Adjusting the Pre-Charge Pressure of a Captive Air Tank, Bladder or Diaphragm Type Tanks.

Adjusting your captive air pressure tank's internal “Pre-Charge” Pressure

#1 - Close the main shut off valve to the house plumbing system. Failure to close the main shut off valve will result in the whole plumbing system draining back while you do your pressure tank draining and pressure checks.

#2 - Remove the protective air valve cap and check the pre-charge pressure using a suitable pressure gauge. The tank should be at room temperature and must be completely drained to ensure it is empty of water. To be sure the tank is completely empty, the pressure gauge should indicate zero PSI, no more water is coming out of the tank, and the well tank sounds hollow when you knock on it.

#3 - When empty, close the drain valve at the bottom of the tank.

#4 - Recharge the pressure tank. The same port you used to test the air pressure at is the same one used to re-fill it. Simply attach the air compressor hose to the air valve and begin to add air to the pressure tank.

IMPORTANT: Pressure tank and pressure switch installation instructions will often advise to release or add air as necessary to make the pre-charge pressure equal to 2 PSI minimum below the pressure switch cut in setting. However, the 2 PSI is the absolute minimum for a 20-40 switch, it is not enough for a 40-60 switch which should be 5 to 6 PSI below. Some information suggests that 10% - 20% below the pressure switch cut-in setting is a suitable range. We suggest that the mid-range of 15% will be sufficient to minimize problems due to small inaccuracies between the system pressure gauge and the air pressure gauge you are using, as well as changes in ambient temperature as seasons change.

Note: Pressure switch settings may be slightly out-of-adjustment. For example, if labeled 30/50, it may be 28 or 29 to 48 or 49. See how to adjust your pressure switch using the link below:

#5 - Stop adding air when you reach the desired pre-charge set point. The chart below provides the suggested tank pre-charge based on the common pressure switch cut-in setting.

#6 - Reinstall the air valve cap back on the valve stem. Make sure the cap is on tight to prevent any air from escaping over time if the air valve were to leak slowly over time reducing the pressure inside the tanks air chamber.

Turning the pressure system back on after setting the tanks pre-charge.

#1 - Keep the main shut off valve to the home plumbing system fully closed.

#2 - Keep the tank drain valve fully closed to prevent a wet floor.

#3 - Reinstall the pressure switch cover back on the pressure switch, make sure it is secure before you turn the power back on to the water pump to prevent any risk of electrical shock.

#4 - Turn the power back on to the pump. You will hear the well pump turn on if you have a jet pump close by and it will start filling the tank. Or if you have a submersible pump, you will hear water entering the tank and will see the pressure gauge start to show the pressure increasing.

#5 - When the pump shuts off (cut-out pressure is reached), move to the next step.

#6 - Slowly open the main valve to the plumbing system.

#7 - Purge all the air from the plumbing system. After a home’s water is shut off there will be sediment and air that needs to be bled from system. It is best practice to start at laundry tub faucets and other faucets without aerators and work your way around the house running water from all the faucets. If the water runs with a bit of sediment or if you notice air blowing out of the faucets no need to worry, this is expected after making these pressure tank adjustments.

#8 - Double check that you have the main shut off in the fully open position and that there are no leaks at the tank's drain valve.

Additional Resources:

https://support.boshart.com/how-do-i-adjust-a-pressure-switch

https://support.boshart.com/i-have-totally-messed-up-my-pressure-switch-settings-now-what

https://support.boshart.com/pressure-switch-wont-turn-on

https://support.boshart.com/wiring-a-pressure-switch

https://support.boshart.com/important-things-to-you-must-know-when-installing-a-tank-tee-on-your-new-pressure-tank

https://support.boshart.com/trouble-shooting-my-water-flow-stops-before-my-pump-starts