DC Flexible Impeller Pump Problem

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Dave100456

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Hi
Any suggestions pls re a pump that’s not working. It has worked reliably for a year and nothing has been changed.
It’s a DC Flexible Impeller Pump driven by a 12v motor.

one of these. https://www.spxflow.com/en/johnson-pump-marine/pd-marine-DC-driven-flexible-impeller-pumps/


Turn it on and it self primes taking less than one second or so. Then it pulses for a fraction of a second every two or three seconds.
When the impeller cover plate is removed or the whole pump body is removed the motor will run ok. There’s no mechanical obstruction to the impeller turning.
The electric motor shaft can be turned by hand but is notchy.

Is it a faulty electric motor that isn’t now producing sufficient torque?

Have emailed Johnson Pumps but won’t get an answer until next week. Any advice here appreciated.

Thank you
Dave
 
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Dave100456 said:
Hi
Any suggestions pls re a pump that’s not working. ..............

Turn it on and it self primes taking less than one second or so. Then it pulses for a fraction of a second every two or three seconds.
When the impeller cover plate is removed or the whole pump body is removed the motor will run ok. There’s no mechanical obstruction to the impeller turning.
The electric motor shaft can be turned by hand but is notchy.

Is it a faulty electric motor that isn’t now producing sufficient torque?

Any advice here appreciated.

Thank you
Dave
Click to expand...

IT should turn freely and smoothly,

Bearings or, as pvc suggests, brushes ????

Probably no spares for the motor from Johnson pumps but any bearing stockist shouldbmbe able to supply bearings and an auto electrician may be able to match the brushes
 
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Thanks for suggestions. As the unit is just over a year old I’m reluctant to strip the motor until Johnson confirm if it is or not out of warranty.
Will try next week
 
Dave100456 said:
Thanks for suggestions. As the unit is just over a year old I’m reluctant to strip the motor until Johnson confirm if it is or not out of warranty.
Will try next week
Click to expand...

If it's only a year old it should be in warranty; EU regulations specify a minimum 2 year warranty, I believe.
 
frequently dc motors feel notchy, as there is a permanent magnet. rotating the shaft and it feels as if it jumps, or be stiffer as it passes the poles.

I would look for a leaky non return valve, which is letting the pressure off , along with no expansion vessel, causing the pump to operate in this manner.
 
Dave100456 said:
Hi
Any suggestions pls re a pump that’s not working. It has worked reliably for a year and nothing has been changed.
It’s a DC Flexible Impeller Pump driven by a 12v motor.

one of these. https://www.spxflow.com/en/johnson-pump-marine/pd-marine-DC-driven-flexible-impeller-pumps/


Turn it on and it self primes taking less than one second or so. Then it pulses for a fraction of a second every two or three seconds.
When the impeller cover plate is removed or the whole pump body is removed the motor will run ok. There’s no mechanical obstruction to the impeller turning.
The electric motor shaft can be turned by hand but is notchy.

Is it a faulty electric motor that isn’t now producing sufficient torque?

Have emailed Johnson Pumps but won’t get an answer until next week. Any advice here appreciated.

Thank you
Dave
Click to expand...

What is the pump used for and what else is in the pipe run, such as valves and pressure switches.

Www.solocoastalsailing.co.uk
 
I have a DC gear pump like that. What it is in my case is one of the rotor coils has become open circuit and it the motor stops with the brushed on that coil the motor will not start but if I remove the cover plate and turn the motor shaft a little it will then start and keep running.

It could be when you remove the cover plate then motor is turned away from this OC coil then it will run until it stops of the OC coil again.
 
Roger, I think what you are describing could well be the issue with my pump. There are no other valves in the line and power supply is fine.
I hope Johnson will get in touch with me soon to confirm how the issue can be resolved.
Thank you to other posters offering suggestions.
 
Dave100456 said:
Roger, I think what you are describing could well be the issue with my pump. There are no other valves in the line and power supply is fine.
I hope Johnson will get in touch with me soon to confirm how the issue can be resolved.
Thank you to other posters offering suggestions.
Click to expand...

In your opening pot you said that the electric motor shaft can be turned by hand but is notchy.

I don't think the fault Roger describes will cause this "notchy" feel when turned by hand
 
VicS said:
In your opening pot you said that the electric motor shaft can be turned by hand but is notchy.

I don't think the fault Roger describes will cause this "notchy" feel when turned by hand
Click to expand...

You are correct there Vic but as someone else said the notchy feel could be due to the interaction between the permanent magnet and the rotor metal becoming slightly magnetic.
 
Rogershaw said:
You are correct there Vic but as someone else said the notchy feel could be due to the interaction between the permanent magnet and the rotor metal becoming slightly magnetic.
Click to expand...

+1; notchiness can be inherent in a permanent magnet motor. The strange symptom to my mind is the regular pulsing when the pump is stationary. I'd suspect a problem with the 12v. supply or some control within the supply.
If there's a commutator/rotor problem, the pump would either start or remain dead, which isn't the case here.
 
Runs fine under no load then stops when loaded still sugests power supply to me.
A poor or resistive connection somewhere in the line can break down when asked to carry sufficient current for the motor to do work.
Tried a test lead direct between battery and pump?
 
smb said:
Runs fine under no load then stops when loaded still sugests power supply to me.
A poor or resistive connection somewhere in the line can break down when asked to carry sufficient current for the motor to do work.
Tried a test lead direct between battery and pump?
Click to expand...

Thanks but...
Next to the water ballasting pump is the diesel ballasting pump which works fine. Swapping supplies does not solve the problem. So we can rule out electric supply.
 
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Thanks for help so far, by way of update....

I have checked the 12v supply and all is good.
I have removed a blanking plug on the output side on the top of the impeller casing body to eliminate any “blockage” downstream of the pump. Water can exit from here. So blockage/ airlock back pressure is ruled out.

The symptoms still persist.....

When turned on the pump runs for less than two seconds then stops, then runs for less than a second then stops then runs for less than a second then stops altogether.
Leave for 10 mins and the sequence can be repeated.
I think this has to be a motor issue not producing sufficient torque.

Hopeully will get an a response from Johnson but if not will strip the pump.

Thanks
 
Dave100456 said:
Thanks for help so far, by way of update....

I have checked the 12v supply and all is good.
I have removed a blanking plug on the output side on the top of the impeller casing body to eliminate any “blockage” downstream of the pump. Water can exit from here. So blockage/ airlock back pressure is ruled out.

The symptoms still persist.....

When turned on the pump runs for less than two seconds then stops, then runs for less than a second then stops then runs for less than a second then stops altogether.
Leave for 10 mins and the sequence can be repeated.
I think this has to be a motor issue not producing sufficient torque.

Hopeully will get an a response from Johnson but if not will strip the pump.

Thanks
Click to expand...

Just a thought. Have you monitored thee voltage at the motor terminals while it is behaving as you describe? A big fall from the system volts might indicate a poor connection or other resistance in the supply or negative return
 
Email response from Johnson Pumps

“Your information was forwarded to our application engineer. He said that he has had a similar issue with some OEM pump applications and finds this can be a contact issue in the electrical motor connections in the rear of the motor where the torque causes the motor to 'give up" under load. ”

One year warranty expired so nothing to be lost in stripping motor to investigate.
Hopefully will be able to replace just the motor rather than motor and bronze housing together.
 
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