PDA

View Full Version : Intermittent pump fault



Stustoys
25th Aug 2019, 12:15 PM
I have a house pump that occasionally either starts slow(the water doesn't start to flow for a few seconds after the tap is turned on) or doesn't start at all(the controller then trips and needs resetting). Of course trouble shooting it is pretty much impossible as it always starts when I am standing next to it. My first guess is the cap is on the way out. Sound reasonable, and better ideas?

Secondly the cap is 12uf +/-5%, the only (almost) direct replacement I can find is +/- 10%. Would I be correct in assuming that will make stuff all difference?

Thank you

BobL
25th Aug 2019, 01:25 PM
I have a house pump that occasionally either starts slow(the water doesn't start to flow for a few seconds after the tap is turned on) or doesn't start at all(the controller then trips and needs resetting). Of course trouble shooting it is pretty much impossible as it always starts when I am standing next to it. My first guess is the cap is on the way out. Sound reasonable, and better ideas?

Secondly the cap is 12uf +/-5%, the only (almost) direct replacement I can find is +/- 10%. Would I be correct in assuming that will make stuff all difference?

Thank you
Yes.

Even more so if it's a start cap.

BaronJ
25th Aug 2019, 06:36 PM
Hi Stustoys,

If it has a centrifugal switch, check that the contacts are clean and in good order. If it just has a capacitor and no centrifugal switch then yes the cap would be suspect. The tolerance of +- 10% is immaterial for a motor.

I would check the switch first, in fact any switch that was in circuit, since the inductive arc will cause switch damage over a long period of time.

Stustoys
25th Aug 2019, 08:09 PM
Hi Guys,

Thanks for that.

I should have included more details.
It is a run cap.
link to said replacement. https://www.ebay.com.au/itm/271463063489

Its the same manufacture(not a huge issue but at least the package is the same size)
It has leads, mine has terminals.(not an issue)
There are similar ones available with 5% but their V rating is lower, I assume they are meant for starter caps.
https://www.ebay.com.au/itm/281317085292

malb
25th Aug 2019, 11:35 PM
Your problem could be caused by issues other than the cap in the motor, and there isn't a lot of detail about the application given.

Older style pressure pumps with the bulbous cylinder use a bladder in the cylinder and rely on air pressure in the bladder to regulate water pressure while the pump is not running, to reduce the number of stop start cycles the motor experiences. If the bladder becomes waterlogged or looses pressure for some reason it can affect starting at times and cause intermittent problems.

If the pump housing is having solids enter it with the water, residues may be building up in the housing and jambing the impeller or adding enough extra friction to cause a slow start. It's also possible that small solids are occasionally blocking the entry port to the pressure switch so that the unit does not clearly sense a drop in pressure when a tap is opened. If the pump is an automatic type pump, it might pay to check the entire system rather than just blame the run capacitor and replace it. As suggested at the top, there isn't a lot of info about pump and it's water source, just an initial surmise that the cap is bad.

Toggy
26th Aug 2019, 08:44 AM
Simon,

Sounds like the pressure switch. They have a small port leading to a rubber diaphram where pressure activates the cut in/cut out springs. The port can block with debris and the spring mechanism can collect crud, and with age wear and jam. Replacement available from farm irrigation outlets. Last one I replaced cost somewhere around $125.

Ken

Stustoys
26th Aug 2019, 11:17 AM
More missing details ;)

No pressure tank.
Anything going into the tank goes through 1mm screen.
Pump inlet has a 250 micron screen.

The two times that the pump hasn't started, the controller has known the pump hasn't started and signaled a fault. So I assume that side of things is working(short of the motor control relay not working correctly). I have a another controller though of course it is a 90 degree one and the current one is straight through, I could make it work though custom plugs make life harder.

If I had a web cam with descent audio I'd try setting that up.
If it would stop working life would be so much easier :D

Thank you

BaronJ
26th Aug 2019, 06:03 PM
Hi Stuart,

Yes its very hard to diagnose an intermittent fault when it won't occur to order. :D

Your controller probably looks for a loss of pressure before it times out and shows a fault.

FWIW. Pressure switches can be obtained from automatic washing machines. They are used to set water levels and prevent the heater coming on without water. In a washing machine they use air pressure to measure the water level.

Toggy
26th Aug 2019, 06:43 PM
Stuart,

Sounds like you have an 'even flow' switch. My house pump has one and it goes on the fritz in hot weather (usually well over 40C). I bought a replacement but found that the original would still work if I turned the power off for a while then activated the switch reset button after powering on.

Ken

Stustoys
27th Aug 2019, 11:27 AM
Your controller probably looks for a loss of pressure before it times out and shows a fault.

As I understand it these controllers use a water wheel to measure flow. They trip when they sense no flow, to save the pump from running dry(granted not the issue in this case but it doesn't know that lol).


Sounds like you have an 'even flow' switch.
No, my pump is either on for off.


Had another fail to start, but this time the pump didn't start with the first push of the reset, just hummed. Second press it started. I'm going with the cap. Yes it could be a few other things but having spare wont hurt and it is by far the easiest/cheapest thing to try. Not my favorite way to fix things but it will have to do.

BaronJ
27th Aug 2019, 06:09 PM
Hi Stuart,



Had another fail to start, but this time the pump didn't start with the first push of the reset, just hummed. Second press it started. I'm going with the cap. Yes it could be a few other things but having spare wont hurt and it is by far the easiest/cheapest thing to try. Not my favorite way to fix things but it will have to do.

What you are describing is a bad centrifugal switch, or a bad switch somewhere in the circuit, a bad capacitor doesn't behave like that ! Capacitors loose value over time or go open circuit completely, where as a switch contacts will arc and burn becoming intermittent before becoming completely open circuit.

Sometimes you can smell the odd phenolic odour from a failing switch.

Stustoys
27th Aug 2019, 09:44 PM
Hi Baron

What you are describing is a bad centrifugal switch,
Well it could be if I had one, which I don't think I do.(though I haven't had the pump apart, so its just a guess. Haven't heard one)
Wouldn't the type, V rating and uF of the cap indicate that it is a run cap not a start cap?


or a bad switch somewhere in the circuit,
It could certainly be a bad relay in the controller.
Controller is harder to change as the manufacturers like to use different plugs between the controller and the pump, it goes without saying my spare pump has a different plug.


a bad capacitor doesn't behave like that ! Capacitors loose value over time or go open circuit completely,
I'm hoping the cap value went low enough to be the issue as I ordered a cap after my last post. I'll test the old one once I get it out. Thanks anyway. At least SWMBO thinks I am doing something ;)

BaronJ
28th Aug 2019, 01:54 AM
Hi Stuart,

A cap start and run motor doesn't always have to have a centrifugal switch in there. However you will find out when you change the capacitor. :U

Let me know how you get on.

Stustoys
31st Aug 2019, 01:30 PM
Cap changed.
New cap measures 12.27uF ESR 0.02ohm
Old cap measures 1594nF ESR 0.34ohm

The self healing must have given up ;)

Now to wait and see what happens.

BaronJ
31st Aug 2019, 08:55 PM
Hi Stuart,

Wow that capacitor has lost value, 1.5 uf nearly 1.6, the ESR has risen a lot by the looks of it as well.

Thanks for the update.

Stustoys
1st Sep 2019, 11:51 AM
No worries. It's the first time I've to used my LCR-T4 tester for something useful. Seems like a handy piece of kit.