12volt Pump conundrum

[Imintheshed]

Hi all,
I have three 1000litre IBCs that collect rainwater for use in our two toilets.

The upstairs loo is supplied via a 40psi 12volt pressurised pump ie it cuts off when the cistern is full (power comes from a solar panel feeding a second hand deep cell battery from a local Plymouth supplier for a tenner......bargain!).

The downstairs loo was gravity fed but, because it takes 20mins to fill (and 'cos I just can't leave stuff alone), I've just re-plumbed the hep2O so that both loos are fed via the pump.

And so the problems begin!

The pump sounds majorly unhappy when it feeds the downstairs loo......so much so that it has just blown a pressure switch....aaaaggghh!

The cisterns are identical, so it isnt a 'design thing'.

There are no blockages in the pipework.....the pump quite happily pushes water through all the way up to the connection to the toilet itself.

I just can't figure it out. Any ideas anyone?

Hopeful of Plymouth!

[Alan]

Quote "The pump sounds majorly unhappy when it feeds the downstairs loo......so much so that it has just blown a pressure switch....aaaaggghh! "

Is it just a bit of pipe work with a gentle rise and fall. Air gets trapped in the highest point of the pipe and is causing the pipe noise. ?

One would presume that the pressure switch is at ground level near the pump. ?
Toilet is flushed.
Ball valve in toilet system opens.
Pressure in the pumped system drops.
Pressure switch detects pressure loss and starts the pump.
Toilet system fills.
One or ten toilets, the system will work the same. Your 40 pounds per square inch should pump water to 92.25 feet.

If the system is as above it would not cause the pressure switch to fail.
What sort of pump is it. Diaphragm pump. ? Gear pump ?
Have you got a pressure gauge on the system. What is the pressure with the pump shut down ?

Regards

Alan

[Imintheshed]

Hi Alan,
Thanks very much for the quick reply.

Definately not an airlock - The pipework between the pump and the downstairs loo is 30ft of hep20 with a few L's and Ts (where the mains can be connected if required) and I have tested this (successfully!) using the pump right up to the point that the pipe enters the cistern. In any case, it was the pump itself that was struggling.....it was making a sort of ticking noise, still pumping the water but was clearly not happy doing so!

There is no pressure gauge on the system, but as soon as I tried the upstairs loo (with a replacement pressure switch), it worked perfectly.

Its a 12v self priming marine pump (with diaphram) from these guys http://www.galeforcemarine.com/pumps.asp and has an integral pressure switch.

The downstairs loo works perfectly when reconnected to the mains.

Mystery eh?

[Iain]

Hi
As the downstairs cistern was gravity fed, does it have the low pressure insert fitted to the float valve, might need a high pressure one. I had to go the other way with mine as mine are now fed with gravity rainwater (3 foot head). Had to remove the HP insert and put in a low pressure one (even drilled it out a bit to get a bit more flow)
worth a check
Iain

[pontiff]

Hi Alan,
Thanks very much for the quick reply.

Definately not an airlock - The pipework between the pump and the downstairs loo is 30ft of hep20 with a few L's and Ts (where the mains can be connected if required) and I have tested this (successfully!) using the pump right up to the point that the pipe enters the cistern. In any case, it was the pump itself that was struggling.....it was making a sort of ticking noise, still pumping the water but was clearly not happy doing so!

There is no pressure gauge on the system, but as soon as I tried the upstairs loo (with a replacement pressure switch), it worked perfectly.

Its a 12v self priming marine pump (with diaphram) from these guys http://www.galeforcemarine.com/pumps.asp and has an integral pressure switch.

The downstairs loo works perfectly when reconnected to the mains.

Mystery eh?

I've had almost the same issue with the pressure switch on one of these pumps. Got a replacement switch but still can't get it to work with my two toilets. The pressure switch didn't seem to switch off the pump and and blew out a push fit elbow and water started pouring out of the other end of the pump ( opposite end to the pressure switch.) The 20A fuse blew too! Have gone back to my less powerful shurflo which works perfectly. The toilet valves are Fluidmaster compacts.
Pity, as the pump itself is very powerful! Hope you can figure out what the problem is but I fear it's the pressure switch design.

[Justme]

Do you have an expansion / pressure vessel in the system?

If not you are relying on the elasticity of the poly pipe to hold the pressure rise to trip the switch hence the blown joint. With a vessel you can have a lower pressure trip & take the strain off the pump.

[clivejo]

Could it be a leaky value?  Or something stuck in it?  

I once had a ball value that sounded like a cat being killed very painfully! The screams sent a shiver down ones back!

[Baz]

Because the lower loo does not actually need pressure ( gravity would work) the pump is not working against enough resistance so is running faster than it likes. As the flow gets going after the diaphram is depresessed ( too easily because it is low pressure) the motor tries to pull it up, sucking in water, but the momentum of the outflow is pulling water out so the motor has to work hard on the upstroke. So the pump big and little end bearings are straining in the opposite direction to their design.
When the float valve shuts off the water it is a bit sudden, the momentum of the water coulmn is converted into a pressure pulse that whacks the pressure valve.
The solution is to fit a gate valve in the pipe and close it, shutting off the pressure switch. Then open it slowly allowing just enough flow to fill the cistern while keeping the pump happy working against the pressure.

[pontiff]

Some great suggestions here, I'm going to try a bigger expansion vessel and a gate valve. Thanks for the info.

[Baz]

found the missin'  'g' - it fell on the floor  

for the record, which pump are you using - if the problem gets solved would it be recommended?