Fresh water system airlock

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gwebster

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I have a dufour 41 with a pressurised fresh water system for the galley and two heads.
A jabsco parmax 3 pump and jabsco 1 litre accumulator tank are followed by a small, simple mesh filtre.

The hot water boiler is a 40 liter Quick, heated by electric immersion from the 240 volt and by the engine by heat exchange.

It has been fine for 10 years since new, then, this season, we have constant airlocks , i.e. spluttering from the taps with only little water flowing, which can be cleared by pumping the footpump, but only for a few minutes.

I replaced the pump, then the accumulator tank. Then we found that the pressure valve on the boiler was dripping so I replaced that. Still no joy.

We are finding a tea cup full of water, maybe with a little anti freeze in it, in the bilge daily.

I am thinking there must be a leak somewhere which allows air into the system when the pump is running.

Any ideas, anyone??
 
The system will only draw in air between the tank and the pump. After the pump the pressure is far higher than atmospheric, so water could leak out but not air in. I suggest you have a loose connection at the pickup in the tank, or maybe at the pump connection itself.

There is not a lot of point in having a filter after the accumulator. A wire mesh strainer should be sited before the pump to prevent debris from the tank from getting into it.

Antifreeze in the bilge has to be coming from the engine circuit. It can be that domestic water is leaking into the calorifier through a perforation but this will not introduce air. I wrote an article on this for a recent PBO (Summer 2012?) which might give you some clues.
 
Brilliant, thanks, I will look there at the connections.
As for the leak of antifreeze, it doesnt seemt o come from the engine so it may be that I need a new calofier. I have a 40 litre round oil barrel shape by Quick in Italy. Do you know of one which might fit in the same space?
 
airlock in fresh water system

I seem to have solved this ongoign problem , since the start of this season. It turns out to be the manual footpump/ tap which is allowiing air to be sucked into the system. So having replaced jabsco pump, expansion tank and hot water boiler, when it still didnt work, the engineer put his finger over the tap from the manual foot pump, and that stopped the pump working, i.e. that was the source of the airlock.

Does anyone know how the manual system normally prevents air being drwan in when the electric pump is operating?

Thanks for comments so far.
 
Presumably the manual pump is a typical displacement type with a membrane or piston and two valves, suction and discharge. The valves open to allow water to pass forwards and close to stop it going back. If the pump is letting air back the valves are either broken or held open by debris.
 
gwebster said:
I seem to have solved this ongoign problem , since the start of this season. It turns out to be the manual footpump/ tap which is allowiing air to be sucked into the system. So having replaced jabsco pump, expansion tank and hot water boiler, when it still didnt work, the engineer put his finger over the tap from the manual foot pump, and that stopped the pump working, i.e. that was the source of the airlock.

Does anyone know how the manual system normally prevents air being drwan in when the electric pump is operating?

Thanks for comments so far.
Click to expand...

Mine has a stop cock just before the tap.
 
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