How To Adjust the Pre-Charge Of a Thermal Expansion Tank

Watts Workshop Quickfix Adjusting the Pre-Charge of a Thermal Expansion Tank Today we will discuss the proper procedure for adjusting the pre-charge on our DET and PLT portable expansion tanks. These tanks come pre-charged from the factory at 20 PSI; however, it’s very important that the pre-charge be adjusted prior to installation. Too low of a pre-charge will result in premature tank failure. Too high of a pre-charge will result in inadequate protection from thermal expansion. The pre-charge should match the water pressure inside the building. To determine the water pressure inside the building, we suggest that you use a Watts IWTG Gauge. This gauge can be connected to a washing machine connection, an outside water spigot, or any convenient drain inside the plumbing system. Simply install the gauge, open the drain or open the valve and read the pressure on the gauge. Once the pressure is determined, in this case, let’s assume its 55 psi, we will need to increase the pre-charge of this tank from 20 psi to 55 psi. We can use any standard tire pump to do this whether it would be a hand pump or an electric pump. In this case, we’re going to increase the charge from 20 psi to 55. Once we have pumped up the pre-charge, we can check it with our air pressure gauge and make sure that it matches our water pressure inside of the building. Recap: Adjusting the Pre-Charge 1. Determine the pressure of the system. 2. Remove the protective cap from the air inlet valve on the expansion tank. 3. Using a tire pressure gauge, check the pre-charge of the tank. 4. If necessary, adjust the pre-charge of the tank so it matches the system pressure. 5. Double-check the new pressure of the expansion tank using the tire pressure gauge, ensuring it matches the pressure of the system. 6. Replace the protective cap. 7. Follow proper installation instructions. Once a tank’s pre-charge is adjusted to match the water pressure inside the building, the tank can be installed and placed in service. We also recommend that once a year, the pre-charge on the tank should be tested. The proper procedure for doing this is to isolate the wet side of the expansion tank diaphragm from pressure in the plumbing system. This can be done by turning off the water main and opening a faucet. Once the pressure is relieved of the top of the diaphragm, the pre-charge can be accurately checked and adjusted as needed. Recap: Testing the Pre-Charge 1. Turn off the water main. 2. Open the faucet to relieve system pressure. 3. With the tank inline, remove the protective cap from the air inlet valve and check the pre-charge using a tire pressure gauge. 4. Adjust as needed. For additional information on this procedure, please refer to the instruction sheet included with the tank. The instruction sheet is also available online at www.watts.com.