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Expansion Tank Pre-charge Pressure Formula:
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The expansion tank pre-charge pressure is the initial air pressure set in the expansion tank before installation. It should be set to match the system's static pressure plus 2-5 psi to accommodate thermal expansion in water heating systems.
The calculator uses the expansion tank pressure formula:
Where:
Explanation: The formula ensures the expansion tank has sufficient pre-charge pressure to handle water expansion when heated, preventing excessive pressure buildup in the system.
Details: Correct pre-charge pressure is essential for protecting the water heater and plumbing system from damage caused by thermal expansion, preventing pressure relief valve operation, and extending equipment lifespan.
Tips: Enter the system's static water pressure in psi. The static pressure can be measured using a pressure gauge at any faucet or fixture when no water is flowing in the system.
Q1: Why add 2-5 psi to the system pressure?
A: The additional pressure ensures the expansion tank diaphragm doesn't bottom out and provides a buffer for proper thermal expansion accommodation.
Q2: How do I measure system static pressure?
A: Use a water pressure gauge attached to a hose bib or faucet when no water is flowing in the system.
Q3: What happens if pre-charge pressure is too low?
A: The expansion tank may waterlog, causing frequent pressure relief valve operation and potential system damage.
Q4: What happens if pre-charge pressure is too high?
A: The expansion tank may not accept expanded water, leading to excessive system pressure and potential damage.
Q5: How often should pre-charge pressure be checked?
A: Annually, or whenever you notice symptoms of pressure problems in your water heating system.