Dear Mr. Zegait, If you ...
Published by Nils Tellier, Principal
Dear Mr. Zegait,
If you need to correct water-hammer on an existing system, you can add an air tank - teed off the water line - and let the water pressurize the air in the tank during the pressure surge.
The air tank Maximum Allowable Working Pressure (MAWP) should ideally be higher than the pressure spike from the water hammer. However, you can also use an air tank of lower pressure rating and let the pressure relief valve vent the excess pressure (this is not optimal obviously).
The air tank volume can be determined by the theoretical delay in valve closure to reduce the hammer pressure wave: a) if the valve closed in x seconds instead of instantly, what volume of water would be flowing through? b) what is the acceptable volume reduction for the air before its pressure reaches the tank MAWP? This is the minimal volume for your tank.
As for everything else, try to oversize the air tank volume and MAWP.