Water pulsing / banging from shower

Question

So I recently remodeled my master bath. We put in a new shower head and hand held with separate control handles / valves for each. Our faucets we got was from Design House Karsen collection model number 547612.

When I turned on the shower on either the shower head or hand held the water starts pulsing and you can hear banging.

Somethings I noticed / check

1. Water only starts pulsing when hot and cold are evenly mixed ( handle is directly in the middle) and stops when I change temperature from this "spot"

2. If I turn handle to hot and slowly turn back down there is no pulsing.

3. If I turn on a faucet at the sink before I turn on the shower there is no pulsing or banging.

4. Water pressure which is from city, is at 80 psi. I was told that the pressure is kinda high but i have no PRV.

5. I talked to the contractor who put in everything and said that either the valves or cartridges could be faulty so he called Design House and got replacements.

So my question is if the valves and cartridges arent faulty (which I suspect it isnt.) Could it be the water pressure or something totally different??

Answer 1

It sounds like water hammer to me. With just the right flow it can get very loud. There are 2 ways I know of to eliminate this:

1. Have a section of pipe at the faucet that goes up and is capped. The trapped air creates a cushion which can solve the problem.
2. Or use a commercial water hammer arrester. These do basically the same thing and are smaller but cost more.

Answer 2

Sounds to me like there is cavitation in the waterlines likely caused by a venturi effect where the water pressure from the hot line is trying to make the cold line produce more water than is available. This could be caused by using undersized lines, an obstruction in one of the supply lines, or by the fact there is too much pressure.