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Low water flow RO filters - Tank Pressure Problem
Last Updated: 03/10/2020
The number one reason for low water flow from a reverse osmosis system is low air pressure in the holding tank.

The Problem: Low Volume and Poor Pressure
Little to No air pressure will result in very little water being pushed out of the holding tank. You will have a full and heavy holding tank, but with out the air pressure, you'll never get much water out of the tank. Too much air pressure ( say over 10 psi on a small tank ) will result in good water flow but will severely limit the amount of water that can be stored in the holding tank. So, it is recommended to put 8 psi of air in your under the sink reverse osmosis holding tank. If you get water coming out of the air valve, then it is time to purchase a new holding tank.

To Check:
With all possible water drained from the holding tank, you want to get an air pressure reading of 8 PSI of air pressure. There is a "tire" valve on your holding tank somewhere ( usually the bottom ). You really should use a special low pressure air gauge.
One that shows the air pressure in one pound increments starting with one pound. The average tire gauge starts at 5 or 10 lbs. psi.

One method ( see Video links below for others ) to get the WATER out of Water Logged Tank ( and be able to check true "air pressure" ),
I usually open the RO faucet ( with RO inlet water turned off, but TANK still ON / OPEN ),
and add compressed air to the air valve on the tank. Still under the sink, and very heavy at this point.
Just a little air pressure at a time until all water comes out ( can take 10 - 20 minutes of slowly adding more air ).
DO NOT Over pressurize the tank.
Air pressure above 10 psi can rupture it internally.

If tank does EMPTY of all water, and holds 8 psi of Air pressure, you can turn the Incoming water Back On.. allow 6 - 12 hours for tank to Refill with water.

If the tank will not hold air pressure, or if water comes out the air valve stem, then the tank ( RO Storage Tank ) will need to be replaced with a new one.
See:Replacement RO Tank

To see how > Youtube Video about Adding Air to Tank

Or this longer version where you actually see the water being pumped out of the storage tank that is low on air pressure,

Refill RO storage Tank time question:
**** If your Membrane is 50 gpd ( gallons per day ) then it makes about 1 - 2 gallons of water per hour....
It's rated to make 2 gallons per hour, but that is only if your water pressure is at least 60 psi, and the water temperature is at least 77 degrees.
Less pressure or lower temperature will slow the production rate of the membrane.

So, give the unit 3 - 6 hours to refill and shut off.

And if you have an older 25 gpd TFC or 14 gpd CTA membrane expect it to take a lot long to fill an Empty Tank, before the system will "shut off" and stop making water.

QUESTION - and Possible Causes for Low Output,

I pressurized my tank (it was very low) and have installed the new 50GPD membrane and still have low output. So is a new tank next? Do old tanks just “wear out” like we do when we get old? (Don’t know your age, but I know I am at that age).
OLD tanks can rupture internally, and Not hold the air pressure needed to "push out" the water stored in the tank.

** Did you have the tank water valve OPEN while ADDING air pressure to the holding tank?
You need to "push out" ALL the water in the tank, and then continue to add air pressure until you have about 8 psi at the air valve.

Low "output" is due to one of the following:

1 ) Low incoming water pressure from water source
a ) increase water pressure if possible
b ) Check that your "tap" or "shut off" that "FEEDS" the RO is not partially clogged. I've seen this mostly we older models that using a "Piercing Valve".
c ) The Pre-Filter is clogged, and needs to be replaced.

2 ) RO storage tank does not have enough "air pressure" ( ideal is 8 psi .. no more, and really only starts to "fail" when less then 2 psi ).
*** If any water comes out the Air Valve, then the tank needs to be replaced.. adding Air will not work ( hold the air ).

3 ) Post filter clogged or in Backwards ( primarily applies to using using 4 or 5 stages, with the last stage an IN LINE GAC filter,
or with Microline systems,
this one:

4 ) Not enough Time has been allotted for the membrane to MAKE the water and FILL the tank.
New membranes and any older CTA membranes can require several days to be come fully saturated ( wet ) and reach full production rate.
NOTE: Production rate is very slow ( average 1 gallon per hour, but can be less ).
And the lower the water pressure or water temperature, the slower the membrane will be "making" pure water.
That is why there is a Storage Tank that is pressurized ( to provide a good flow of water when you need / want it ).

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