Question:
Can anyone help with this? I need to store filtered water from an RO(Reverse Osmosis) unit and have the supply turned on and off as the tankfills and empties.

I have fitted a brass high pressure ball valve to my RO storage tank in theloft - same arrangement as in header tanks or WC cisterns. The mains supplygoes into the ball valve as usual and the RO input is screwed into the ballvalves output. The RO output feeds into the storage tank. In theory thesupply to the RO should cut off when the tahk is full.

As the RO output fills up the tank the float ball rises and starts to shutoff the supply to the RO unit. So far so good. When the supply is nearlyshut off the arm and float ball sink thus opening up the supply. From thispoint the supply (understandably) never shuts off.

Can anyone explain what's happening. It's like the pressure builds up andforces the float back down. The ball valve was from B&Q (Plumbfit 1/2 Pt 2(S/E H/P)). I've tried bending the arm to increase the pressure from thefloat but made no difference.

Answer: I do also and have an RO unit so perhaps I can add something.

First of all, your arrangement for hooking up the RO unit seems a bit odd -i.e. with the control on the input side of theRO unit. Is this a recommendation/requirement from the manufacturers?

Mine has a clamp and sting type of device which clamps onto a mains pressurewater pipe and would provide a continuous flow.It hooks up via 1/4" plastic tube to the RO unit via carbon and prefiltersand then to the membrane chamber.The output side is connected again via plastic tube to a pressure vesselwith diaphragm as the storage. There is a pressure switch which turns offthe flow through the unit when the back pressure from the store gets closeto mains pressure.Then there is a drain of course. The point is that the output side, not theinput side is controlled.

For storing larger volumes than the typical few litres of the pressurevessels from the manufacturers I have used a plastic storage tank but used aspecial miniature float valve intended for the application. The valve takesthe 1/4" tube and has entirely plasticparts apart from the pin which is stainless steel. This connects to theoutput side of the RO unit together with the pressure vessel and works verywell. I bought the valve from a marine supply place in the U.S. somewhile ago but could probably dig out the details if I looked.

Another point is the use of metals. You mentioned that you bent the arm onyour ball valve. Presumably this means thatit is metal (brass?). Many metals, especially copper and brass, arehighly toxic to marine invertebrates. Considering that this is fresh waterat this point it's probably not too much of a problem, but if you're goingto stick with your current arrangement then an all plastic valve would besafer.