Fresh water system - multiple tanks

[Shona]

Hi I’m new here but have read many forums from this website that have helped me resolve other issues. You all seem to be a wealth of knowledge.

Unfortunately I haven’t found a solution for my current problem so I’m putting it out there.

We have multiple (4) fresh water tanks on board and they meet at a common junction point before going through the water pressure pump and to the fixtures and fittings.

Three of the four tanks work very well so that makes me believe it’s not a pump problem, however when I switch to the fourth tank (bow tank) the pump takes a really long time to prime and switch off and when I use the breather pipe it spits and squirts like there’s air getting in somehow.

We have tried multiple problem solving ideas
- checked the pipe for leaks
- checked the tank for leaks
- checked connections and replaced just in case
- blown through the pipe to eliminate any blockage issues
- checked tank breather

I was thinking next thing would be replacing the pipe from tank to junction or are then any other suggestions?

Thanks

[GordMay]

Greetings and welcome aboard the CF, Shona.

[JoeRobertJr]

Originally Posted by Shona

Three of the four tanks work very well so that makes me believe it’s not a pump problem, however when I switch to the fourth tank (bow tank) the pump takes a really long time to prime and switch off and when I use the breather pipe it spits and squirts like there’s air getting in somehow.

Hi, Shona,
Questions:
After you switch to the fourth tank, and after the long prime and the pump has switched off -- later, when you use water, does the system also take longer than normal to repressurize and turn off? Or does it behave normally after the initial difficult priming?
Could you clarify "use the breather pipe"? Do you mean using a faucet downstream of the pump? Or are you doing something with the tank vent line, the line that lets air into tank while the pump is pulling water out?

Sputtering at a faucet would certainly suggest sucking air somewhere along the supply from the fourth tank, especially if it happens all the time while using the fourth tank.

[sailorboy1]

My water system always spits air a spurts after switching tanks a while till the air gets back out of the system. Unless the tanks were higher than the pump i would feel that is normal.

[Smokeys Kitchen]

Originally Posted by sailorboy1

My water system always spits air a spurts after switching tanks a while till the air gets back out of the system. Unless the tanks were higher than the pump i would feel that is normal.

+1

I have 3 tanks linked together on a manifold. I switch over when one goes empty and both the foot pedal and pressure pump gurggle and spit until the air is purged.

I do switch off the empty tanks though, since otherwise I would just be pulling pump into the air

[roland stockham]

As Sailorboy 1 says if either the tank is lower than or part of the pipe runs uphill you can have issues with air locks. I would expect that once they system is primed it would then run OK if this is the issue. The fact that it is the bow tank (therefore the longest pipe run) makes this the most likely one to air lock. You don't say what size the boat is but it is possible on a large boat that it could simply be that you are close to the priming limit on the pump. All pumps have a max prime expressed in feet of head but it is actually just resistance. If the pump is pulling fluid through a long narrow pipe it could be near it limit even with little rise.

A possible solution and improvement to the boat may be to fit a hand pump that taps in before the pressure pump but. You may need a maniflod with shut off valves at the junction to do this. This would enable you to hand prime the system and also draw water in the event of an electrical failure.

[Mark Thurlow]

Do you have 4 filling points ie one for each tank.

If yes or even if you have 2- open all tank fillers and all manifolds to allow free flow of both water and trapped air. Fill all tanks to overflowing in rotation.

This will prove all tanks are filling and air is being expelled.

I had similar issues and eventually only way to prove tanks were being filled to capacity was to drain all and then used a pre-timed flow rate -(into a jerrycan) to test forblockages.

[Mike Banks]

I would never have the pipes meet at a simple common point, but I would have an inlet manifold to the pressure pump, with individual ball valves from each tank, and a particulate filter on each tank feed to the manifold, (use irrigation filters--cheap as chips and very effective in preventing pump damage) and I would have each tank separately vented through insect-proof filters. I make mine using irrigation filters packed with soap-less stainless steel kitchen pot scouring pads in addition to the perforated plastic sieve already inside them. Air gets in or out but nothing else has a chance.

If your bow tank seems obstructed it probably is. To find out, I would use a temporary garden hose laid through the boat to the tank and connected to the pump inlet manifold. If that apparently fixes the problem, then you know the problem is somewhere below in the original water feed, and probably a blocked filter hidden somewhere, or a squashed pipe. Sometimes the whole thing has to be removed and replaced.

Another thought. My bow tank was not used for drinking water, it was a black water holding tank. It had its own deck outlets and carbon filter systems, and in your case may have been what the designers of your vessel had in mind when they put it there. The bow is the best place for such a tank. The more pronounced motion of the vessel at the bow keeps the macerated contents from settling into a difficult to remove solidified mass, and the baffling used in such a tank is less and does not extend fully to the base of the tank, being only to prevent excessive surface movements of the sludgy contents..

[Shrew]

Why switch from tank to tank? I need to draw from both of my tanks evenly, or else, I'll develop a list. Is it possible to simply leave all the tanks open and draw from each equally?

[Grattaway]

Shona hi
One possible solution depending upon heights is to allow the bow tank to gravity feed into one of the other closer tanks rather than to the pump. that way its a shorter line for the pump for priming and you know they work
Wayne

[Mike Banks]

Yes. I keep mine separate, even if all valves are open, because if one develops a leak it can be drained by closing off the others and using its contents firstly, then switching to the other tank or tanks while it is repaired.

[Shona]

Okay so currently more questions than answers. But here goes...

Our yacht is a 51ft mono. The four tanks one at the bow, 2 at mid ships and one aft. They all enter a manifold (just didn’t know the terminology earlier) and we usually rotate the filling any using of the tanks with the valve switches on the manifold. The breather pipe I was referring to is essentially a tap with a bit of hose into a bucket after the pump to let out any air when switching tanks.

All tanks were all previously working fine so all the advice in regard to being too far away to prime or gravity etc would be null and void.

Over the last few days we have tried and tested loads of things:

Emptied the water tank, thoroughly inspected it and decided it was fine, no cracks or leaks. Put that all back and filled the tank.

We ran the garden hose from in the tank straight to the manifold and it worked so we figured we’d replace the whole length of water pipe - did that - didn’t work.

Tried changing it to a different position on the manifold - didn’t work.

Cleaned out and changed O-ring on the pre-filter.

Tried putting the new water pipe straight into the tank - this worked so we thought maybe the uptake pipe could be blocked.

Took the uptake pipe off and it was clear and clean. Reattached and tried again, still not working.

Could be the connector from pipe to intake - switched it for one on another tank that we know is working. Still didn’t fix it.

So we are stumped. We feel that because it primes and works by putting the water pipe directly into the tank that it must be either the uptake pipe or hose connector but after inspecting both we’re really at our wits end...

Anyone think of anything else?

[Lepke]

If you use a tank manifold, you can use the tanks to correct any list. I have 4-100 gallon tanks in a row from port to st'bd. and move water to correct any list or make up for empty fuel tanks.

[Mike Banks]

For water to come out of a tank, air has to go in or eventually either the water stops or the tank cracks or collapses under atmospheric pressure. Each tank should have an individual breather pipe at the top of the tank, so that it not only provides a breather for excess pressure to vent, but to allow air to come in as the water level falls.

One can not just have ONE breather, but one can have one filtered air inlet/outlet with a separate breather run from it to each tank. I find it easier to vent each tank closely to the tank itself where possible--but sometimes one simply has to have a remote or close-by breather to each tank. Each tank must have originally had one--but they may be hidden and blocked by insects or debris.

There is another possibility--but it is an unlikely one. Some pipe fittings incorporate a one-way safety valve. If they are fitted the wrong way around--no water can reach the pump.

[JoeRobertJr]

Shona,
Your troubleshooting strategy has been very systematic, and I agree is sounds like you have isolated the problem to the uptake at the tank.

Just to confirm one point: when you had the suction hose stuck directly into the tank, you did this through an access port. When you moved the suction hose back to the normal uptake connection, and the problem returned, did you leave the access port open? That would eliminate any concerns about the tank's vent line being blocked.

Focusing on the uptake:
- You already inspected the uptake and the connection fitting, but I would double-check these for a crack that lets air in.
- Ditto on Mike B's suggestion to confirm there is not a faulty check valve in the uptake.
- Depending on the type of fittings, it could be difficult to get an air-tight seal. I had a fitting on a pump supply line that was sucking air until I pressed plumber's putty around the seam. The putty was just a temporary troubleshooting step to confirm where the air was getting in.

Happy hunting!