Home Improvement → Re: Plumbing: valve requirement for main shutoff?

Why would a gauge see sudden changes in pressure installed after the pressure regulator?

Valves slamming shut, etc.

Why won't the expansion tank even that out?

It can't respond quick enough.

As usual, it depends on the particular configuration of the plumbing system...

Snubbers are cheap, worth the extra expense.

I've never had a problem but I will trust your expertise.

OP -- don't forget that you need to install an expansion tank if you installed a pressure regulator.

It all depends what kind of water usage happens on the downstream side of the pressure regulator. Any appliances with electric valves can create water hammer (dish washers, washing machines) due to the instant changes from off to full flow and vice versa. The bigger the flow the more pronounced the sudden change in pressure.
Around here I have seen homes where the sprinkler valves for the yard irrigation are connected to the water line after the pressure regulator. It is not unusual to see a 5/8" water meter and pressure regulator followed by 3/4" or 1" sprinkler valves. Even the best pressure regulator will have difficulties maintaining steady pressure under those conditions.

Plumbing - what a variable. Most city water supplies are around 70psi - not an issue for modern homes. Also important is the flow rate inside the house. I had our county/city water company come out to check my water pressure/flow - they do this for free. The hooked up a hose bibb to their side of my water main - had 70 psi and 15gpm flow. After my builder installed pressure regulator valve they showed I had 68psi but 4gpm flow! They said that was why the person taking a shower yelled when a toilet was flushed somewhere in the house.

Anyway, we have a pretty constant pressure (no great fluctuations) so I cut out the PRV (PEX pipe) and things seem to be better with the flow rate issues (I have not had the water flow tested again by the county).

I called the PRV company and talked about my flow rate issue and they said the problem 'could' be the house builder plumber trying to adjust the PRV w/o having the water turned on - they said you only adjust the PRV with water turned on (don't turn the adjust screw w/o the water on) and maybe that damaged the PRV ??? Beats me! Anyway, I have no PRV and things seem fine.

Why would you need an expansion tank if you have a regulator.

I've installed and had my workers install hundreds of pressure regulators just like that one and I've yet to ever install an expansion tank except on my fathers old hot water heat boiler.

However if you have a back flow preventer on your supply line then you need a tank but since you don't have one I assume there is no BFP on your supply.

expansion tank typical installation

It would even it out. That's what it's for.