The irrigation valve on my custom pool autofill system makes a loud thunk when it shuts off, going through the entire house.

I installed a water hammer arrestor to cut the sound down and protect the plumbing from damage.

It eliminates the vibration from the thunk which used to be felt through the house. The valve is still pretty loud when it shuts off, however.

EDIT:
The vibration from the valve shutting off can no longer be felt through the house, but the sound of the valve closing can still be heard. A big improvement!

A more knowledgeable viewer let me know that I should not have used galvanized steel with water, and I have changed the side exit elbow and galvanized nipple out for PVC, using a 1 inch slip fit side exit elbow with 3/4 inch treaded bushings glued into the slip fittings. I couldn’t find a 3/4 side exit elbow with threaded connections, so had to build one. I will post that video as an update.

Thanks for the helpful comments! This is a great way to learn and make myself better!