Resolution? Why is there an air tank on the water lines?

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Originally Posted by SJM-007

Resolution? Why is there an air tank on the water lines?

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This is a expansion tank,(see image) They're installed on the cold water line to handle the expansion of hot water when the water system is closed by a check valve or a back flow preventer. If you have a closed system and do not have a expansion tank the expanding hot water will trip the T&P valve on the water heater. Hope this explains things. Tom

Okay, thanks, yes that explains the air tank.

However would the functionality of the expansion tank have any effect on a water hammer in the system. When I heard the water hammer before in pipes upstairs, I drained the hot water heater and flushed (50 gallon tank). Noticed deposits of sediment from the tank and possibly the lines, however after I bleed the air out of the pipes the water hammer was gone. That lasted for about two weeks, the water hammer has returned, thoughts??

The expansion tank acts like a big air chamber for the system. Its primary purpose is to allow for the hotwater expansion in your heater, however, we also installed air chambers on all our houses since the 60's. You partially recharged the air chambers when you drained the system. Let me show you how to recharge them fully. These air chambers must be recharged from time to time as they load up with condensate. "Water hammer" happens when you abruptly shut off the water. You have at least 40 pounds of pressure pushing the water flow. The weight of the water hitting a 90 degree bend causes the sound that you hear. We put in shock absorbers,(air chambers) to cushion the hammer much like the shocks on your car.
Back in the 60's we were required to to put shock absorbers,(air chambers) on all bath lavatoies and kitchen sinks. Over time water and condensate built up in them and they must be recharged. First turn off the house at the main house shut off valve. Then open hot and cold faucets at the farthest bathroom to prevent air lock.(This is important.) You will find under each fixture little brass or chrome valves. These are called angle stops. With a small pail held under the angle stop to catch the run off look under the handle of the stop and you will see a nut with the stem running through it. This is called the bonnet packing nut. Put your wrench on it and back it off counterclockwise. Now open the stop and remove the stem and washer assembly, The stop will began to drain. When it has quit draining reassemble the stop and move on to the next one. Do this on each one of your angle stops. There will be six of them in a two bath home. When you are done, close off the faucets you have opened, turn on the water to the house, and give yourself a pat on the back.
You have just recharged your air chambers and saved yourself a hefty service call bill. Hope this helps you out TOM

Thanks I will let you know how I do with the procedure. Thanks again