Water pump on a flexible water tank

[kevsbox]

Hi
My yacht came with a flexible water tank fitted to a foot pump at both sinks. I have now added Rule 12v pump and powered tap to the wash sink but then we operate it no water is forthcoming.
We can here the pump turning but the tap is dry. I then tested the pump by disconnecting from the tank and dropping into a bucket of clean water. When I operate the tap here all works well.
So is this a pressure thing with the flexible tanks? or do I simply need a stronger pump.
I am not sure of the size and make of the flexible tank, it was there when I purchased the yacht but it is similar to the plastimo flexible tanks.
Any thoughts please.
Kev

 

[Bodach na mara]

There should be no problem with such an arrangement. That is what I have on Sea Hawk and had on a previous boat. By "flexible tank" I assume you mean a big rubberised or plastic bag.

 

[duncan99210]

Is the Rule pump self priming? If it’s a centrifugal pump, it won’t be able to suck the air out of the pipe, you need a diaphragm pump to do that.

 

[penberth3]

Is the Rule pump self priming? If it’s a centrifugal pump, it won’t be able to suck the air out of the pipe,......

But it will be Ok if the inlet is always below water level. No idea of the OP's arrangement.

 

[pvb]

Reading between the lines, I think the OP has got one of those little centrifugal pumps, connected to a tap with a microswitch in it. It will only work if it's mounted below the water level in the tank - it won't self-prime. And running it dry will damage it. I'm guessing the pump is something like this...

 

[duncan99210]

If it’s one of those pumps, it won’t prime even if it’s below the level of the tank if the air in the pipes isn’t removed. Really need a diaphragm pump which will self prime properly.

 

[pvb]

If it’s one of those pumps, it won’t prime even if it’s below the level of the tank if the air in the pipes isn’t removed. Really need a diaphragm pump which will self prime properly.

If it's below the level of the water in the tank, and if the tap is open, water should flow into the pump and prime it.

 

[duncan99210]

If it's below the level of the water in the tank, and if the tap is open, water should flow into the pump and prime it.

Oh that this would work. I fitted a pillow tank and centrifugal pump linked to a switched tap. The tank was higher than the pump, the pipe was on the bottom of the tank so thought I, well it’ll work. And it did provided you sucked the water through the pipe to start with. Any air in the system at all and it would refuse to prime. Dumped the centrifugal pump for a hand pump for that season then replaced it with a small diaphragm pump over the next winter. Really a much better solution, albeit more expensive then as the infinite variety of eBay water pumps weren’t available then.

 

[kevsbox]

There should be no problem with such an arrangement. That is what I have on Sea Hawk and had on a previous boat. By "flexible tank" I assume you mean a big rubberised or plastic bag.

That is correct

 

[kevsbox]

Thanks all, the pump is not self priming and so that would appear to be the problem. The pump is not well placed, will sort that out at the weekend.

 

[Boater Sam]

AS a rule,,,,, these don't work as water pumps any further than you can spit.

 

[kevsbox]

AS a rule,,,,, these don't work as water pumps any further than you can spit.

Getting that impression

 

[alahol2]

I used one of these (or equivalent) for a few years. What I found was that, although it was at the lowest level of the water pipework, it seemed to prefer to draw water, not from the tank, but from the heads branch of the water pipe. Solved by putting a non-return valve on the heads branch. It could still be temperamental at times when water in the tank was running low.
I've now got a decent sized diaphragm pump that always works.