Fresh water tank not working - why?

[alisdair4]

Earlier this year, I added a second (flexible, Plastimo) water tank to MD. The existing, main tank is also flexible, and also by Plastimo. The feed from the 2 tanks is switched by a gate valve. Fresh water is pumped both electrically and by a hand pump, to the galley and heads sinks

For some reason, which may be incredibly obvious - but not to me(!), fresh water draws off the main tank by both electrical and manual means. As soon as the valve is switched to draw from the second tank, I feel a back pressure on the hand pump, and the electric pump runs dry.

Can any forumite suggest a solution?

A simple diagram of the system is here: http://www.midnightdrifter.net/html/water_system.html

 

[VicS]

No diagram !

May be I am being dense but I don't see how you will change tanks by means of a single gate valve. Perhaps you don't mean gate valve!

You have some sort of change over valve and you have connected it incorrectly.

 

[sailorman]

Earlier this year, I added a second (flexible, Plastimo) water tank to MD. The existing, main tank is also flexible, and also by Plastimo. The feed from the 2 tanks is switched by a gate valve. Fresh water is pumped both electrically and by a hand pump, to the galley and heads sinks

For some reason, which may be incredibly obvious - but not to me(!), fresh water draws off the main tank by both electrical and manual means. As soon as the valve is switched to draw from the second tank, I feel a back pressure on the hand pump, and the electric pump runs dry.

Can any forumite suggest a solution?

A simple diagram of the system is here: http://www.midnightdrifter.net/html/water_system.html

Tank Breather ?????

 

[VicS]

Tank Breather ?????

Would not stop it working with flexible tanks... just collapse the tank!
(Pillow tanks don't have vents)

 

[MoodySabre]

It's not switching over - the suction from the pump and the hand-pump is on the empty tank. The 'back pressure' is a vacuum in the first tank. As Vic says - a gate valve will shut something off or open it up but not both. If it is a change over valve then perhaps it is back-to-front.

 

[theoldsalt]

Diagram not visable for me either.

Can you post a copy?

 

[nimbusgb]

if you have a switchover valve a,b,c with b the common leg you should have tanks connected to a and c so valve makes either ab or bc. If you have incorrectly connected the common takeoff to either a or c then it will work in one position, in the other it connects the tanks together and shuts off the common.

 

[alisdair4]

Switchover valve (sic)

I now see the risk of posting pretending a knowledge I don't have! I am unsure if "gate valve " is the correct term.. It is a two-way valve which takes a feed from two inputs and puts it into one. (in this case, the input to the water feed). There i no third option -it either draws from tank 1 or tank 2. I really don't think I have wired it up "ass-backwards" because when I disconnect the feed pipe from the forward (non-working) tank, water flows freely from the feed pipe from the tank. As for breathers - I didn't think they were necessary with collapsible tanks. I#ll try to refresh the link in the morning.

 

[alisdair4]

Water Tank (Refreshed Link)

I think this picture should work...http://www.facebook.com/photo.php?f...45771255.45807.176203555771564&type=1&theater

 

[Babylon]

Would not stop it working with flexible tanks... just collapse the tank!
(Pillow tanks don't have vents)

Mine do - and they still collapse when emptied, but that is simply due to the fact that 'deflated' skins collapse anyway.

 

[Thistle]

I now see the risk of posting pretending a knowledge I don't have! I am unsure if "gate valve " is the correct term.. It is a two-way valve which takes a feed from two inputs and puts it into one. (in this case, the input to the water feed). There i no third option -it either draws from tank 1 or tank 2. I really don't think I have wired it up "ass-backwards" because when I disconnect the feed pipe from the forward (non-working) tank, water flows freely from the feed pipe from the tank. As for breathers - I didn't think they were necessary with collapsible tanks. I#ll try to refresh the link in the morning.

Are you disconnecting at the tank side of the valve? If so, you are showing that a breather is unnecessary and that the problem lies with the valve (we know that the pipework etc downstream of the valve is OK.) I would check again that the valve has been put in the right way round.

 

[Hoolie]

... ... ... I would check again that the valve has been put in the right way round.

And check you have the valve handle in the right position. I have several c/o valves in our system and I always have to set them by trial and error as the orientation is not at all obvious. (the boat is French-built!)

 

[Bilgediver]

I now see the risk of posting pretending a knowledge I don't have! I am unsure if "gate valve " is the correct term.. It is a two-way valve which takes a feed from two inputs and puts it into one. (in this case, the input to the water feed). There i no third option -it either draws from tank 1 or tank 2. I really don't think I have wired it up "ass-backwards" because when I disconnect the feed pipe from the forward (non-working) tank, water flows freely from the feed pipe from the tank. As for breathers - I didn't think they were necessary with collapsible tanks. I#ll try to refresh the link in the morning.

Alisdair....You could well have the valve ass about tit as you tested by disconnecting the valve from the tank. The valve was downstream and so this no test of the valve. You sould disconnect the feed from the valve to the pump and then test with the valve in each position. I suspect in one position nothing happens.

I suspect you have one of the tank feeds switched with the pump suction.
in one position you are drawing from one tank and in the other position the tanks become interconnected and the suction blocked. It should be easy enough looking at the valve to realise which two connections need to be switched!

 

[VicS]

I think this picture should work...http://www.facebook.com/photo.php?f...45771255.45807.176203555771564&type=1&theater

Nothing wrong with what the diagram shows.

There can be little doubt that the valve is plumbed in incorrectly. Take it out and examine it. I'd expect the correct connections to be quite obvious!

Post some photos of it if you still have a problem

BTW a gate valve :

 

[alisdair4]

Back to front valves

Thanks for the picture of the Gate Valve, Vic - that is definitely not what I am referring to!

It sounds like the problem is with the orientation of the valve - I'll take it off and check when I am next on the boat.

Thanks for the help - at least I have had confirmation of some of my hypotheses..(and also that I am rubbish at plumbing- but I knew that!)

 

[sarabande]

perhaps it might be that the inlet from the second tank is blocked by a plug or similar in the leg of the Y valve leading to that tank ? Or a blockage in the pipe work ?

 

[wolf]

Flex tank

I have a similar problem with my single tank, some times the skin sucks over the outlet try blowing back up the pipe.