the discharge. Does that change your classification at all? (just a curiosity).

> I do agree with LittleInch that you are spending too much time on this as these pumps are inexpensive and considered to be throw-aways

I have addressed some of the challenges described in my last message. (Or you could just say I have some issues...)

I've recommended:
  1. Replace pump/motor. Inspect sump and accessible portions of pump that can be seen through the suction port. Clean sump.
  2. Perform additional monitored starts of replacement pump/motor, this time monitoring voltage near motor along with current (and give it some rest between starts).
  3. For removed pump/motor, hold onto it and we'll review how difficult it would be to disassemble that oil-filled unit for further checks of impeller and capacitor.
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RE: question about small submersible pump bhp vs current characteristics

Have you been able to get in touch with Goulds to get an engineering submittal or anything on this pump? When I deal with them on a project I usually get a lot more documentation than is available on the website or third party downloads. I'd hate to see you spend a good deal more time chasing down the BHP curve through testing only to have it readily available from the manufacturer.

RE: question about small submersible pump bhp vs current characteristics

(OP)
No I haven't tried the OEM yet. Do you have any contacts in mind? Or just start with the main number.

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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

I've got a contact I can chase down that might be able to get back to me within the month. Xylem brands have been having issues even picking up the phone.

RE: question about small submersible pump bhp vs current characteristics

"For removed pump/motor, hold onto it and we'll review how difficult it would be to disassemble that oil-filled unit for further checks of impeller and capacitor."

I'm pretty sure from looking at some manuals and drawings that the inlet plate just unbolts from the rest of the oil filled motor section so that' bit should be easy.

Dismantling the rest looks equally easy to unbolt it, but then you have the rotor and all the insides in a vat of oil.

Rather than all these stop starts to pick up some samples, could you not just keep it running for a set period and route the output back into the tank?

It would be nice to see what sort of impellor or vanes it has and whether there is anything there which is restricting its free movement / increased starting torque. Whatever it has it is pretty basic and needs to just whirl around creating some sort of flow in the liquid.

Let us know how you get on and send some photos of the pump when you've taken the casing off please.

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

RE: question about small submersible pump bhp vs current characteristics

I got a response from my Goulds sales rep with nothing more than the latest revision of the brochure document that was in LI's first post (not even so much as "hello, see attached"). At least it's a newer revision than you had previously.

The state of vendors these days deserves its own lengthy rant post.

RE: question about small submersible pump bhp vs current characteristics

(OP)
Thank Rputvin, that's a few years newer.

As far as the operating point for this motor, we do have a flow indicator in the monitor itself and I'm told the pump typically pumps 5-6gpm (way to the left side of the curve). The monitor calibration is not affected as long as flow remains above 3gpm, at which point we get a low-flow alarm from a flow switch (there is no history of low flow alarms except when the pump has tripped). Being that far left on the curve we have more reason to think that increasing flow would increase current in this region, correct? I don't think decreasing flow will be an option and I don't think increasing flow would help us. If I can figure out a way to increase flow slightly and check current I'll do that.

> Rather than all these stop starts to pick up some samples, could you not just keep it running for a set period and route the output back into the tank?

We mostly operate the pump in manual mode continuous run, so it doesn't see much cycling normally. All the cycles I posted from 5/18 and 5/19 were starts for testing purposes (someone got just a little bit carried away... it wasn't me).

The original design of the monitor provided for automatic cycling of the pump controlled by the monitor (even though it now runs in manual / continually). The motor is switched by a Teledyne 615-6 solid state relay (rated 40A at 60hz) controlled by 24vdc. As an aside the relay has a varistor on it that has an odd bulge in the coating. Even if the varistor is degraded, I don't see any relevance to the motor tripping (if anything it might threaten the electronics). More info attached. Our technicians plan to replace the ssr / varistor out of an abundance of caution when they swap the pump. I don't know much about ssr's... there isn't any degradation mode that would send a low voltage to the motor, is there? (I guess if we had checked voltage before like Keith said, then we'd know that, but as it is we won't get a voltage check until after SSR is replaced).

New pump/motor is in the shop ready for installation, it looks just like the picture in the brochure. I will be able to get a better look at the old one today or tomorrow.

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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

(OP)
UPDATE - pump was removed and inspected.

  1. photos of inspection are here.
  2. The impeller was slightly rough to rotate by hand.
  3. There was no abnormal foreign material, but...
  4. the upper and lower bearings were both degraded (lower bearing has around 0.030” clearance and upper bearing has around 0.020” clearance). The impeller rubbed the bottom of the stationary casing (possibly due to the degraded bearing). The motor rotor may have rubbed the stator.
  5. The friction associated with these conditions may have been the cause of the erratic pump performance.
  6. The pump/motor had been installed since January 2022
  7. The drained fluid was only oil, there did not appear to be any water mixed in
This pump/motor had last been replaced 5 months ago (it was new at that time). It's strange that both bearings degraded. Do you guys think the operating point (6gpm far on the left of the curve) may play a role?

I might have the bearings cut apart for further inspection. Also might try to check the mechanical balance of that impeller.


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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

That is an odd pump. There is only one impeller vane. It looks like it is not even balanced.

RE: question about small submersible pump bhp vs current characteristics

(OP)
Here is another view of the impeller. It rotates at 3500rpm. I'm sure others could explain better than me why it's shaped that way. There is a dead / void space which I think is supposed to help maintain balance (it would be further out of balance if the void space was filled). But gunk accumulates in the void space.

Now that you mention it, I guess this design would cause a hydraulic unbalance force too, but I have no idea how much.






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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

(OP)
I guess I should have mentioned there were metal shavings clinging to the upper bearing as if it was magnetized (slide 8). I can't explain it, so I tend to discount it as irrelevant, but you never know...


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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

Thanks for the update.

I would bet the farm that the impeller has been balanced.

RE: question about small submersible pump bhp vs current characteristics

(OP)
Yes you're probably right that attention was given to mechanical balance in the geometry of that impeller (I think it's cast). I'm not sure if the OEM went the extra step to do a rotating balance check. Thinking about that gunk some more, it's probably roughly the same density as the water it displaces, so maybe not much effect on mechanical unbalance. At any rate, we will be able to check and quantify the mechanical unbalance by putting the rotor and impeller on a balance stand.

But the fluid unbalance (based on lack of angular symmetry of the pumping action) is a different matter. What do you guys think about that... could that be a significant force?

I'm just trying to think of things that may have affected both bearings in such a short time (5 months since install)

Next steps will include inspection of the bearings after they are cut apart (to see if they held onto any clues about their killer!).

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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

Nothing unusual with the impeller, it's simply a single channel design, and would be balanced during its manufacture.

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: question about small submersible pump bhp vs current characteristics

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: question about small submersible pump bhp vs current characteristics

I think the issue is what effect that layer of compressed dirt in the hole part had on the balance of the impellor. The dirt you can see in the photo two above I think would be enough to unbalance it and create vibrations sufficient to damage the bearings.

Leaving a hole like that in a dirty water pump doesn't look like a great idea to me.

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

RE: question about small submersible pump bhp vs current characteristics

(OP)
Thanks. I appreciate your inputs. From a practical standpoint, I'd probably do best to wait to cut apart the bearings (they may render this discussion moot). But I enjoy the discussion and it's a learning experience for me to formulate my thoughts and bounce them off of you guys (especially if you can correct any misconceptions that I have).

Regarding mechanical unbalance, my first thought was build up of gunk would be a problem. My second thought was maybe not because the density is probably not much different than the water it displaces. Now my third thought: how do I know that chamber will be filled with water instead of air. I don't think there is an escape vent on the top. What prevents a bubble of air from remaining trapped in that chamber indefinitely? In that case the gunk is again important because it's displacing air instead of water.


Some unimportant rambling:
So to put it in perspective, what is the unbalance importance of that entire void assuming filled with water:
Below is a rough discussion / calculation that suggests that the difference in unbalance of that void space if filled with something at water density would not be insignificant:
  • SKF lists the "fatigue load limit" of 6203 bearing as 0.2kn ~ 45 lbf.
  • At 3600rpm, 1 inch ounce of unbalance would cause 23 lbf of centrifugal force. (that's my thumbrule to compute F = M*R*W^2, with unit conversions)
  • The radius of the impeller is 3.88" and the height is about 1".
  • Let's say I model that empty space as roughly a 120 degree sector going from redius=1.0" to radius = 1.5" (it's probably bigger than that but I'll estimate on the small side).
  • Then the volume is (1/3)*pi*L*(Ro^2-Ri^2) = pi*1"*(1.5"^2-1"^2)~4/3 in^3.
  • Multiply by density of water ~ 0.58 lbm/inch^3 and it's 2.3/3 ounces difference between full and empty void
  • At an average radius of 1.25" that's about 1 inch ounce unbalance. At 3600 rpm that gives about 23 lbf of centrifugal force.
  • If I applied simplified static analysis to that force (neglecting mass acceleration which might reduce the effects) then the force on the bottom bearing is going to be higher than 23 lbf (in order to satisfy both static equilibrium based on both sum of forces and sum of moments among the two bearings).
  • There are also thrust loads to consider.
  • Considering the above two bullets, it's not hard to imagine these unbalance loads contribute to reaching the fatigue limit of 45 lbf.
  • There's a lot of unknowns and uncertainties (and sloppy calculations * ) in all of that but it gives me the feeling that the difference in forces between a full and empty void are not necessarily insignificant with respect to bearing forces.
  • *If I get a chance I might redo those calculation on some computer-assisted platform to try to make it more reliable and readable and I might tweak the dimensions I chose for Ro and Ri and incorporate the axial distance between bearings along with axial distance to impeller to estimate the two bearing forces which would be necessary to satisfy a postulated static equilibrium of forces and moments)

Setting aside mechanical unbalance, what do you guys think about "hydraulic unbalance"? I think "hydraulic unbalance" refers to a net radial rotating force on the rotor created by the angular distributions of pressures and the flow-related mass accelerations... unrelated to any mechanical unbalance. In a typical impeller, there is a repeating pattern around the impeller itself which tends to creates symmetry... looking at a typical impeller neglecting manufacturing imperfections we'd generally conclude the hydraulic unbalance is zero based on the angular symmetry of the impeller (maybe the asymmetries created by the stationary components would create radial forces on the rotor, but those wouldn't rotate with the impeller so I don't think you call that hydraulic unbalance). But here in this impeller we can see asymmetries in the rotating parts themselves which seem like they would contribute to "hydraulic unbalance". I don't know how big those hydraulic unbalance forces would be.

Less important rambling - I guess I could develop unrealistic far-worst case bounding over-estimates of hydraulic unbalance using very simplistic and conservative assumptions. If those forces come out insignificant even with those overly-conservative bounding assumptions then I know they're not significant. If they seem significant then I'd still not know anything useful because my assumptions are overly conservative:
  • conservatively-high over-estimate of fluid acceleration component of the hydraulic unbalance... something like F = d/dt(m*v) = v * dm/dt where v is a max velocity and dm/dt is mass flowrate (based on the 6 gpm operating point).
  • conservatively-high over-estimate of pressure component of the hydraulic unbalance... F = P*A where P is pump differential pressure and A is cross sectional area (diameter times height) of impeller


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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

(OP)
Two months later, we just got the dissected bearings back from our machine shop (what lightning speed winky smile )

I don't have photos yet but I'm posting here to make sure the thread stays open (I don't know the expiration date of threads).

First impression on inspecting the dissected lower bearing (which was previously noted to have excess clearance while assembled)
  1. * The inner and outer races don't show any obvious distress at first glance other than possible scrape marks on the elevated "lands" on each side of the spherical rolling elements (people tend to giggle when I say balls)
  2. * The rolling elements DO show severe wear with multiple obvious pitting sites on each one.
  3. * I can easily pass the rolling elements back and forth through the cage pocket. I don't think that's normal. These are tiny fabricated cages. I know you can't pass the rolling element through the cage in the fabricated cages of larger bearings, typically when those are dissected they cut the cage into two arcs and the rolling elemetns remain in each half... in this case the rolling elements just fell right out of the intact cage). I haven't looked at many tiny bearings before, but I don't think it's normal for tiny bearings either, is it? If it's abnormal, then I'll take it as an indication that the wear / damage of the rolling elements was severe enough to make them smaller than original.
  4. * The cage has scrapes as if it contacted the inner and outer race lands on each side of the bearing. These are much more obvious than the scrapes on the lands themselves (I think the race is much harder material than the cage).
  5. * There were metallic shavings in the grease, presumably from the cage wear.
  6. * Maybe the decreased diameter of the rolling elements resulted in the cage being less constrained in position, hence it rubbed the land. I can't really imagine the opposite scenario that the cage rubbed in the non-worn condition resulting in debris that created the rolling element wear
  7. * What is the original problem that would have resulted in rolling element wear (assuming that came before cage rubbing land), I have no idea.
  8. * Photos to follow.
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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

(OP)
Repeat of lower bearing findings, with some edits in red. Photos attached.

Quote (electricpete)


  1. * The inner and outer races don't show any obvious distress at first glance other than possible scrape marks on the elevated "lands" on each side of the spherical rolling elements (people tend to giggle when I say balls)
  2. * The rolling elements DO show severe wear with multiple obvious pitting sites on each one. (slide 5)
  3. * I can easily pass the rolling elements back and forth through the cage pocket. I don't think that's normal. These are tiny fabricated cages. I know you can't pass the rolling element through the cage in the fabricated cages of larger bearings, typically when those are dissected they cut the cage into two arcs and the rolling elemetns remain in each half... in this case the rolling elements just fell right out of the intact cage). I haven't looked at many tiny bearings before, but I don't think it's normal for tiny bearings either, is it? If it's abnormal, then I'll take it as an indication that the wear / damage of the rolling elements was severe enough to make them smaller than original.
  4. * The cage has scrapes as if it contacted the inner and outer race lands on each side of the bearing. These are much more obvious than the scrapes on the lands themselves (I think the race is much harder material than the cage). (slides 2, 3, 4)
  5. * There were metallic shavings in the grease, presumably from the cage wear.
  6. * The races were both magnetized

Upper bearing findings:

  1. * The rolling elements have large rough patches. Usually there is a pattern of a large band of rough surface centered on an equatorial line, with smooth circles where the poles would be (slides 7 and 8). Maybe it suggests the rolling element spin axis was not changing, or that sliding was occuring.
  2. * The rolling elements are not as loose in the cage as the lower bearing. We did manage to get one out and used the cage pocket for comparing the size of the rolling elements and the rolling elements from the lower bearing. The rolling elements from the lower bearing could easily go through the cage pocket. This is either due to a smaller diameter or less roughness.
  3. * The wear of the cage against the outer ring does not appear to be as severe as the lower beairng.
  4. * Like the upper bearing, the races were magnetized and metallic shavings were found.
Considering the poor condition of the rolling elements and relatively good condition of the races, it also raises a possible scenario of bad quality bearings. I'm less inclined to think it was operating to the left of the curve that beat up the bearings, but who knows.

What do you think caused the bearing failure?

PS - At this point I post it mostly for a case study. I'm not sure understanding the bearing failure will change any of our actions.

Attachment https://files.engineering.com/getfile.aspx?folder=...

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(2B)+(2B)' ?

RE: question about small submersible pump bhp vs current characteristics

Simple answer to what caused the problem is clearly shown in photo 6/8 - "China"

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: question about small submersible pump bhp vs current characteristics

(OP)
I noticed that too. The brand is NSK. I would say they're more reputable than most Chinese bearing brands (they are certainly more familiar). Then again, counterfeit bearings are a thing.

I've never seen rolling element damage anywhere near this bad without a hint of spalling / damage to either inner or outer race (*). It leads me to wonder if the rolling element material was substandard. Has anyone seen that type of thing before?

(* then again I don't normally look at bearings this small... 6203).

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(2B)+(2B)' ?

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