Reverse osmosis tank

[Taylorjm]

So I built my own RO filter setup with a vane pump and 400gpd membrane. Out of simplicity sake, I'm using a vane pump and an 80/100psi pressure switch to a 400gpd membrane and out to a small RO storage tank and a 40/60psi pressure switch on the output. I get about 5 gallons drawdown at 12psi and it feeds a refrigerator and side faucet on the kitchen sink with 1/4" id pex line. It takes about 30 min to fill the storage tank when empty, and the pump kicks on after using maybe a gallon of water when the tank drops to 40psi. I'm good with the water production rate, but wondered about the storage tank psi. I know ro tanks are usually low, 7-10psi range, but they are usually also low output pressure because they don't normally have a high incoming pressure. I tried setting the tank at 38 psi like a well bladder tank, but then my drawdown is much lower. I also have another smaller, maybe 3 gallon ro tank that I could put in series to give me some more storage, or I also have a leftover 20 gal well pressure tank that's in great shape because I just upgraded mine to a larger one. The 20 gal well pressure tank only has about 5 gal drawdown at 38 psi, so not sure what that would gain me since I now have 5 gal drawdown at 12psi. Since it's only going through a 1/4" pex line, I don't know if the higher pressure in the tank is needed. So what should my storage tank pressure be?

 

[Reach4]

RO tanks are set much lower precharge for the reasons you said. They are different kinds of tanks and really limp diaphragms. You can't use a well pressure tank for RO storage.

The general rule is don't run RO water through metal.

 

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[Taylorjm]

RO tanks are set much lower precharge for the reasons you said. They are different kinds of tanks and really limp diaphragms. You can't use a well pressure tank for RO storage.

The general rule is don't run RO water through metal.

Right, but aren't well pressure tanks also lined so the water doesn't come in contact with metal? At least the new amtrol one I put in is lined and I believe the tank I have left over is an ao smith. I know ro tanks are lined. So is the membrane with an ro tank different than a well pressure tank in the terms of "limpness". I'm actually running my water through a Calcite/Corosex PH Balancing Cartridge after the ro membrane and the ph went from about 6.5 to 8.0 so there shouldn't be any issues with coming in contact with metal. It also adds some hardness and minerals making it more alkaline. We definitely like the taste more than without the ph balancing cartridge.

 

[Reach4]

The pH-raising cartridge should protect metal.
I am surprised you like the taste of the straight RO water better than the remineralized version.

So I am certainly not expert on these tanks. Yes, there is lining, but he input elbow is metal. Is that some stainless that RO won't bother? I don't know.

But the diaphragms are very different in RO tanks. They are made to take a bigger range of pressures without excess stress I think.

 

[Taylorjm]

The pH-raising cartridge should protect metal.
I am surprised you like the taste of the straight RO water better than the remineralized version.

So I am certainly not expert on these tanks. Yes, there is lining, but he input elbow is metal. Is that some stainless that RO won't bother? I don't know.

But the diaphragms are very different in RO tanks. They are made to take a bigger range of pressures without excess stress I think.

Sounds good. Thanks! I may have worded it weird originally, but we do like the taste of the remineralized water better. I may just add another ro tank in series to this if I want to increase capacity. We will see this summer when the home gets used more. I'm thinking that 5 gallons of ro water that's just used for ice and drinking should be plenty especially when it can be replenished in 30 min.