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Old 14-05-2013, 14:05   #1
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Air in water system problem

My 9 month old boat has had a problem since new that no one has been able to fix. It's not that they haven't tried. The builder, the pump manufacturer have all tried many times but still the problem persists. I have left on a cruise to North Qld with the problem because no one was making any progress and I thought that if I waited until it was fixed I might never get away.

The problem is that the house water supply continually gets air in it and it won't self prime. The pump which is supposed to shut off when the accumulator reaches set pressure, runs continually because it can't prime itself and therefore can't build up pressure in the accumulator. We can prime the pump by opening a faucet and running water down the drain and when we do this the accumulator begins to build pressure and then shut off. But after a while the system loses pressure and we find the pump is running again. Let me describe the system. We have four integral water tanks of approx 300 litres each built into the bilge. water is drawn through into a bank of valves (similar to a manifold) that lets me select from which tank I want to draw. A manual foot pump (which works perfectly) is teed into this same valve bank. It then passes through an inline filter to the pump which is mounted above the tanks (pump supplier tells me this is not a problem for this pump). From the pump it feeds into the attached accumulator and from there to the various parts of the boat including the head, deckwash, galley, stern shower and hot water system. I think I have tried all the logical remedies like checking for kinks in hoses, tightening all clamps etc, even changed out the pump.

Please, any ideas from the experts at CF?
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Old 14-05-2013, 14:47   #2
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Re: Air in water system problem

If the builder, and the pump manufacturer can't find the problem, it's going to be pretty hard for people who have never seen the boat to offer you a solution.

You say you have four water tanks and you can draw from any of these. Do you have the problem regardless of which or how many tanks are online? If so, the problem is upstream of the tanks and manifold.

The only way for air to get in the lines is through a leak. Since it's on the suction side of the pump, air is leaking in, water is not leaking out so there will be no puddle to help you find the leak.

I suggest taking the manual pump our of the system as a first step. Other than that, check or re-do all connections one at a time until the problem is solved. You could also have a hole or crack in one of the water lines between the manifold and the pump. It's not far fetched to imagine someone at the factory accidentally running a screw into a water line.
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Old 14-05-2013, 17:00   #3
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Re: Air in water system problem

G'Day Vic,

There may well be an issue with air getting in past the check valve in the foot pump. A quick check is to carefully plug the spigot on the foot pump so that no air can get in and then see if your symptoms are gone.

We have a similar intermittent problem on I-2 with a foot pump and a Fynspray hand pump on the same circuit... not quite analogous, but possibly related.

Good luck and watch out for the jet skis and the Rivieras!

Cheers,

Jim
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Old 14-05-2013, 17:10   #4
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Re: Air in water system problem

Try useing a bicycle pump hooked up to your system, sometimes only a little pump up will show you your air leak !! it has worked for me a couple of times in the past ! Just a thought
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Old 14-05-2013, 18:03   #5
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Re: Air in water system problem

Agreed that it could be a dodgy foot pump letting air in. It also could be the filter on the pump inlet if its partly clogged and not letting the pump build up pressure. If the foot pumps check out fine, then remove the filter in the inlet and replace with a coupling and see if that it.

If it was my boat I would have the pump located with a flooded suction. The filter adds too the pressure drop making the pump work harder.

Does the pump have O-ring seals on the nozzles where the hose connects to the pump. Last it could be a bad pressure switch.
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Old 15-05-2013, 01:11   #6
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Re: Air in water system problem

Thanks for your input everyone. I have tried most of the ideas except Bob's idea with the bike pump. I can't give it a go for a few days, but I will report back the results after I have searched a bit more. Thank You.
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Old 15-05-2013, 01:17   #7
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Re: Air in water system problem

You'll need to remove (plug) components from the system and start with the pump drawing from a hose in a bucket. Then add (reconnect) components one at a time while continuing to test. Assume nothing.
Auto repair tool suppliers have some great hose clams that stop the flow temporarily and don't damage the hose.
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Old 15-05-2013, 03:05   #8
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Re: Air in water system problem

I have had the same problem on occasions with our Athena particularly after a rough sail with half full tanks. The temporary fix I have used to get it running properly again is to crack the inlet to the pump and drain off a little water and presumably air, whereupon the pump works normally. The only solution I can think of is to tee into the pump inlet line at its highest point near the pump and run a vent pipe up (and without dips) so its end is well above the tank's highest point (fitting a filter on the end to prevent critters and other contamination getting in). That should allow any air in the inlet pipe to bleed off.
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Old 15-05-2013, 03:18   #9
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Re: Air in water system problem

A faulty check valve(non return valve) is another common problem with pressure systems. This should be fitted next to pump and it's role is to maintain the pressure once the pump has reached it's desired pressure. If it is letting water pass backwards the water will run back to your holding tank and your pump will run again until pressure is reached, if ever.
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Old 15-05-2013, 05:05   #10
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Re: Air in water system problem

Quote:
Originally Posted by Rapanui View Post
... The only solution I can think of is to tee into the pump inlet line at its highest point near the pump and run a vent pipe up (and without dips) so its end is well above the tank's highest point (fitting a filter on the end to prevent critters and other contamination getting in). That should allow any air in the inlet pipe to bleed off.

Does the water supply, to the pipe, rise up above the pump, then down to the pump inlet, creating a high point (inverted ‘U’)?
If so, you may want to install an Air Release Valve.
Air Release Valves function to release air pockets that collect at each high point of a pressured water line.

See ➥ Air Release Valves
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Old 15-05-2013, 06:51   #11
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Re: Air in water system problem

Quote:
Originally Posted by bobconnie View Post
Try useing a bicycle pump hooked up to your system, sometimes only a little pump up will show you your air leak !! it has worked for me a couple of times in the past ! Just a thought
You have to be very careful with this method. You can easily cause more damage by over pressurizing sections of the system that were not meant to be pressurized. This might hurt you in the long run.

Instead I would recommend you isolate one section at a time and put it under vacuum. Disconnect both ends of a run, plug one end with a cork or rubber stopper then draw a vacuum using a small hand pump. It should hold a vacuum for at least 10 minutes.

When you find the section that doesn't hold a vacuum, remove that section and inspect it closely. When you find a hole or damage, photo it and keep it to bring to the dealer. Make them give you some cool accessory for your boat for doing their job for them.
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