RODI and low water pressure.

[chrisdaphish]

what happens if an rodi is used without the proper water pressure? my unit is producing very little water, and hter eisnt much waste water coming out.. I get maybe 3 gallons every 4 hours, so tehre is something wrong... It is reading 000 tds tho. Anyways what woudl cause this ? low water pressure? and IIRC low water pressure is bad for the rodi, but how bad and why is it bad? What can i do to increase the water pressure(find a new sink in teh house?)
TIA

 

[trillyen]

well I would say it was a plumbing issue just turn up the water pressure on that sink

I would look up under the sink or the the house for the valve but low pressure is better than to much pressure

Always make sure the water is cold also cause hot water could ruin the membrane

 

[DonW]

Low pressure is going to cause low output. This time of year everyones output takes a hit due to low water temps. 0 tds after the di is not a good judge. Check you incomming and output after the membrane before the di. This will tell you what your membrane is doing and wether or not you damaging it.

Don

 

[mmkeeper]

If low pressure is a regular problem, there are in line pumps you can buy for your filter.

 

[mcvicker]

Okay this may be a dumb question followed by a suggestion based on my experience. Don't the RO/DI machines have a regulator that provides the proper back pressure, right? So, shouldn't back pressure be fairly constant? I know that isn't the case because I have low pressure too and my RO/DI outlet was low. I changed the first filter from a low micron sedimentary filter to a home depot carbon filter and suddenly my RO/DI output increased. It doesn't seem to me like you need the super low micron on the front, just enough to protect the membrane from damage.
-chris

 

[Herefishyfishy]

The membrane is the valuable part, protect it. There is no regulator other than the restricter at the start of the waste water line. If you have low water pressure, filter changes will not help, you need to add a booster pump.

 

[DonW]

Okay this may be a dumb question followed by a suggestion based on my experience. Don't the RO/DI machines have a regulator that provides the proper back pressure, right? So, shouldn't back pressure be fairly constant? I know that isn't the case because I have low pressure too and my RO/DI outlet was low. I changed the first filter from a low micron sedimentary filter to a home depot carbon filter and suddenly my RO/DI output increased. It doesn't seem to me like you need the super low micron on the front, just enough to protect the membrane from damage.
-chris

Sort of but there is low flow and low pressure both will cause low output. Low pressure is low house line pressure. Low flow is usually plugged sediment filters. The easiest way to diagnose rodi problems is with a cheap pressure gauge or two and a tds meter.

Don

 

[mcvicker]

I want to clarify that the best recommendation is to either move the RO-DI unit to a faucet with higher pressure or purchase a booster pump. I would check the first sediment filters and change more often. If you don't want to risk the membrane with the carbon filter you can switch to a pleated absolute style filter (like an accordian http://www.home-water-purifiers-and-filters.com/pentek-r.php ) instead of a "depth filter (
http://www.home-water-purifiers-and-filters.com/pentek-polydepth.php). The pressure drop across those are usually lower, if you go to home depot they generally have both the pictures are just something I googled quickly as pictures of the two styles. Most likely if you have low water pressure you have iron pipes and the first filter clogs up quickly so you should change the sediment filter more often.

For my own education (from those with more experience on RO/DI):
If you had a pressure gauge could you modify the restrictor on the waste line to raise the pressure at the membrane to the design pressure? I imagine this would lower the membrane life due to lower flow across the membrane. What pressure are the membranes designed to run at?
-chris

 

[DonW]

Water flow has nothing to do with water pressure. I dont understand "risk the membrane with the carbon filter". Your risking damage to the membrane if you dont use a carbon filter. The carbon removes chloramines that destroy the membrane. Modifying the flow restrictor will not effect pressure it will just ruin a perfectly good flow restrictor.

Don

 

[apollothesun]

when's the last time you changed the filter? i have a whirlpool version and i have to change the first stage filter every 2 months. i write the date on the filter to reference. also, i added a pressure gauge at the end of my ro/di and when i notice a drop in pressure that means i need to change the filter. good luck

 

[mcvicker]

Bernoulli established that water pressure and flow are directly proportional. All I am trying to state is if the incoming pressure is 60 pounds and your initial filter has a 30 pound drop then you could increase output by purchasing a filter with a 10 pound drop across it. Different brands of filters publish their pressure drops versus flow rates and they are variable (sometimes highly). Generally there is a sediment filter, a carbon filter, the membrane, then a DI filter. If you replace the initial sediment filter with a household "prefilter" that has a 5 pound pressure drop you can increase the pressure at the membrane by 10 pounds.

My question regarding the restrictor is it is designed for new homes with a high input water pressure to maintain a back pressure on the membrane to drive the osmotic process. If your incoming pressure is lower you can raise the back pressure with a different designed restrictor.

 

[burning2nd]

HEY IF it makes you feel any better... i left my flush valve on for a night and a half....

yep....

geting that new Ro soon

 

[Scooterman]

My question regarding the restrictor is it is designed for new homes with a high input water pressure to maintain a back pressure on the membrane to drive the osmotic process. If your incoming pressure is lower you can raise the back pressure with a different designed restrictor.

Some older flow controls are adjustable to tune your output per-say but the normal restrictors are designed to work with the designed membrane & is usually stated on the membrane. Most RO/DI units will recommend an incoming pressure from 60psi to 90psi, higher being better performance to waste. My house provides 89psi on the input, using a gauge like Don mentioned is almost crucial to getting the most out of your unit & determining when filters may need to be replaced, along with a TDS meter. If you have lower incoming pressure they usually recommend a pump to increase the water pressure.