I think Rich is talking about a very different pressure system found on some old coaches where they used an air compressor to pressurize the potable water system.
With your water pump- based system there are two things you can do-- with different results:
Add an accumulator with bladder. Set PSI at 2 PSI less than cut-in pressure for the pump. For many, that means setting it at 23 PSI with city water off, pump off and pressure bled off by opening a faucet. This will do little to change the noise level, but help a lot in smoothing out water pressure at the faucets. The accumulator is generally plumbed into the system with a "T" after the outlet of the pump.
To quiet the pump, one needs to have the pump attached to the plumbing with a length of flexible hose, NOT hard pipe. This is both on the inlet and outlet. If plumbed with rigid pipe, the pump noise is transmitted through the pipes. This can normally be done for around $10 worth of hose, clamp and barb fittings. In fact some pump manufacturers suggest this flexible hose installation in their installation instructions. As an alternative, sometimes using foam rubber around the hard lines will help absorb some of the vibration-- it will not be as successful as isolating the pump with flexible hose, however.
Dianne and Brett Wolfe
1997 Safari Sahara 3540
Moderator, FMCA.com Forums
Chairman, FMCA Technical Advisory Committee
Member, FMCA Long-Range and Development Committee 2007-2009
Moderator, http://www.dieselrvclub.org/(FMCA chapter)