Another broken water pump question...

[BlueStringPudding]

Something I'm curious over is my funny ole water pump. The previous owner had fitted an isolation switch for it in the galley, presumably because of a leak in the system. And sure enough when left on the pump would cycle once every hour or two. In recent months it became apparent that the self-filling header tank valve was the source of a/the leak. (You could hear it filling unnecessarily and also see the header tank overflow pipe continuously dripping in the stern bilge. Even when the height of the ballcock was adjusted there was the same problem) So I had that valve replaced a couple of weeks ago. And it's solved that problem.

 

Now if I leave the isolator switch to the water pump on and, say, a tap had been on and is then turned off, the water pump runs fast, slows down for a bit, then stays very slowly running for 30-60 seconds before finally cutting out. (At least it does cut out now the valve in the header tank has been replaced). Twice now I've noticed, unusually for my water system, that I can be away from the boat all day and then come home and turn a tap on and water comes out at proper pressure., even with the isolator switch off (until of course the head of water in the pipes runs dry) Not unusual for most people's boats but it is if you've been used to the system depressurising while the isolator switch is off. This leads me to believe that I have hopefully fully resolved the leak problem.

 

So my question is: why the "fast-slow-really slow drone" running speed of the pump? It's always done it but because it never cut out I assumed it was due to the leak. Now it does cutout eventually, is this actuallt an accumulator thing, do you think? Or is there a chance there's another leak or summit else wrong with the pump or system?

[Paul C]

Do you have a pressure gauge anywhere in the system?

 

Sounds like a suspect PRV to me. It might just be opening at a slightly lower pressure than it ought to; they can be cleaned by turning the knob on them (it forcibly opens/shuts the mounting faces of the valve).

 

PS Another solution might be just to tweak the pump pressure down a touch - most water pumps have a screw to adjust the pressure, although normally you'd not need to.

[by'eck]

So my question is: why the "fast-slow-really slow drone" running speed of the pump? It's always done it but because it never cut out I assumed it was due to the leak. Now it does cutout eventually, is this actuallt an accumulator thing, do you think? Or is there a chance there's another leak or summit else wrong with the pump or system?

 

Sounds like the pressure cut off switch on the pump is just a little lazy. Maybe clogged up a bit or if adjustable could be set a little high as suggested above.

 

This results in the pump continuing to pressurise the accumulator beyond the ideal, causing ever increasing load on the pump, so it slows gradually.

 

An alternative possibility is low voltage to the pump so it runs for longer, slowing down in the process as it struggles to reach the correct pressure. Checking the voltage at the pump whilst its running will confirm this scenario if its below say 12 volts.

[BlueStringPudding]

Do you have a pressure gauge anywhere in the system?

 

Sounds like a suspect PRV to me. It might just be opening at a slightly lower pressure than it ought to; they can be cleaned by turning the knob on them (it forcibly opens/shuts the mounting faces of the valve).

 

PS Another solution might be just to tweak the pump pressure down a touch - most water pumps have a screw to adjust the pressure, although normally you'd not need to.

 

No pressure gauge, nope. It's an ex hire boat, y'see.

 

Tweaking the PRV has never changed the way the water pump runs so I doubt it's that. Pump pressure maybe.

 

Thanks, By Eck. It hadn't crossed my mind that voltage might have something to do with it.

 

So chaps, where do I find the pressure adjusting thingy? And how far do I twiddle it? (Stop me if I'm dazzling you with my technical lingo)

[Paul C]

Screw is normally in the end of the pump, along its axis..

[BlueStringPudding]

Thanks. I'll have a look. (When I'm having a not-being-scared-of-potential-spiders day)

[bizzard]

Don't know what make pump this is but the adjusting screw is usually in the centre of the pressure switch at the pipe nozzles end of the pump and is either a Philips x screw or an Allen screw requiring an Allan key to adjust it. Mark its present position before adjusting so as to return it if it makes no difference.

[BlueStringPudding]

Ok thanks. Pretty sure mine, being a Black Prince boat, is a Jabsco pump

 

Not sure what a pressure switch looks like though but even I should be able to find pipe nozzles

[bizzard]

Ok thanks. Pretty sure mine, being a Black Prince boat, is a Jabsco pump

 

Not sure what a pressure switch looks like though but even I should be able to find pipe nozzles

Like a square box with wires coming out of it in between the nozzles. Screw clock-wise to raise pressure and anti-clock out to lower it, only move the screw about 1/4 turn at a time and try it.

[BlueStringPudding]

Thanks, Bizzard. That's clear. I'll take a look when I get a moment and report back my tweakings.

[Iain_S]

(snip)

Now if I leave the isolator switch to the water pump on and, say, a tap had been on and is then turned off, the water pump runs fast, slows down for a bit, then stays very slowly running for 30-60 seconds before finally cutting out.

 

Could it be a pump designed to run without an accumulator? I'm not really familier with them, but the blurb about them suggests that the pump speed varies with demand, which could explain the above symptoms.

 

Iain

[BlueStringPudding]

Thanks Iain. It's definitely got an accumulator coz I seen it. I assume the pump is the original from when the boat was a hire boat in the late nineties. In which case the set up is probably the same as the rest of the fleet was, so unlikely to be wrongly fitted with an accumulator. However there's no guarantee one of the later private owners didn't alter the set up themselves.

[bizzard]

Thanks Iain. It's definitely got an accumulator coz I seen it. I assume the pump is the original from when the boat was a hire boat in the late nineties. In which case the set up is probably the same as the rest of the fleet was, so unlikely to be wrongly fitted with an accumulator. However there's no guarantee one of the later private owners didn't alter the set up themselves.

I'd turn that pump switch off when your boats left unattended BSP or you might come home to a flooded out boat if a pipe springs a leak cos the pump will start and continue to empty the tank. I renewed the entire bathroom floor on a boat which had rotted because of that happening last year.

[BlueStringPudding]

I always do, biz. Out of habit of turning it off even when I'm on board for the last six years. but if I get to the bottom of the way the pump is running at the moment, I'll leave the switch turned on for longer and longer periods when I'm home to test whether it starts cycling again. It's actually very helpful having an isolator switch.

[bizzard]

I always do, biz. Out of habit of turning it off even when I'm on board for the last six years. but if I get to the bottom of the way the pump is running at the moment, I'll leave the switch turned on for longer and longer periods when I'm home to test whether it starts cycling again. It's actually very helpful having an isolator switch.

The pump doesn't sound like its behaving too badly,''I've got good ears'', probably just the newness still wearing off.

[BlueStringPudding]

[smileypete]

Usually there's a red wire going to the pressure switch, then a red wire from pressure switch to motor with a connection part way, then a black wire from motor back towards batt negative with a connection near the motor.

 

If you have a multimeter, try measuring the voltage across the motor, but while the pump is doing it's slow shut-off thing.

 

So the red probe goes to the connection on the red wire between pressure switch and motor, the black probe goes to the connection on the black wire coming from the motor.

 

If the connections are the 'push on' terminals they can be pulled apart a little to expose some metal.

Don't forget to use the correct sockets on the meter which are usually labelled V and COM.

 

cheers, Pete.

~smpt~

[adrianh]

As you say that you have an accumulator fitted, I would expect the pump to slow down a bit as the pressure increases towards the 'shut off' pressure setting.

Also,as the accumulator fills (compressing the air filled rubber bag inside it) the pump has to work harder to raise the water pressure, therefore the motor will need to draw more current from your battery. The more current that you pass through the wires supplying the pump the higher the voltage drop ( this is also proportional to the cable length), this will reduce the voltage at the motor which will also cause it to slow down a bit - this can be made worse if the wire sizes are to small.

It is not a good practise to adjust the pressure switch above the design pressure of the pump, as this could stall the motor, which can the get very hot and catch fire in the worst case ( make sure that the pump has a suitable fuse adjacent to it)

I have had problems recently with the internal non return valves of the pump (Shurflo)letting the water slowly return to the tank and have had to purchases spares. The design is very basic with a short operating life expectancy!

Edited March 27, 2013 by adrianh

[Higgs]

My thoughts on the fast speed sound turning to slow speed sound. The batteries on my boat are becoming a bit weak and, as the pump turns on, the pressure in the system is low building up to higher pressure.

 

At first the pump is fast with low pressure in the system, with the pump having to work less hard; as the pressure builds up the pump has to work harder, and depending on how well the electrics can deliver power to the pump under the increasing load, the pump will slow if it is becoming old or if the current isn't there to power the pump as the load increases.

Edited March 28, 2013 by Higgs

[IanM]

 

 

Now if I leave the isolator switch to the water pump on and, say, a tap had been on and is then turned off, the water pump runs fast, slows down for a bit, then stays very slowly running for 30-60 seconds before finally cutting out. (At least it does cut out now the valve in the header tank has been replaced). Twice now I've noticed, unusually for my water system, that I can be away from the boat all day and then come home and turn a tap on and water comes out at proper pressure., even with the isolator switch off (until of course the head of water in the pipes runs dry) Not unusual for most people's boats but it is if you've been used to the system depressurising while the isolator switch is off. This leads me to believe that I have hopefully fully resolved the leak problem.

 

So my question is: why the "fast-slow-really slow drone" running speed of the pump? It's always done it but because it never cut out I assumed it was due to the leak. Now it does cutout eventually, is this actuallt an accumulator thing, do you think? Or is there a chance there's another leak or summit else wrong with the pump or system?

 

To me what you describe there is just the pump charging the accumulator up before switching off. It's what ours does

[BlueStringPudding]

To me what you describe there is just the pump charging the accumulator up before switching off. It's what ours does

 

Does it? I've never heard anyone else's pumps do that when I've been on their boats. But maybe it's something particular to yours/my type of pump. It does seem odd though, the third part of the pattern, the very slow constant running for 30-60 seconds before finally clicking off.

[smileypete]

Sometimes the slow running isn't good for the pressure switch as it can oscillate on and off excessively, reducing it's life.

 

A workaround is to unscrew the screw in the middle of the pressure switch 1/4 turn at a time, noting it's original position. That said this won't cure a low voltage at the pump motor, caused poor or failing connections.

 

ETA If you switch off the pump and open the tap into a bowl, that should tell how much water the accumulator is taking in.

 

cheers, Pete.

~smpt~

Edited March 28, 2013 by smileypete

[Paul C]

Easy check for low voltage - try it with the engine running. Then it gets something like 14.2V instead of 12.6V (before any voltage drop across the wires that supply current to the water pump).

 

The reason I mentioned pressure gauge is it makes diagnosing things easier, otherwise you can end up just guessing which component(s) have failed or aren't working quite right.

[BlueStringPudding]

Good point Paul. It does the same thing with the engine running.

 

Sometimes the slow running isn't good for the pressure switch as it can oscillate on and off excessively, reducing it's life.

 

A workaround is to unscrew the screw in the middle of the pressure switch 1/4 turn at a time, noting it's original position. That said this won't cure a low voltage at the pump motor, caused poor or failing connections.

 

ETA If you switch off the pump and open the tap into a bowl, that should tell how much water the accumulator is taking in.

 

cheers, Pete.

~smpt~

 

Thanks smiley. Why do I need to know how much water is in the accumulator?

 

By the way, my original fears were confirmed. There WAS a spider waiting to get me by the water pump.

[MtB]

Now if I leave the isolator switch to the water pump on and, say, a tap had been on and is then turned off, the water pump runs fast, slows down for a bit, then stays very slowly running for 30-60 seconds before finally cutting out.

 

Coasty's pump started doing that last summer. it isn't right and it sounds awful. I suspect the microswitch in the pressure switch goes high-resistance as the pressure rises and it is on the cusp of switching, leading to reduced current in the pump motor.

 

The fix was easy. I fitted a new pump purchased on ebay.

 

MtB