Franklin SubDrive 75 - Increasing Pressure

[Silly Rabbit]

The pressure gauge on my line is showing 40psi. The pressure at the taps is fine, but not strong. I have an RO system in my kitchen and it is recommended to have 40-60psi to to operate properly. I find that my 3 gallon RO tank is only providing me 1.5 gallons. It should have 2.2-2.5 gallon capacity and I think the 40psi supply pressure is the reason it doesn't. I just replaced the tank for this issue and got the same results.

I would like to increase the pressure. In the Franklin manual it says you can increase the water pressure by adjusting the pressure sensor. I understand how to do that. Do I also have to change the pressure in the tank? What pressure should an empty tank read at 50psi? 60psi?

 

[Valveman]

The pressure gauge on my line is showing 40psi. The pressure at the taps is fine, but not strong. I have an RO system in my kitchen and it is recommended to have 40-60psi to to operate properly. I find that my 3 gallon RO tank is only providing me 1.5 gallons. It should have 2.2-2.5 gallon capacity and I think the 40psi supply pressure is the reason it doesn't. I just replaced the tank for this issue and got the same results.

I would like to increase the pressure. In the Franklin manual it says you can increase the water pressure by adjusting the pressure sensor. I understand how to do that. Do I also have to change the pressure in the tank? What pressure should an empty tank read at 50psi? 60psi?

The manual should tell you that. But I think it is 75% of the air charge on that one.

 

[Sponsor]

 

[WY_WaterWellGuy]

The manual should tell you that. But I think it is 75% of the air charge on that one.

This ^^

I believe Franklin recommends the tank be charged to 70% of the system’s operating pressure. So if you set the sensor to 60 psi, you should air the tank up to 42 psi with the system drained.

 

[Silly Rabbit]

Thanks - it is 70% with factory setting of 50psi operating pressure and 35psi on tank bladder . Looks like installer or previous owner lowered the pressure. Not sure why. It will be interesting to see what the tank is reading after I bleed the system.

 

[Bannerman]

A typical under sink RO system will utilize an ASV (auto-shutoff valve) that will stop production when the RO storage tank pressure rises to 60% of the incoming supply pressure. With 40 psi supply pressure, the ASV will cease production once the storage tank pressure has risen to only 24 psi.

A method to increase RO efficiency is by utilizing a small electric booster pump to increase the RO supply pressure to 80+ psi. With 80 psi to the RO unit, water production will continue until the storage tank pressure rises to 48 psi. Regardless of the supply pressure to the RO unit, to optimize the RO storage tank's water storage capacity while ensuring sufficient pressure to rapidly push 100% of the water from the tank, the air pre-charge pressure should be calibrated to 7 psi while the tank is completely empty of water.

Aquatec offers a line of quality RO booster pumps that are commonly utilized for such applications.
Aquatec RO Booster Pumps

 

[Valveman]

When you get tired of the problems caused by the variable speed controller and that dinky little switch you can switch to a Cycle Stop Valve. The CSV will give you even better constant pressure and doesn't cause all the problems and expense of a VFD.