Sean,
When installing a pressure reducer, it "closes" the system.
Shock arrestors should be added at the washer, dishwasher and the icemaker.

: I'm on city water and I had a PRV installed because the water pressure was very high. After the PRV was installed, valves in my house still make a clunk noise when they are shut off (faucets, ice maker, washing machine, etc.). I thought the pressure might still be too high, so today I put a pressure gauge on an outlet and it read 55 psi. I think this is pretty normal. Would it hurt anything if I dropped it down 10-15 psi? I don't know if ther would be any hazard to my boiler or heating system or anything else I can't think of. Thanks for your help!