Main Water Feed - 20psi Pressure Drop When one Fixture is Open

[stoopalini]

Also keep in mind I had valves 2 and 3 closed for one test, and pressure at point C was 80psi static, and dropped to 60psi when the spicket at D was opened. So this eliminated the house plumbing altogether.

 

[Reach4]

So there is some drop in the city system. There is some drop in your system. How far is it from B to the bypass?

I understand a PRV is to protect against presssure spikes, or increases, but not regulate against a pressure drop. I didn't think they were able to maintain the set pressure if the incoming static pressure that was used to set the spring tension, dropped.

The PRV should adjust if the incoming pressure drops. Some will do it better than others. Unfortunately there may not be any that are really good at that, because there does not seem to be much touting of superior performance. Of course I may have missed it.

The most common reason for high pressures, that require house PRV use, is to allow cities to have fewer pumping stations and/or water towers to serve areas of varying altitudes.

Your suspicion that the regulating ability of a PRV is lousy may be correct. After looking around, I don't find a specification similar to "power supply rejection" specs for electronic regulators. Still, having the regulator farther toward the load would let the PRV do its best with its limited regulating ability.

When they did the test and the pressure dropped to 65, you don't know how much water they were running during the test. If that was 20 GPM, that is probably a much higher rate than when you do your own test at 5 to 10 GPM.

When you get a pressure gauge on B, you will have more meaningful info.

 

[Sponsor]

 

[stoopalini]

The distance from B to the bypass is about 40 feet. And correct, I don't know the GPM of the test they ran. They used a pipe with a typical outdoor spigot on the end though. I imagine it would be the same, or similar, in GPM to my outdoor spigots.

I've run tests with using both the outdoor spigot to flow water, and using the garage sink. In both cases the psi drop is 20. I would imagine the garage sink isn't flowing much more than 2 or 3 GPM. It's an older fixture designed for a kitchen sink.

As another data point, I just went and tried another test while in the middle of wresting this reply. I connected the gauge to pont E: static PSI was 78. Then I turned the master shower on, with both heads flowing cold water, and it dropped to 58psi. This should be about 6gpm or so, just based on the new shower heads ratings. Then I turned the shower off, and the PSI went back to 78. Then I opened one of the cold taps on a bathroom sink, and the PSI dropped to 60.

The bathroom sink fixture is also new, and is probably flowing 1.5gpm or so, just based on the specs of the fixture.

It appears the GPM demand isn't having a large impact on the pressure drop.

 

[Themp]

The city is providing, flowing 65 psi. And at point E with a lav or shower on you have around 58-60 psi flowing. Your 20 psi drop is really just 5-7 psi. Comparing static to flowing is not the correct way to look at your pressure loss.

You could look at getting a booster pump:

http://www.familyhandyman.com/plumbing/boost-low-water-pressure-in-your-house/view-all

 

[stoopalini]

My concern is in order for me to get that 60psi useable pressure, I have to have the PRV set to 80psi static pressure.

I'd prefer to set it to 60, and then keep 60 when it's flowing, for less wear and tear on the fixtures, as well as to lose the immediate 80psi burst when a fixture is opened.

Would there be any method to stabilizing the static vs. flowing pressures by utilizing two PRVs in series? (Since I now own two of them anyway). With the 1st set to 80, and the second set to 60? Or would this just result in more fluctuation between static and flowing?

From everything I've read, the static pressure shouldn't drop with a single fixture open if everything is correct. I'm trying to figure out how I can have static and flowing pressures equal, or very close.

 

[Jadnashua]

How long is the pipe from the city's main, and what size pipe is it? Keep in mind that static pressure will be the same with a 1/8" pipe as a fire hose, but the fire hose will have a lot less pressure drop along its length when water is flowing than that 1/8" pipe. A significant drop in flowing pressure implies inadequately sized main line. If there's any old galvanized that has corroded, or if say copper or a plastic pipe, it could have been crimped along the way, either will restrict the flow.

 

[stoopalini]

I'm told the main is a 4", and then a 3/4" copper is tapped in to feed my house. It comes off the 4" and runs about 100ft, then turns 90*, and runs another 6ft or so to the meter. After the meter, there's about 40ft of 3/4" PVC to the water softener bypass valves.

There's no galvanized pipes to my knowledge. The neighborhood (and I'm using that loosely, as I'm in the country) was established in 1997. So the water infrastructure isn't very old.

I agree it appears the main eithernisnt sized properly, or there's an issue with how the 3/4" pipe is tapped into the 4". The city workers told me it was most likely a "hot tap", but I'm not quite sure what that really means?

 

[Jadnashua]

A hot tap is done while the line is in use rather than shutting things down, draining the pipes, then making a connection like you'd do in your home via soldering it. This takes a different fitting and methodology to accomplish than soldering. It would be inconvenient to impossible to shut and drain things every time they needed to make a new connection unless they could do say a full housing development, then connect it to the main line.

 

[stoopalini]

Makes sense. My plumber was suggesting the hot tap itself may have some sort of restriction in it causing the pressure drop. After the holiday season, I am going to call the city back out and present my findings to them. And do another presssure test on the ouput side of the new meter.