Selection and Installation of Thermal Expansion Tanks
See Part 2 for the calculation of the expansion tank volumes. Now, using the calculated acceptance volume and the tank’s total volume, select an expansion tank from the manufacturer’s data that meets these requirements.
Be aware that in most states, unfired pressure vessels larger than a certain volume must have an ASME stamp. Check your state’s requirement for this limit. If the expansion tank you need exceeds this limitation, it must be constructed in accordance with the requirements of ASME Section VIII. ASME-rated vessels are much higher in cost than non-ASME vessels. Installing multiple smaller tanks, which are below the volume limitation for ASME tanks, is also an option. Most tank manufacturers offer both ASME and non-ASME thermal expansion tanks.
Where the thermal expansion tank is installed in a plumbing system is important. The options are to install the expansion tank in either the cold- or hot-water piping. The tank will perform its intended function when installed in either location. However, the cold-water piping is the preferred location because the water temperature is lower. Lower operating temperatures will extend the life of the tank bladder.
The expansion tank should be installed in accordance with the manufacturer’s installation instructions. The tank can be installed in either vertical or horizontal orientation. If installing the tank in the vertical orientation, install a pipe support on the main piping near the tank connection. If the tank is installed horizontally, support it directly from the structure to avoid excessive stress and potential piping failure.
Prior to pressurizing the piping system, the expansion tank should be charged to a pressure equal to the plumbing system’s line pressure.
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