Jabsco fresh water pump pulsating?

[Cardo]

We have an old Jabsco Par-Mate 2.5 GPM fresh water pump. I don't know how old it is, but it has been working fine for the last year and a bit, since we got the boat.

However, its behaviour has changed, and I'm wondering whether is has developed a fault or something?

Before, when we ran a tap, the pump would run slowly or quickly, depending on how much you opened the tap. However, now instead of running slowly, it pulsates. This happens until you get to a fairly high water flow, at which point it'll run continuously and speed up a bit up to the max. Most of the time it will be pulsating, unless we're filling a bowl, or the kettle, etc.

Any thoughts what could cause this? I have made changes to the water system over the winter, installing a separate foot pump tap from the non-pressurised side, adding another water tank, and also another T-off from the pressurised side to service the watermaker. However, the pulsating symptoms only seem to have started more recently, and not just after the changes.

Thoughts?

 

[l'escargot]

Have you added an accumulator? With more than one take off you should have one - in fact even with only one take off it is best to put one in a pressurised system.

If you already have one it sounds like you need to replace the diaphragm or recharge it with air depending on the type.

 

[winsbury]

Had something similar on a motor home once - turned out one of the hot water pipes behind a bulkhead was gradually slipping off the tap spigot making the pressure pulse each time it moved a fraction until one day - pop , splosh & uncontrolled pumping until he tank ran dry !!!!... not good. Check all your hoses are tightened and have clips on and also have no weak spots that could be expanding prior to a burst.

 

[geem]

Has your accumulator membrane failed? You can check this by depressing the valve. If water comes out instead of air it's failed

 

[Cardo]

We don't have an accumulator on the system (unless the calorifier counts!). We didn't have one before, either, and it didn't pulsate. What could have caused this to start suddenly?

I have checked and double checked all the hoses recently, as part of making sure the changes I made are holding ok.

So, should I fit an accumulator? And where does this go? Straight after the pump, I presume? We have one on the watermaker pump to smooth that out. I presume it's the same thing?

 

[l'escargot]

We don't have an accumulator on the system (unless the calorifier counts!). We didn't have one before, either, and it didn't pulsate. What could have caused this to start suddenly?

I have checked and double checked all the hoses recently, as part of making sure the changes I made are holding ok.

So, should I fit an accumulator? And where does this go? Straight after the pump, I presume? We have one on the watermaker pump to smooth that out. I presume it's the same thing?

"Accumulator Tank Info - from Jabsco ITT

WHAT ACTUALLY IS AN ACCUMULATOR TANK (AND WHAT DOES IT DO)?
Most people know that a water pressure system relies on the presence of an accumulator tank to function properly but few actually understand what it does. They function on the principle that air will compress under pressure whilst fluids will not. An accumulator is an air filled tank that half fills with water as the pump operates. When the pump is turned off the system has a store of water in the tank which is under pressure from the compressed air. This means that, depending on the size of the tank, you can run off a quantity of water without the pump needing to cut in, particularly handy if the pump is installed immediately below a bunk occupied by a tired crew member!

Accumulators will also release their store of pressurised water if demand on the system exceeds pump capacity, the larger the tank the more water in reserve.

Finally, the air acts as a cushion, absorbing pressure fluctuations and vibrations. This quietens the whole system and allows the pump's pressure switch to reach cut-off pressure cleanly, lengthening pump, motor and switch life.

Where a boat has a simple tank without a bladder to separate the air and water do remember to drain the tank down at least once a season, the air tends to get scoured out and eventually the tank will be full of water and serving no useful function at all!


TROUBLESHOOTING A WATER PRESSURE SYSTEM
Marine water systems are now more technically advanced than ever and should give many years of trouble-free life. However, problems can occur and the following guide to some common complaints may help:

FAILURE TO PRIME can be caused by an air leak in the intake or discharge line, a blockage in the inlet pipework, punctured diaphragm, debris under the valves or a crack in the pump housing.

PUMP FAILING TO TURN ON can be caused by poor wiring or loose connections, blown fuse, or defective pressure switch or motor. Check that there is full voltage available at the pump before investigating other causes.

A PUMP FAILING TO TURN OFF is normally because the switch cannot reach its cut-off pressure. This can be caused by simply having an empty water tank but other causes can be a punctured diaphragm, debris under the valves, leaking pipework, insufficient voltage or a defective pressure switch. Clean inlet filters and check valves and diaphragms, if they are worn now is the time to replace all wearing parts.

PUMP CYCLING ON AND OFF WHEN NOT IN USE is most commonly caused by small leaks in the pipework or a tap left dripping allowing the pressure to slowly reduce to the pump's cut in point. Tighten all loose connections after racing the source of the leak.

PUMP CYCLING ON AND OFF DURING USE is normally caused by a restricted delivery, check and clean filters and all pipework for restrictions to flow including undersized pipe. Fit an accumulator if one is not fitted.

LOW FLOW AND PRESSURE may be just that the pump is undersized for the system. Check the manufacturer's recommendations. However, deteriorating pump performance can be caused by an air leak at the pump inlet, accumulation of debris or scale within the pump and pipework, worn valves and diaphragm, low voltage or defective motor.

Low voltage due to inadequate cable size being used is a common cause of pump problems, always follow the cable size recommended in your data sheet. Checking that correct voltage is available can only be done by measuring voltage at the pump when it is running.

INCREASE THE LIFE OF YOUR WATER PRESSURE SYSTEM
Most boat owners leave their boats at the end of the weekend and sensibly turn off power to the pump. However, pump life can be increased by also opening the taps to relieve pressure in the system once power is off. This depressurises the system saving wear and tear on diaphragms and valves when not in use."

I would wonder about having one off a t to the watermaker, is that recommend? I would have thought one just after the pump would cover the whole system, including the watermaker - they are usually installed immediately after the pump.

 

[vyv_cox]

Unfortunately I don't entirely understand your description 'pulsating'. Can you describe the problem a little more clearly?

There is no specific need for an accumulator. As the name suggests, all it does is to store pressure so that when the tap is opened the pump need not start immediately. When it does start it only tops up the accumulator, so does not run continuously when the tap is open. My boat, as built, did not have one and had been operated for many years perfectly successfully.

 

[Cardo]

Unfortunately I don't entirely understand your description 'pulsating'. Can you describe the problem a little more clearly?

There is no specific need for an accumulator. As the name suggests, all it does is to store pressure so that when the tap is opened the pump need not start immediately. When it does start it only tops up the accumulator, so does not run continuously when the tap is open. My boat, as built, did not have one and had been operated for many years perfectly successfully.

By pulsating I mean the pump cycles on and off, causing water to come out in spurts. This only happens when taps are opened a little. When opened fully or nearly fully the pump runs continuously.

The above quote by L'escargot would suggest there may be a restriction, however I don't see how it would then work fine when the tap is open fully?
It may just be that with all the changes to the water system, an accumulator may help even out the pressure. Or maybe just ignore it, but I'm concerned with damaging the pump by having this cycle so much.

 

[Tony Cross]

By pulsating I mean the pump cycles on and off, causing water to come out in spurts. This only happens when taps are opened a little. When opened fully or nearly fully the pump runs continuously.

The above quote by L'escargot would suggest there may be a restriction, however I don't see how it would then work fine when the tap is open fully?
It may just be that with all the changes to the water system, an accumulator may help even out the pressure. Or maybe just ignore it, but I'm concerned with damaging the pump by having this cycle so much.

I think the pressure switch on your pump is failing. At low tap openings it's switching off under the tiny back pressure of the partly opened tap, but because the tap is still open the pressure reduces and the switch turns on. At full opening there is no back pressure in the pipework and the switch stays off.

Generally there is a diaphragm held against a spring that operates a micro-switch. If the spring has weakened or failed you'll see the effects you mention I reckon.

 

[maby]

By pulsating I mean the pump cycles on and off, causing water to come out in spurts. This only happens when taps are opened a little. When opened fully or nearly fully the pump runs continuously.

The above quote by L'escargot would suggest there may be a restriction, however I don't see how it would then work fine when the tap is open fully?
It may just be that with all the changes to the water system, an accumulator may help even out the pressure. Or maybe just ignore it, but I'm concerned with damaging the pump by having this cycle so much.

In my experience, most boat water systems work like that - the only difference is the frequency of the pulsing. Think about it - the pumps are relatively simple devices - single speed with a pressure switch to turn them off. When you first turn on the power, the pump will run until the pressure in the pipes is high enough to trip the switch then, assuming no leaks, it will stay off till you open a tap. Water is not very compressible - in the absence of an accumulator, the pressure will drop quickly and the switch will close, letting the pump run. if you have the tap wide open, water may flow at a rate determined by the pump capacity and the pump will run continuously. If you don't draw water rapidly enough, the pump will push the pressure up enough to open the switch, but with little room for compression, the pressure will quickly drop again and the whole cycle repeats.

The accumulator is a cylinder that you connect into the water system somewhere close to the pump and which contains some mechanism to provide some expansion capacity. Some are just air chambers and must be installed vertically, others contain some sort of diaphram and can be installed in any orientation. When the pump runs, it either compresses the air in the accumulator or stretches the diaphram - in either case, it gives you some stored pressure and increased the cycle time for the pump, smothing out the delivery of water.

The symptoms you describe go with an accumulator that has either failed, or needs to be recharged with air. If you are correct in saying that you don't have an accumulator fitted, then it's hard to see how the behaviour of the system could change. The only thing that springs to mind is an excessively sensitive pressure switch in the pump?

 

[vyv_cox]

I think Tony's diagnosis is pretty close, although a partial blockage or a kinked hose might do the same. On some pumps the pressure switch only pushes into place and you may be able to push it back in, depends on the model. Ignore all the talk of accumulators, nobody needs one, it just makes water pumping less noisy.

 

[l'escargot]

Ignore all the talk of accumulators, nobody needs one, it just makes water pumping less noisy...

... and will stop pulsing on partially opened taps...

I am still suspicious of the accumulator being fitted tee'd off to the watermaker further down the system away from the pump.

 

[Cardo]

... and will stop pulsing on partially opened taps...

I am still suspicious of the accumulator being fitted tee'd off to the watermaker further down the system away from the pump.

I feel I may have introduced a red herring mentioning the accumulator on the watermaker. This is on the raw water inlet pump that's used to create fresh water. It is not part of the fresh water system. I just used it as an example as the watermaker pump doesn't cycle, just runs at a constant speed.

I have been advised by Jabsco that the behaviour I'm experiencing/explaining is par for the course. However, my pump is at least 13 years old, so it may be worth having a new one as a backup!