Full Version: RO/DI & Low Water Pressure
Can it be too low? I'm getting 20PSI right now which is weird cause normally I get 60.
City water or well?
QUOTE (Mr. Fosi @ Oct 31 2009, 09:49 AM) 
City water or well?
City, reservoir system. (NYC)
It's possible. There could be a line break affecting you right now.
QUOTE (Mr. Fosi @ Oct 31 2009, 08:59 AM)
It's possible. There could be a line break affecting you right now.
Does it negatively effect the quality of water I'm creating?
Yes.
The membrane is designed to operate within a specific pressure range. I'm not sure what yours is. Do you have a pressure gage monitoring the membrane chamber or just the PSI at the tap?
Low pressure means lower rejection rate IIRC.
The membrane is designed to operate within a specific pressure range. I'm not sure what yours is. Do you have a pressure gage monitoring the membrane chamber or just the PSI at the tap?
Low pressure means lower rejection rate IIRC.
Do you have your water maker hooked up to a sink faucet? If so, where did you buy the adapter, and do they make different sizes?
QUOTE (BumbleBeeJBG @ Oct 31 2009, 08:46 AM)
Can it be too low? I'm getting 20PSI right now which is weird cause normally I get 60.
As Mr F said, too low and your membrane loses it's efficiency. A booster pump can rectify that.
Seems relevant: Pressure and RO systems link
Thanks! I am reading 1 on the TDS instead of the 0 I usually do. We'll see if it's a prolonged problem.
You are most likely getting a very low rejection rate from the membrane and are burning through DI resin to compensate... I would be checking my plumbing and making phone calls if my PSI was reading that low for more than a day or two.
Or invest in a booster.
If you only have 20 psi available the membrane is not working at all, its being treated by the DI and bypassing the RO membrane. It takes at least 30-40 psi to pass water through a membrane.
Where are you reading 20 psi? At the tap, on an inline gauge close to the membrane and downstream of the prefilter and carbon or??
If it on an inline gauge try temporarily removing the prefilter and carbon, for no more than a couple minutes maxcimum, and see what the pressure reads. You may have pluged or fouled filters, this is very very common with New Yorks high sediment loaded waters.
Where are you reading 20 psi? At the tap, on an inline gauge close to the membrane and downstream of the prefilter and carbon or??
If it on an inline gauge try temporarily removing the prefilter and carbon, for no more than a couple minutes maxcimum, and see what the pressure reads. You may have pluged or fouled filters, this is very very common with New Yorks high sediment loaded waters.
On the flip side. What is the maximum pressure you want when using a booster? I installed a booster because I was getting 36psi (inline before RO). With the booster I was getting 85psi and have since dialed it down to 60ish.
QUOTE (AZDesertRat @ Nov 5 2009, 07:18 PM)
If you only have 20 psi available the membrane is not working at all, its being treated by the DI and bypassing the RO membrane. It takes at least 30-40 psi to pass water through a membrane.
Where are you reading 20 psi? At the tap, on an inline gauge close to the membrane and downstream of the prefilter and carbon or??
If it on an inline gauge try temporarily removing the prefilter and carbon, for no more than a couple minutes maxcimum, and see what the pressure reads. You may have pluged or fouled filters, this is very very common with New Yorks high sediment loaded waters.
Where are you reading 20 psi? At the tap, on an inline gauge close to the membrane and downstream of the prefilter and carbon or??
If it on an inline gauge try temporarily removing the prefilter and carbon, for no more than a couple minutes maxcimum, and see what the pressure reads. You may have pluged or fouled filters, this is very very common with New Yorks high sediment loaded waters.
You know I always read 70 TDS on tap water, we have a lot of sediment?
The only limiting factor on pressure is the housings and fittings, the membrane is capable of continous operation at 250-300 psi easily.
Most housings should be designed for 125 psi working pressure if they are UPC approved.
I keep my booster in the 90 psi range and it works great. The higher the better when it comes to effluent water quality and GPD production.
75 GPD Dow Filmtec membranes are rated at 75 GPD at 77 degrees F water temperature and 50 psi available pressure at the membrane. GE, Applied and others say 65 psi to obtain their rated flows at 77 degrees.
Spectrapure has published an excellent document that walks you through calculating the actual performance of your own RO membrane. Note the sections talking about pressure and temperature and how they affect the output. Higher pressure can overcome colder water temps.
http://www.spectrapure.com/CALC-FORMULA.pdf
If you have 77 degree water, which like most of us you probably don't, you could expect 51 GPD out of a 75 GPD membrane. Boost that to 60 psi and now its 93 GPD, 70 psi is 110 GPD and 80 psi is a whopping 128 GPD, again assuming 77 degree water. Lower that temperature to 50 degrees F and the flows drop to 30 GPD at 36 psi, 54 GPD at 60 psi, 64 GPD at 70 psi and 75 GPD at 80 psi. So 80 psi would make up for a drop in temperature from 77 down to 50 and still get the rated 75 GPD. Boosting pressure is much safer than trying to blend or temper hot and cold water together, thats the quickest way to destroy a membrane there is.
A TDS meter does not register sediment and particulates. They are TSS or Total Suspended Solids which can be measured with a turbidimeter or particle counter. Totally different thing but just as bad and really worse since suspendeds can hinder disinfection in drinking water and support bacteria and virus growth. Thats why NY is paying such high daily fines to the EPA until their surface water treatment plants are in operation.
Most housings should be designed for 125 psi working pressure if they are UPC approved.
I keep my booster in the 90 psi range and it works great. The higher the better when it comes to effluent water quality and GPD production.
75 GPD Dow Filmtec membranes are rated at 75 GPD at 77 degrees F water temperature and 50 psi available pressure at the membrane. GE, Applied and others say 65 psi to obtain their rated flows at 77 degrees.
Spectrapure has published an excellent document that walks you through calculating the actual performance of your own RO membrane. Note the sections talking about pressure and temperature and how they affect the output. Higher pressure can overcome colder water temps.
http://www.spectrapure.com/CALC-FORMULA.pdf
If you have 77 degree water, which like most of us you probably don't, you could expect 51 GPD out of a 75 GPD membrane. Boost that to 60 psi and now its 93 GPD, 70 psi is 110 GPD and 80 psi is a whopping 128 GPD, again assuming 77 degree water. Lower that temperature to 50 degrees F and the flows drop to 30 GPD at 36 psi, 54 GPD at 60 psi, 64 GPD at 70 psi and 75 GPD at 80 psi. So 80 psi would make up for a drop in temperature from 77 down to 50 and still get the rated 75 GPD. Boosting pressure is much safer than trying to blend or temper hot and cold water together, thats the quickest way to destroy a membrane there is.
A TDS meter does not register sediment and particulates. They are TSS or Total Suspended Solids which can be measured with a turbidimeter or particle counter. Totally different thing but just as bad and really worse since suspendeds can hinder disinfection in drinking water and support bacteria and virus growth. Thats why NY is paying such high daily fines to the EPA until their surface water treatment plants are in operation.
NYC has a lot of silt in the water because of the nature of the system. This doesn't register on TDS meters, as AZD said, but it will clog carbon or other media that sits in front of the RO membrane.
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