4-Gallon RO Tank Pressure – What PSI Is Ideal?

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RO tanks operate under pressure to avoid the need for a pump to push water from the tank up to the faucet. The tank’s internal pressure needs to be maintained within a specific range for the system to function.

4-gallon RO storage tanks operate in the same fashion as any other sized tank, so the pressure must be monitored and repressurized if it drops too low. Storage tanks will gradually lose pressure over time, so this is something worth learning to do before your tank stops working.

Let’s take a closer look at everything you need to know about 4-gallon RO tank pressure including how to repressurize such a tank.

Key Takeaways

  • 4-gallon RO tanks – like most other RO tanks – should be kept within 6 to 8 psi when empty to function properly.
  • The pressure should be monitored and the tank repressurized if the pressure level drops below 6 psi. This is a fairly simple process that can be done with an air compressor/bike pump and a pressure gauge.

4-Gallon RO Tank Pressure – What PSI Is Ideal?

The size of the tank doesn’t make much of a difference when it comes to the ideal air pressure inside a reverse osmosis tank. Generally speaking, these tanks should be kept within 6 to 8 psi when measured empty.

This is just a general recommendation though, so be sure to check your tank’s label or product manual for the precise number.

How Much Pressure Does a 4-Gallon Reverse Osmosis Tank Have When Full?

The pressure in a full 4-gallon RO tank will be around ⅔ of the feed water pressure in your home. In other words, the higher the pressure in your plumbing system, the higher the pressure of your storage tank when full. For example:

  • Feed water pressure = 40 psi; full tank pressure = 40 psi * ⅔ = 26.7 psi
  • Feed water pressure = 60 psi; full tank pressure = 60 psi * ⅔ = 40 psi

water pressure gauge

How to Pressurize an RO Storage Tank

Pressurizing a reverse osmosis tank is a fairly simple process that only requires a few basic household tools you likely already have lying around.

All you need are the following tools:

  • Bicycle pump or air compressor
  • Tire pressure gauge
  • Bucket and/or rags

Have everything collected?

  1. The first thing you’ll want to do to repressurize your tank is shut off the feed water supply
  2. Now open the RO faucet and drain as much water out of the tank as possible.
  3. Close the tank valve.
  4. Then, disconnect the storage tank from the tubing and take it somewhere you don’t mind getting wet, like outdoors or in a bathtub.
  5. Open the tank valve on top of the storage tank once more, and allow the water to flow out until it slows down to a trickle.
  6. At this point, use a bicycle pump or air compressor on the tank’s pressure valve to push out any water left behind in the tank.
  7. Now, you can check the pressure inside the tank using a tire gauge or something similar. If the reading is below 6 psi, then you’ll need to add pressure to the tank using a bicycle pump or compressor until the gauge reads about 7 psi. Do this slowly and measure often so as not to overpressurize.
  8. When you’ve hit 7 psi, reconnect the tank valve with the tubing connection, turn on the tank valve and feed water valve, and allow the tank to fill before using.

Why Do RO Tanks Lose Pressure?

RO tanks lose pressure for the same reason bicycle or car tires gradually lose pressure over time: Air will seep out of the tank given enough time, at which point you’ll start to notice that the water coming out of your RO faucet is flowing slowly.

The good news is this is a normal function of the storage tank, so there’s no need to worry. If you start noticing the tank is losing pressure rapidly, this is indicative of a more serious issue like a ruptured tank bladder, which requires replacing the tank entirely.

How Does a 4-Gallon RO Tank Work?

4-gallon RO tanks – like all RO tanks – are hydropneumatic, which means they operate under pressure and can send pressurized water whenever needed. Hydropneumatic tanks contain both an air and water chamber inside them separated by a rubber bladder.

Because RO systems are slow at filtering water, a storage tank is required to keep enough water on hand to fulfill your needs. Without a tank, you would be waiting around for 5 minutes or more every time you needed to fill a glass.

Another important function of the tank pressure is triggering the automatic shut off valve (ASO). This is the valve that tells the system to stop filtering water when the pressure in the tank reaches a certain level. Without this valve, your reverse osmosis system would continuously produce water and dump it down the drain – wasting an excessive amount of water.

If you have any questions about 4-gallon RO tank pressure please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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