Hi I have recently replaced a t&p valve that had a leak and now the drip has returned about a week after the installation. I'm thinking there may be a issue with the expansion tank. I got a 0 psi reading from the exp tank which i assume means I need a new one. I got a reading of 85 psi from my outside hose spigot and have a prv installed that ranges from 25-75psi. My question is do I need to set the new expansion tank to match the psi of 85 at the spigot or match it based upon the prv psi range?

Your expansion tank should be set to 10 psi over the pressure reading from you pressure regulated water at the hose bib. Do not take a reading before the pressure regulator or you will get the pressure your water company provides at your curb. I suggest setting your pressure regulator to 60 psi first, then filling the tank with 70 psi. YOU MUST SHUT OFF THE WATER AT THE VALVE BELOW THE PRESSURE REGULATOR AND BLEED DOWN THE PRESSURE THROUGH YOUR HOSE BIB BEFORE YOU FILL YOUR EXPANSION TANK WITH 70 PSI OF AIR. READ THE ABOVE SENTENCE AGAIN AND THEN PROCEED!

1. Set pressure regulator to 60 PSI.

2. Shut off valve below the pressure regulator.

3. Open the nearest hose bib to relieve the pressure on the house line.

4. Fill the Expansion Tank to 70 psi.

5. Open the shut off valve slowly and have someone open faucets, shower valves, etc inside to bleed the air out of the system.

6. After air has been expelled, close all faucets and shower/tub valves and hose bibs...close all valves that were opened.

7. Check your water pressure at the hose bib to verify it is at 60 psi.

Now your Expansion Tank should work properly. Good luck.

Many water meters have a check valve preventing water from coming back thru the meter and in those circumstances, you will have a closed system and the Expansion Tank is absolutely needed. Make sure it is sized correctly. Most manufacturers furnish a chart showing what is needed by pressure and size of water heater.

Doesn't Watts and the other manufactures state to charge the tank the same as static pressure and not 10 psi over?



Edited 2 times.

to quote one os john wayne's kentuckians at the alamo.. "it do"..

So both of my hose bibs on the outside of the house are reading 85 psi. Should I set the expansion tank to 85 psi? Or could this possibly mean there is a issue with my prv?

It is somewhat immaterial as long as the tank has air in it. Too little and is effectiveness is diminished. Too much and the benefit does not kick in until expansion raises the pressure to match the tank.

The manufactures of the expansion tanks say not to exceed 80 psi charge.

which juuuuust 'happens' to be the code max for plumbing fixtures

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638