Dab centrifugal pump

[greenfingersjim]

I have a dab centrifugal pump for pumping water from a holding tank to water plants on a nursery. It’s quite old but generally works well. Recently it’s been cutting out after an hour or so of use. The supply is fine and the motor spins freely when this happens so not seized. 10 mins later it runs again, but only for a while and I have to wait a while again. Is this likely to be overheat protection? Not sure if it even has this feature. Any other ideas as to what might be causing this?

 

[ericmark]

Need more of a clue these are all DAB centrifugal pumps, and are very different to each other.

 

[greenfingersjim]

This one

 

[Harry Bloomfield]

10 mins later it runs again, but only for a while and I have to wait a while again. Is this likely to be overheat protection? Not sure if it even has this feature. Any other ideas as to what might be causing this?

Ask the manufacturer, stating the model details, if it includes overheat protection.

Does restart by itself, if simply left on for those 10 minutes? Does the motor case feel hot?

 

[greenfingersjim]

I’ll probably get someone to look at it but just thought I’d research a little. The current models do have heat protection. This one’s at least 20 years old. It does get hot to touch but don’t know how this compares to before problem started. I wonder if the bearings are dry.

 

[Jurassicspark]

It’s quite old but generally works well. Recently it’s been cutting out after an hour or so of use.

Something is not right. As you would know.

The supply is fine

How do you know? If there is any voltage fluctuations or excessive voltage drop it will draw more current and cut out.

and the motor spins freely when this happens so not seized. 10 mins later it runs again, but only for a while and I have to wait a while again. Is this likely to be overheat protection?

Most likely yes. However, there is a very very little chance it could be a loose wire where the windings connect to.

Not sure if it even has this feature. Any other ideas as to what might be causing this?

Have you got a clamp meter?
Is the motor housing clogged with debris?

 

[Harry Bloomfield]

This one’s at least 20 years old. It does get hot to touch but don’t know how this compares to before problem started. I wonder if the bearings are dry.

Take the fan cover off, and try rotating the fan by hand - that will give you an idea of what the bearing are like. Hot to touch might suggest shorted turns in the motor, but is that just a start capacitor, or is it a dual - start, plus run?

 

[greenfingersjim]

No clamp meter. I haven’t looked inside the motor, but doubt there’s anthong inside as it’s sealed. It is noisier than I remember in the past which makes me wonder about bearings. I have checked the fan and the shaft isn’t loose at all. I had considered the windings. I’m not certain, but I don’t think it’s as powerful as it was, but that could be related to the actual pump. I assume an issue with that could also cause the motor to generate extra heat.

 

[ericmark]

I would guess bearing failure, and the rotor is touching the stator. But that is just a guess, and without some testing hard to tell.

 

[Harry Bloomfield]

I have checked the fan and the shaft isn’t loose at all.

I meant - if the fan + motor shaft are tight to turn, that would suggest a bearing problem. The bottom bearing being the most likely problem, where the water is. It would be worth stripping down, to check the pump isn't choked, and the bottom bearing.

 

[greenfingersjim]

The fan turns freely when it suddenly stops. The electric doesn’t trip, although it did an earlier in the year before this issue arose. I think I’ll get the motor off and have a look and take it to be tested if nothing obvious.

 

[just pumps]

You have an old multi-stage pump there, can`t remember if it has overheat protection or not. There are plain bearings within the pump and ball bearings in the motor. Personally, being an old unit I wouldn`t waste money on having it tested or a rebuild.

 

[morqthana]

Personally, being old I wouldn`t waste money on testing or a rebuild.

Maybe greenfingersjim is younger than you?

 

[greenfingersjim]

I assume the round black component is the thermal overload

 

[Harry Bloomfield]

I assume the round black component is the thermal overload

Probably, but a search for mrh20rx finds nothing. A couple of tests would confirm it - the resistance between those two terminals at the top, will be zero, and - when running, and it stops due to overheating, the resistance will go high.

However, if the motor is getting too hot, then that component is doing what it is there for - switching the motor off.