strange 240v pump 'switching'

I have a submerged fountain pump/motor unit that I clean and remove each winter and reinstall in the spring. The unit is now 10 years old and this year when switched on has developed a repeating pattern of switching off after about 1.5 mins then switching on for the same period, this is repeated until I switch off.

The supply trips are uneffected, I have renewed the 3 pin supply plug and fuse and the unit is submerged in clean water for the whole time. It is probably due for replacement but I am puzzled about what is causing the unit to shut down and start again in a repeating pattern - any ideas?

Tony

You can usually strip the pump down to it's bare components, which i have to do on a regular basis on the pond pumps i have. The usual culprit is crappy stuff getting behind the bushes & causing it to seize.

Steve.

Just think of it as a feature...

Tony

Could it be an internal overload trip (possibly a temperature sensor on the motor) that is operating then resetting?

You don’t say if it is pumping water, but there may be a blockage.

Stuart

Edited By Stuart Smith 5 on 04/04/2021 12:09:14

It sounds like there is some corrosion or resistance to spinning and that is causing a thermal switch in the motor body to cut out. Look at the spindles and bearings and for any foreign body's behind the pump blades etc. As it cools down the motor will start again till it overheats and trip out etc.

David

I think Stuart Smith is probably thinking along the right lines. A thermal cut out (Or an intermittent connection inside the pump.) seems likely. It probably warms up and the contact breaks. It then cools down and the contact re makes.
It would be interesting to monitor the current to the pump to see if the current drops to zero when it stops.
I think a new pump will be the only solution as the ones I have seen are encapsulated in resin.

Les.

Edited By Les Jones 1 on 04/04/2021 12:36:34

I also have one of these submerged pumps and from time to time it stops running, but without restarting. I traced that fault to a badly worn shaft the ferrite impellor runs upon, it was actually grabbing the sides of the tunnel it runs in.

It is now on it's third such shaft, stainless steel versions last about 3 years and eventually wear paper thin at one end. We think it is frog poo in the little pond it lives in that does the damage.

Perhaps Tony's pump is showing early signs of the same malaise.

Brian

Almost certainly the pump is overhating causing a thermal trip to cycle and previously stated by Stuart and David. If it's 10 years old just buy a new one.

Robert G8RPI.

Thanks Guys - I was trying to find a reason for not dismantling the fountain and getting the pump unit out.

It is installed in a sump below a large stainless steel sump fabrication that supports my collection of geological specimens (which weigh a lot) that the water of the fountain sprays over.

I will strip the whole thing down but after 10 years it may be due for replacement

Happy Easter to all

Tony

Is enough water reaching the pump to prevent it running dry and overheating / seizing? I E is the stainless meshh and the stuff on it preventing sufficient flow to the pump?

Howard