Water supply line pressure: one too low, one too high

[MichaelO]

Two connected houses in our 70s condo development, everyone served by one water meter at the road. 833 has 40 lbs of pressure while attached house 835 has over 100 lbs. -- no problems in either house or immediately outside -- and no pressure relief valves or shutoffs. Plumber traced the all-copper 3/4" line away from the house, and used "fish tape" to probe for blockages, and when the tape stopped, they dug. Found standard joints, turned the water off at the street, cut the line, measured the water pressure and then reconnected, because the pressure was unchanged.

In one of the holes, the plumbers found that another copper line ran parallel -- clearly from 833 with its 100+ lbs. pressure. So it looks like there's no main line down the center of the 75-yard driveway, branching off across from each house. Instead it sure seems each house's copper line runs towards the meter at the curb.

One plumber said we should find where the individual service lines come together near the meter, and add/replace PRVs and shutoff valves for the lines with problems -- put a concrete sleeve and cover for future access. (May need a good line locator to pinpoint the spot.)

Plumber B said you could do that later, but you could solve the immediate problem by just digging back to where the two lines run parallel near the homes, and connect them, while adding the PRVs and shutoff valves. Ideally, would add a concrete sleeve and cover there for future access. Plumber B wants to charge almost twice as much for this as Plumber A wants to do what seems the right long-term solution.

However, not everyone is convinced there really is a cluster (six homes altogether) -- who knows where subcontractors in the 70s may have located PRVs. Maybe there really is a crimped copper pipe (tree roots are suggested), which might explain the low pressure, but doesn't answer why the high pressure.

How can we decide between these two approaches?

 

[Chuck]

I may not have understood the situation properly, can you upload a sketch-plan summarising what is known about the system?

When you say "because the pressure was unchanged.", unchanged from what?

Are you sure that all the houses connect only to the shared meter? If you isolate the meter, do all the the houses lose their supplies? Have you checked that there are no leaks by monitoring the meter during a period of zero-consumption?

Are you looking for the right problem? For example, 40psi may well be the correct 'setpoint pressure'. In this country 3 bar (44 psi) is commonly used and 100psi would be considered rather high. The high pressure at #835 under static conditions may be a sign that its PRV is passing. Static pressure measurements on their own only tell part of the story, I'd want to supplement them with dynamic measurements of both pressure and flow.

I don't like the sound of "just digging back to where the two lines run parallel near the homes, and connect them". If I've understood correctly, this will create a loop in the supply, which could lead to health problems and complicate/confuse future works.

 

[Michael O]

I may not have understood the situation properly, can you upload a sketch-plan summarising what is known about the system?

When you say "because the pressure was unchanged.", unchanged from what?

Are you sure that all the houses connect only to the shared meter? If you isolate the meter, do all the the houses lose their supplies? Have you checked that there are no leaks by monitoring the meter during a period of zero-consumption?

Are you looking for the right problem? For example, 40psi may well be the correct 'setpoint pressure'. In this country 3 bar (44 psi) is commonly used and 100psi would be considered rather high. The high pressure at #835 under static conditions may be a sign that its PRV is passing. Static pressure measurements on their own only tell part of the story, I'd want to supplement them with dynamic measurements of both pressure and flow.

I don't like the sound of "just digging back to where the two lines run parallel near the homes, and connect them". If I've understood correctly, this will create a loop in the supply, which could lead to health problems and complicate/confuse future works.

Thanks for your thoughtful attention! I will upload a sketch shortly but I can answer most of your questions now. When the valve at the meter at the street is closed, all homes lose access to water-- no doubt about that. The normal pressure here is 60-65, and at 40, the residents can't use two water appliances at the same time: Wash dishes, shower is a trickle, etc. Pressure is measured at a frost-free hose bib outside each home. 100+ pressure blew out shower cartridge and toilet after the repeated on/offs at the street (very old fixtures). Connecting the two lines: as explained to me, a T would divert some of the pressure and flow from the over-pressured line into the low-pressure line. I don't see how it would create a loop. I assume the supply water follows the path of least resistance, so it goes to the 40 lb branch until pressure is equalized between the two branches-- but is there a problem when when one house is using water and the other is not? Presumably the high pressure is the result of a PRV failing somewhere up the line, but could the low pressure also result from a PRV failing?

 

[Michael O]

Forgot to add: meter doesn't move when there's no usage, so no leak. Don't immediately see how to upload sketch and photo (s).

 

[MichaelO]

Ah -- couldn't see "attach files" on my phone. I just talked to someone in the city water department who seemed to know what he was talking about: It's not low pressure, because water spurts when it first comes out--- it's low flow. So tying the two pipes together will give more water but won't reduce the high pressure. Adding PRVs there would. However, low flow has to be due to a blockage upstream, and eventually it will cause the pipe to fail, so we can't put off finding the blockage for too long. Finding the manifold would be useful in the long run, but doesn't solve the immediate problems. Make sense?