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Water pressure regulator - relative or fixed/absolute reduction?

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  • Feb 15th, 2021 2:04 pm
[OP]
Deal Fanatic
Jul 7, 2017
5656 posts
2494 upvotes
SW corner of the cou…

Water pressure regulator - relative or fixed/absolute reduction?

I have a pair of Watts pressure regulators in my plumbing system, one for the hot and one for the cold water feed (didn't have a 1" PEX tool at the time and the tool would have costed more than a 2nd regulator).

Recently added in water pressure gauges for hot and cold post-regulator. In doing so, I find it interesting that the water pressure can go up and down in an at-least 5 psi range. Note: gauge on the hot water side is before the heater, where I have since installed an expansion tank (these things are apparently optional in B.C.).

So, wondering if the pressure regulators are (supposed to be) relative, i.e., reduces pressure by 20 p.s.i., or absolute/fixed, i.e., reduces pressure to 50 p.s.i. , or some other, say reduces pressures to 50 p.s.i. if supply is 80 p.s.i. but to 53 p.s.i. if it is goes to 85 p.s.i?
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4 replies
Deal Expert
User avatar
May 10, 2005
36055 posts
10149 upvotes
Ottawa
Pressure drops if you turn on a faucet or tap.
Not sure what you are trying to accomplish or information gathering purpose with the regulators and gauges. Incoming pressure is static and then goes into a hot water tank and will differ form that.
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Sr. Member
Jun 4, 2020
524 posts
441 upvotes
Clarington, ON
Without a model number, it's not possible to be sure.

What you are describing sounds like it regulates to 50psi. Despite being a 50psi regulator, there may be some tolerance to it, for example +/- 5psi. This is normal in manufactured parts like this. To get something that has tighter tolerances involves spending more money for a more "precise" regulator.

Further, as @Pete_Coach indicated, there will be pressure drop from your supply when you use water - if your supply pressure is quite close to the regulated pressure, it is quite realistic to see the pressure indicated on gauges to drop.
[OP]
Deal Fanatic
Jul 7, 2017
5656 posts
2494 upvotes
SW corner of the cou…
KevinM56081 wrote: Without a model number, it's not possible to be sure.
LF25AUB
What you are describing sounds like it regulates to 50psi. Despite being a 50psi regulator, there may be some tolerance to it, for example +/- 5psi. This is normal in manufactured parts like this. To get something that has tighter tolerances involves spending more money for a more "precise" regulator.
I was aiming for 50 PSI which is what it is supposed to be set for.

there will be pressure drop from your supply when you use water - if your supply pressure is quite close to the regulated pressure, it is quite realistic to see the pressure indicated on gauges to drop.
I get that but it isn't a supply pressure drop due to my usage. If I leave all water use off and let it sit, the cold water pressure varies. I used the gauges to set to adjust the regulators, and also to see how it is changing . Was just surprised to see the pressure varying. Prior to installing the gauges, I noticed flow/pressure to one outlet had increased (easy to discern because it shoots straight up) after it had dropped when I installed the regulators.

Could be how the water is supplied. I had just assumed that the water was pumped uphill (some 80m - I know where the pump stations are). Now i am thinking it is pumped to reservoirs in a few high points (~162 m ASL) which is only a few m above me, or another one 30-35m higher (the supply map seems to indicate the supply my street is connected to the reservoirs by two different lines, and the reservoirs are connected to each other.

Screenshot 2021-02-15 091743.jpg

To give an idea of scale, the map is about 4-5 Km across.

I guess it could be one of the neighbours (includes a small college, a school and a federal institution) using a lot of water. School is between the two close-together pump stations and a reservoir. College and federal institution are off another branch line on the bottom right corner.

FWIW, I know the neighbours who live ~38m in elevation below me. Hate to think what their water pressure is (water pressure increases 14.6 psi per 10m). The former neighbour who was a councillor and sat on the regional district's water board (as well as worked to get water brought to parts of the municipality prior to being elected) tells me the household supply pressure can be as high as 130 psi. The last few times I checked, it was coming in at ~65-75 psi at my house.
Cream rises to the top. So does scum.
Sr. Member
Jun 4, 2020
524 posts
441 upvotes
Clarington, ON
Being an adjustable valve, it has a spring in it. This is reasonably calibrated, but isn't a NASA grade piece of equipment. There is some tolerance and some room for error in this setting. The spring gets worked as you regluate the pressure.

Additionally, looking at cold water for example - the 5 degree celcius water passes through the valve and is regulated to 50psi. You don't use cold water while you are at work, so over that 8 hours the "regulated" water has a chance to warm up to room temperature (or very close to it). When it warms up, the pressure increases on the regulated side of the valve. Due to the fact that the city pressure is at least 65psi as you indicated, it can't flow back, so some pressure is built up in excess of your 50psi setting.

I don't feel that the capabilities of the infrastructure outside your home have anything to do with it as you have installed a pressure regulator already.

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