Hammer arrestor

[Leslie]

I'm installing a new water heater and I see a hammer arrestor on the hot water line
as it leaves the current heater.
From my understanding of an arrestor's function I see no possible function for it.
Can someone clear this up for me please ?.

 

[phishfood]

Is it a hammer arrestor, or an expansion tank?

If it is a hammer arrestor, is there a washing machine relatively close, piping wise, to the water heater?

 

[johnjh2o]

I would say it was put there for a reason. My guess is there was a problem with water hammer in the water lines.

John