Installation, Commissioning and Maintenance of Expansion Tanks

When installing an expansion tank, take note of the following:

1. An expansion tank can be installed anywhere on the cold inlet line at the pump suction side of the system. In hot water and hydronic systems, it is normally connected to the cold water pipe above the water heater using a tee-fitting. It is important to position the tank far from the outlet of the water heater to avoid unnecessary heating of the tank shell via convection.
2. Ensure that the fluid entering the tank is less than the prescribed maximum fluid temperature to prevent diaphragm failure. In most expansion tanks, this is rated at 70ºC. In the case of high-temperature fluids, an intermediate tank that will act as a buffer must be installed between the expansion tank and the system.
3. The expansion tank must be installed with a lockable ball valve and drain point for easy isolation and draining during maintenance or repair. There should also be ample space around the tank for easy access.
4. A pressure relief valve should be installed between the tank and the ball valve as a safety precaution in case the pressure goes beyond the allowable maximum pressure of the tank. Hence, the pressure rating of the valve should be less than the safe working pressure of the tank.
5. If possible, mount the tank vertically with the connection at the top to minimize stress on the fitting. Aside from developing less mechanical stress compared to horizontal mounting, vertical mounting also prevents air from getting trapped in the water side of the expansion tank during initial water-filling. If it is necessary to mount the tank horizontally, ensure that the tank is well-supported.
6. Do not install an expansion tank directly below a hydraulic separator to avoid dirt from the separator building up in the tank.
7. If two or more expansion tanks will be installed, those tanks should connect to an intermediate common pipe before connecting to the main system pipe. Connecting multiple tanks to different points of the same piping can cause pressure variations, depending on where the circulators are located.

An expansion tank should be maintained at least annually to ensure optimum operation and longer equipment life. When maintaining an expansion tank, follow the steps below:

1. Visual inspection. Perform a visual inspection of the tank and check if there is any damage to the tank shell, valves, pipes, and fittings.
2. Check diaphragm or bladder integrity. Press down the Schrader valve and see if there is water coming out of the valve. If there is, the diaphragm or bladder has most likely ruptured. If it is a diaphragm-type tank, the whole tank needs to be replaced. Otherwise, if it is bladder-type, the bladder can be removed and replaced.
3. Isolate. Isolate and disengage the expansion tank from the rest of the system using the lockable ball valve. Drain the tank and ensure that it is free from dirt and foreign debris.
4. Check pre-charged pressure. Over time, air or nitrogen gas can find its way out of a sealed tank. It is important to test if the pre-charged pressure in the tank still matches the calculated pre-charged pressure required. To calculate the required pressure, visit Sizing and Design of Expansion Tanks.
5. Charge the tank. If the pre-charged pressure does not match the calculated pressure, charge it with air or an inert gas like nitrogen until the required pressure is obtained. An expansion tank can be charged via the Schrader valve, using an air compressor or a nitrogen canister. After charging, ensure that the tank and the valve do not have leaks by checking if the pre-charged pressure is holding.
6. Reconnect. Reconnect the expansion tank and re-pressurize the rest of the system. Perform final inspection and ensure that there is no leak in any part of the system.