high initial pressure

all areas of the house have high initial water pressure then the pressure/flow drops after a few seconds. I have just replaced the pressure regulator thinking it might have been bad. Was also getting major hammering/noise when a faucet barely turned on (thinking it had too much pressure on it) Any other thoughts? I am definitely not a professional plumber, just a pretty good handy man. So I would really appreciate any assistance or ideas. Below are the house stats:
3/4 in copper in mech closet. presumably 1/2 in. to services 18 yr old house on slab, single story. no thermal expansion tank. hot water heater fairly new (built in 1994 according to EPA sticker). On unregulated faucet(front of house) great pressure/flow.
My wife and I just bought this house, so I can't give anymore history.
Thank you very much for your time. My email address is snipped-for-privacy@earthlink.net
Jack
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If the pressure regulator does not have a built in bypass and/or there is a check valve on the water meter, then you need the thermal expansion tank. More info will help. can you get pressure readings on the hot and cold sides? Are they the same? Is one higher than the other? Does the pressure clime right away? or does it take awhile? Could also be bad pressure regulator or something else. Dale

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If you are getting a water hammer at one faucet you should check the faucet and or shut off on that faucet for junk in the line. This will cause a water hammer like noise.If it is at any faucet, check any valve up stream. Any difference between hot and cold?
Randy
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