PDI WH 201 PLACEMENT OF WATER HAMMER ARRESTORS

[member22]

The PLBG Inspector asked for WHA to be installed on Hot Water branch with two lavatories and in a toilet rm with one lavatory. Both branches do not extend more than 5 ft from the vertical drop.
First I don't consider the lavs as a quick closing valves and I provide WHA only on the Cold Water branches with Flush valves.The PDI WH 201 have examples with Lavs and shows WHA's on the HOT WATER branch. Am I missing something?
Need help in understanding which plumbing fixture will be considered to have quick closing valve and will require a WHA on the hot water line.
Thanks

 

[PEDARRIN2]

I would tend to agree with your assumptions - I have never put an WHA on a hot water line.

Generally, I design the cold water lines to not need them either.

Sounds like the inspector is trying to show his authority.

Are the lavatory faucets electronic or manual. Sometimes, the electronic faucets can be considered quick closing. It also depends on what pressure you have in your piping. This seems to affect water hammer at times.

 

[ChrisConley]

I'd argue that a manual lavatory handle could be considered quick closing as well.

 

[PEDARRIN2]

I would not dispute that some lavatory handles could be closed quickly - but I don't know that the flows would warrant a WHA.

A flush valve flows 25-30 gpm - very quickly so you can get the 1.6 or less gallons per flush.

A private lavatory flows 1.5 gpm, which is typically split between hot and cold so you might have a maximum of 1 gpm in a single pipe. Public lavs flow one third of that so the flows are even lower.

Pipe size is smaller for lavatories than for flush valve fixtures.

I have never done the math for lavatories - I usually design larger manifolds for flush valves so the velocities are low.

 

[TrippL]

Why would you put a hammer arrestor on the cold line and not the hot line? The potential flow through the hot line is the same as the potential flow through the cold, is it not? So if you determine that a hammer arrestor is warranted for the cold line to the lav, then why would it not be warranted for the hot?

Also, even if a shock wave (watter hammer) will not be formed in the pipe from the closure of the valve, there will still be a pressure spike in the pipe which will cause movement in piping that is not properly restrained. I have had a 1/2" pipe (hot or cold) to a lavatory faucet (1.5 gpm) bang against the stud wall when the standard lavatory faucet was closed relatively quickly.

If I saw that arrestors were placed on the cold line to the faucet, then I would question why they are not on the hot.