On my water pipe system, there is this bell shape thing with a bolt on
the top. I always thought it a water pressure regulator.

The other day, the engineer of my community came to check my water
system. He said that thing is not a water pressure regulator but a water
pressure reducer. According to him, a water pressure regulator is a
device that would keep output water pressure constant. If the outgoing
water pressure is set to, say, 50, no matter what the main pressure is,
be it 100, 90, 80, or 70 psi, the output is always 50 psi.

A water pressure reducer, according to him, is a device whose output
pressure is affected by the input pressure. If the main pressure is,
say, 80 psi, and the output pressure is set to 50 psi, when the main
pressure is increased to 100 psi, the output pressure would also increase.

Does he make sense?