Air in fresh water system

[Reefgeorge]

I have developed a problem where I have significant air in the fresh water system of my 2002 Cabo 47. I have a 24V and 120V water pump in parallel with Whale fittings and pipe throughout. Some have suggested that Whale fittings are not appropriate on the suction side from the tank to the pumps. Could this be my problem? Any other suggestions on where to start before I climb down there and start looking for the problem.

Thanks,

George

 

[bobk]

I went though this with my 1981 48MY when the tank level was low and the water had to be lifted further. I could not find the leak, but solved the problem with a check valve placed very close to the tank fitting.

Bobk

 

[GJH]

Yes, the check valve(s) between the pumps and the tank is the first suspect. I have a similar set up to your with two pumps, AC and DC. My Hatteras came with an OEM check valve right at the tank which had failed with age; replacing it solved a similar problem. This keeps all the water in the line up to the pump (and it's typical suction side check valve) from flowing back into the tank and losing prime or introducing lots of air. Without a diagram or pix, I can't se why the Whale fittings in and of themselves would be any problem at all unless you have a leak.

Nice boat, by the way, and welcome to the forum !

 

[Fanfare]

You may have a pinhole leak in the piping on the suction side of your pump. Or, if you have the PAR diaphram pumps you may have developed a tiny wear hole in the rubber diaphram. Even if you have two pumps such a hole in one diaphram can admit air to both. Try disconecting the intake to one pump at a time, put a layer of duct tape over the inlet, then reconnect and tighten hose. This will seal the diaphram off. See if the other pump still sucks air. Reverse and repeat.

 

[robertm]

Could someone please post a diagram of the correct routing of pipes and valves for a 120/240 volt and 32 volt pump setup for fresh water supply? Our PO apparenty rigged some kind of setup using pvc pipe, hose and a small 32 volt pump, but subsequently removed it. We are trying to return this boat to an OEM style set-up. I ahve a 120/240 volt pump installed and working and a 32 volt MR10 Galleymaid pump that is off the boat that I would like to install. Thank you.

 

[Reefgeorge]

Some good suggestions, thank you.

Another thought occured to me today. Sometimes when I open the cap to fill the water tank I hear gurgling for a few seconds as if pressure is being equalized. This might be a plugged vent line. Is there a check valve in the vent line or is it simply a connection at the top of the tank going up to the external fitting?

George

 

[bobk]

Some good suggestions, thank you.

Another thought occured to me today. Sometimes when I open the cap to fill the water tank I hear gurgling for a few seconds as if pressure is being equalized. This might be a plugged vent line. Is there a check valve in the vent line or is it simply a connection at the top of the tank going up to the external fitting?

George

I get something similar, like a suction in the fill line, every time I open the fill cap. Never figured it out, but think it might be water in a high vent loop. Thoughts?

Bobk

 

[bostonhatteras]

Just some food for though. I had the same problem and it turned out to be the solder that held the copper pick up tube to the tank fitting. After 40 years it had developed a leak and the warrantee had run out! I simply resoldered the copper tube to the fitting and the air/ vacuum problem disappeared. Btw I have been running shurflo Extreme 5.7 pumps for a few years now and I am glad I bought the extended warrantee at west marine. I have had only one of these pumps last past two years ! But now I get them for free because of the extended warrantee so I don't care too much. When it died July 3 rd though that sucked.

 

[Reefgeorge]

The first thing that I wanted to check was a functioning water tank vent. Ran the pump with and without the fill cap installed and there was no change, still air in the system in both cases. Then I started filling the water tank and there was a measurable amount of air being displaced out of the vent. This all suggested a functioning vent pipe. Then I reasoned that I should make sure that the vent pipe is clear of any partial blockage so I sealed the fill pipe while running full city water pressure with a full tank but nothing out of the vent. When I released the seal at the fill cap the water shoots up like Old Faithful implying pretty good pressure in the water tank. The vent is essentially at the same level as the fill cap and in days of old the water would spit out of the vent as the tank and fill hose would fill to the top. I cant figure out why I am getting air displacement at the vent during a passive fill but don't get water spitting from the vent anymore at the end of the fill and cant even get the vent to push water out when I pressurize the tank at the fill cap.

Is the tank vent a simple hose from the top of the tank to the outside vent opening or are there check valves, anti-syphon structure, etc.?

Any other thoughts?

George

 

[bobk]

You might have a delamination in the vent hose which is flapping over to shut of water flow, but allows air through. Pull it off at both ends if you can and run water directly from a hose in both directions. You might even see a flap when you pull it.

Bobk

 

[bostonhatteras]

If it is a fiberglass tank don't forcibly fill it! If the pressure has no where to go, the tank may bulge and break. In my boat, the water tank is glass and serves as a base for the plywood engine room floor. I did the same thing you were doing during recomissioning, running all faucets while overfilling the tank. I found the engine room floor pushed up in one corner about 3 inches! After this event the vent line would no longer purge excess water. I have since simply cut the vent hose and it overflows into the center bilge. When the tank is full the bilge pump goes on. Works for me. Why don't you configure a way to pressurize the pick up side of the water line and see where you get a leak.

 

[Reefgeorge]

Here is an update:

Pressurizing the water tank during a fill (with a cupped hand) did seem to clear the vent tube because now I get water spurting out of the vent at the end of a fill and no suction noise when the fill cap is removed. That however did not fix the problem.

I removed the plumbing after the check valve and the water free flows through the check valve from gravity induced pressure from the filled tank so that does not seem to be an issue.

2 of the 4 o-rings in the 24V quick connect pump assembly (backer board, pump, and accumulator tank) were leaking at rest so I replaced the assembly and that solved the obvious air in the system so there was a suction leak.

The 120 Headhunter pump still cycled and shut down even though I had good pressure and flow and no obvious additional suction leaks. I took all whale fittings and strainers apart and did find some silicone sealant particals in the fittings. The boat mnfg had added clear sealant to all suction fittings which broke up and got wedged in the fitting o-rings from frequent r&r. That said, no change in behavior. Then I found out by complete accident that if I pressurize the system first with the 24V pump, then the 120V pump works perfect. It pressurizes and turns off as intended and never shuts down on cycling no matter what the water demand circumstances are. The pump mnfg does not know why this works or what failure it might suggest. They only offered the suction leak likelyhood and told me to concentrate on the intake strainer and o-ring fitting on the suction intake of their pump. BTW, the 120V pump cuts in at around 45psi and cuts off at around 60psi. The 24V pump operates at 20/40psi. It does not matter if I leave the 24v pump on or turn it off after the initial pressurization of the system, it never comes on again and the 120V system works perfect every time. It is not like me to leave something in place that is not working perfectly and/or with a half assed solution but this system is a major PITA to access and work on so I am just enjoying the shower volume and pressure for now and am off working on more pressing problems.

There will probably never be another boat owner who will benefit from this "fix" in the entire future of the known universe but hey, everyone seems to have at least one twin out there so maybe this will help my water system twin some day.

 

[ADaily3224]

You may want to check the pressure in your expansion tank. The older tanks have a rubber bladder which should be pumped up to 3 lb psi. There's a tire valve on the top of the tank. If when you let the air out you get some water it's time for a new tank. The new tanks are plastic and much smaller. The newest pumps don't need a tank. They automatically spence demand and increase automatically. My tank is light blue.

Tony D