[Simon Carter]

I need up to 2000 litres a day. I've been climbing the walls as I could spit in the tank & fill it more quickly. Plus my ratio of pure to waste is diabolical. Not funny when you are on  a meter.
I think I have identified my problem, but would appreciate any comments. I'm on a small industrial developement/ex farm. The water pressure is ok, but Severn Trent were here yesterday & they said excessive demand is severely undermining flow rate to about 10 lites per minute. When others are using water, especially a guy who pressure washes vehicles round the corner, my pressuer gauge drops off even more.
Actually the pressure sometimes doesn't read too bad, but I understand both pressuer & flow matter. Apparently 15 litres per minute is necessary minimum.
My solution & my main question is a holding tank with a pump to feed the RO's, but if the tank is filling at 10 litres per minute & I'm drawing at 15, then I'm no better off surely?. The only other answer is my own mains connection, but that would cost thousands.

[drew86]

I have a similar problem, started processing water this morning pressure 55psi just been to shed to check progress and preesure down to 25psi, only getting a trickle of pure water, was getting 1:1 ratio but now looks like 2:1 in favour of waste, probably will have to get a booster pump.
                                   Drew.

[abacus]

Hi all
try www.derwentwatersystems.co.uk

they make a skid mounted s/s system with pressure pump
or you can even get 12 v prussure pump that have a small tank it improves flow and evens it out flojet make one others on the market too.

regards grant

[carl clearview]

Hi Simon,

Water pressure is the key here and PSI is far more important than flow rates for reverse osmosis water production. This example may help you understand the difference.
 
If you were to have a garden hose and placed your thumb over the end of it, you would stop the flow. The pressure would then build up behind your thumb. If you have a low pressure feed, you would be able to stop the flow indefinately, however, if the feed water has a high PSi you would not be able to stop the flow for long.

It would not matter if the high pressure feed had a lower flow rate, it would still have more pressure than the high flow rate and this is vital for use with R/O, bear with me and i'll explain why.

Osmosis occurs when two different concentrations of liquid (or solute) are seperated by a semi permeable membrane. The solute will always flow from the lower concentration solute to the high concentration of solute. In other words, the cleaner water, or solute, will dilute the more contaminated water. As the water passes through the membrane to the side which has a high concentration of particles, the liquid level raises, this is called OSMOTIC PRESSURE.

In order to reverse the osmosis effect we increase the HYDROSTATIC PRESSURE. The osmosis effect stops when the hydrostatic pressure is the same as the osmotic pressure, as our goal is to reverse the osmosis, we need to increase the hydrostatic pressure to a greater PSI rating than that of the osmotic pressure. The higher the concentration of particles in the feed supply, the higher the hydrostatic pressure needs to be to overcome the osmotic pressure.

The above rules show that if we want high permeate production rates from our R/O units, we have to increase the water pressure.
This is why flow rates are not as important as high PSI.

The recovery rate of an R/O unit should be set at around 75% permeate with 25% reject concentrate. It is important however, to choose the membrane very carefully, there are well over 300 different models from various manufacturers all with specific purposes and parameters. Your supplier should be able to help with that. If you need more infomation, fill out the 'contact  us' page on our website www.concept2o.com and i'll help if i can.

All the best,

Regards,

Carl phillips,
Clearview Plus Ltd.