That way if the pressure gets really high, say 150 PSI, a tiny valve could open and let a trickle of water through. And this isn't exactly rocket science. A relief valve is simply a spring, a ball or needle device, and a precision-machined seat. Every faucet made could include a high-pressure relief valve on both the hot and cold sides. Every faucet in every house in this country will eventually be replaced.
People replace faucets because of changes in style, because they are remodeling.
People don't often make major changes to their plumbing, such as install water-hammer arrestors. Since the insurance industry spends a lot of money on water damage from burst pipes, you would think they would pressure the plumbing code officials to adopt rules requiring all faucets to employ a built-in pressure relief valve. Eventually we all might save a little money. Send us your thoughts.