Integral metal water tank

[Melita]

I know that I'm going to have to take the top off and clean it out, but I can't understand why I can't get any water to flow.

 

So, on my 1980's refurb the water tank is under the well deck. The water inlet appears to come from very near the top. I've just finished the cold water plumbing and want to test it. I've put water into the tank, don't know how much, but the hosepipe was on for about 20 minutes. Turn the stop cock and there's nothing flowing, also, the pump will not suck any water in.

 

Took the pump apart and used an air blower to force air back into the tank, water then flows, but only for a couple of seconds - but this is only if I've replaced the filler cap. It appears that my air blower is pressurising the tank and then that is what causes to water to flow, but only 'till the pressure has gone.

 

Any thoughts or ideas? Could it be that there is a siphon pipe in the tank and this will only prime if the tank is full? It's obviously not blocked.

 

Thanks for any advice, Kevin

[David Mack]

Are you sure the pipe at the top is the connection for the water system and not actually the vent pipe (to let air out of the tank when it is filled and back in as water is drawn off)? It would be more normal for the water outlet to be close to the bottom of the tank. If you can pressurise the tank via this connection by replacing the filler cap that would suggest you don't have any other vent pipe.

 

[gatekrash]

Rust blocking the inlet pipe from the tank I would guess. Lots of us have had that happen. We ended up getting ours cut off and replaced with a stainless inlet pipe.

When we looked at the pipe that was cut off it was solid with rust, we'd managed to get water flowing briefly by poking a large screwdriver down it but the rust flakes acted like a valve and soon ended up blocking it again.

 

We also blew air down it until we got bubbles in the tank, but it only helped very briefly before water was reduced to a trickle again.

[Melita]

2 minutes ago, David Mack said:

Are you sure the pipe at the top is the connection for the water system and not actually the vent pipe (to let air out of the tank when it is filled and back in as water is drawn off)? It would be more normal for the water outlet to be close to the bottom of the tank. If you can pressurise the tank via this connection by replacing the filler cap that would suggest you don't have any other vent pipe.

Exactly what I thought, but the pump and stopcock are both connected to this pipe, pic enclosed.

[Russ T]

43 minutes ago, gatekrash said:

Rust blocking the inlet pipe from the tank I would guess. Lots of us have had that happen. We ended up getting ours cut off and replaced with a stainless inlet pipe.

When we looked at the pipe that was cut off it was solid with rust, we'd managed to get water flowing briefly by poking a large screwdriver down it but the rust flakes acted like a valve and soon ended up blocking it again.

 

We also blew air down it until we got bubbles in the tank, but it only helped very briefly before water was reduced to a trickle again.

The other thing that can happen is that the isolation valve can stick, reducing/stopping the flow. The handle will turn, but the valve not shut/open.

 

Probably not the cause in this case, as water is flowing.

Edited April 3 by Rod Stewart

[jim mitchell]

If the tank has accumulated a lot of debris (rust etc) in the bottom, then it can block the pipe outlet,  blowing air back will create a small depression around the pipe entry but as soon as you restart pumping it will suck that debris back in and especially with  the exit near the top of the tank  the pump suction will not be sufficient to lift the 'slurry'.

[Melita]

Thanks for quick replies, as I said, I'm just going to have to bite the bullet and remove the top plate - as you can imagine, the bolts are well and truly rusted in!

[jonathanA]

You know that's a gate valve not a stop cock dont you ? Gate valves are notorious for failing and causing problems.  So it would be worth taking that off and checking it or replacing it whilst your at it.

 

I suspect your right and getting in there is the answer. Expect to be horrified by what you find..... 😅

[Gybe Ho]

5 minutes ago, jim mitchell said:

If the tank has accumulated a lot of debris (rust etc) in the bottom, then it can block the pipe outlet,  blowing air back will create a small depression around the pipe entry but as soon as you restart pumping it will suck that debris back in and especially with  the exit near the top of the tank  the pump suction will not be sufficient to lift the 'slurry'.

 

This description sounds familiar, I had an acute version of the same problem on my previous sailing yacht that had a black water holding tank fitted. Repeated uses of an air pump eventually cleared the tank, however I was surprised how a little sediment in the bottom of the tank would repeatedly reblock the drainage outlet as a self moulding softplug. Human Beings are fitted with a similar device.

 

I eventually cleared the tank using a length of flexible plastic curtain rail pushed down through the deck inspection/suction pipe, this was waggled around the bottom of the tank. The plumbing of a canal boat water tank is different and I doubt the same technique would work, so yup time to open up the inspection hatch and dig out the debris from the bottom of the water tank once the obvious explanations have been ruled out.

 

OP have you tried to operate the water pump with the filler cap left off?  

[Melita]

1 hour ago, Gybe Ho said:

OP have you tried to operate the water pump with the filler cap left off?  

I have, both off and on! With the filler cap off, I don't get any water when I blow into the pipe!

 

1 hour ago, jonathanA said:

You know that's a gate valve not a stop cock dont you ? Gate valves are notorious for failing and causing problems.  So it would be worth taking that off and checking it or replacing it whilst your at it.

I do, thanks. I'll be bringing all new fittings when I come back next week.

[MtB]

Just open that gate valve wide. If it's opening correctly you should be able to just poke a stick straight through it and into the tank.

 

My bet is you'll feel an obstruction with your stick four or five inches beyond the gate valve, where corrosion is fully blocking the mild steel pipe stub welded into the tank.

 

If you find a blockage, you might clear a way through it by hitting the end of your stick with a hammer or if not, swapping the stick for a long-enough drill. 

[IanD]

34 minutes ago, MtB said:

Just open that gate valve wide. If it's opening correctly you should be able to just poke a stick straight through it and into the tank.

 

My bet is you'll feel an obstruction with your stick four or five inches beyond the gate valve, where corrosion is fully blocking the mild steel pipe stub welded into the tank.

 

If you find a blockage, you might clear a way through it by hitting the end of your stick with a hammer or if not, swapping the stick for a long-enough drill. 

...or make a hole which then leaks... 😞 

[MtB]

1 minute ago, IanD said:

...or make a hole which then leaks... 😞 

 

 

Vanishingly unlikely, given the location of the pipe stub in the photo.

 

 

[jonathanA]

I'm not sure @MtB the op suggested the outlet is near the top of the tank so there could be a drop tube on the other side.

 

Eta maybe something flexible might get round the bend if there is one

Edited April 3 by jonathanA
Add a bit

[IanD]

1 minute ago, MtB said:

 

Vanishingly unlikely, given the location of the pipe stub in the photo.

 

Not likely but not impossible, if the pipe is blocked with rust which has thinned the walls to next to nothing in places and this then gets ripped off.

 

A blockage is bad, but a hole in rusty metal with a full tank of water behind it is worse... 😉 

[Ex Brummie]

My tank outlet is at the top of the tank, with a length of 15mm Hep2O through a bulkhead fitting wh.i cWh piicks up about 1 ft into the tank.The natural lie of the boat means that I do not  take water from the very base of the tank so avoiding debris. If the outlet of the tank is at the top, maybe it could be adapted to a similar arrangement thus avoiding a drop tube with a sharp bend.