# Residential plumbing-pressure regulator **URL:** \ **Category:** Factual Questions\ **Created:** [July 10, 2016, 12:07am UTC](https://boards.straightdope.com/t/residential-plumbing-pressure-regulator/759518 "2016-07-10T00:07:50Z")\ **Posts on this page:** 5\ **Page:** 3
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [July 11, 2016, 10:41pm UTC](https://boards.straightdope.com/t/residential-plumbing-pressure-regulator/759518/41 "2016-07-11T22:41:30Z")
> [@TriPolar](#): > > Does the town have any plans from when the house was built? I know it’s tough going back to the 60s, but maybe you’ll find as-built plans to help you out. I’d like to find out. When I was pricing to replace a retaining wall, one guy I talked to had some software that told him when the wall was built, who did it, his Wife and children’s names, and the phone number of his girlfriend. ---
**Author:** ![boytyperanma](https://avatars.discourse-cdn.com/v4/letter/b/4491bb/32.png) [@boytyperanma](https://boards.straightdope.com/u/boytyperanma)\ **Post date:** [July 12, 2016, 1:48am UTC](https://boards.straightdope.com/t/residential-plumbing-pressure-regulator/759518/42 "2016-07-12T01:48:27Z")
> [@jjakucyk](#): > > Are pressure reducing valves also check valves? More water utilities are requiring check valves too, and if you add one, then you’ll also need an expansion tank at your hot water heater. They’re small, like maybe a foot in diameter and not much longer, but you need to do it if you have a check valve on the main line since the hot water will no longer be able to expand back up the cold water feed line anymore. > > I’ve seen pressure reducing valves become almost compulsory here in Cincinnati not only due to the very uneven terrain, but also because increasing mains pressure is about the only way the water works can keep extending its service area to farther flung suburbs. This unfortunately also causes more water main breaks in the city as the pipes are older and also under the most pressure. PRV’s are not check valves, they just restrict flow/pressure, water can move backwards through them(usually poorly though). Check valves allow water to only travel in one direction, though by themselves are not back-flow prevention. Towns require back-flow prevention a single check valve is not sufficient as it still allows potentially contaminated water to come in contact with the municipal supply. A back-flow preventer usually incorporates two check valve with a relief in between. If a house has back-flow prevention installed water can not be forced back into the system. As a home is a closed system and water expands when heated, heating water when nothing is running increases the pressure in the pipes, this can result in damage. We install a pressure tank to absorb that difference, giving the water somewhere to expand too. The pressure normalizes whenever you open a faucet. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [July 30, 2016, 5:03pm UTC](https://boards.straightdope.com/t/residential-plumbing-pressure-regulator/759518/43 "2016-07-30T17:03:33Z")
The plumber installed a pressure regulator behind the water heater this morning. At least we won’t have hot water blow out of an appliance. ---
**Author:** ![Snnipe\_70E](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)\ **Post date:** [July 30, 2016, 6:19pm UTC](https://boards.straightdope.com/t/residential-plumbing-pressure-regulator/759518/44 "2016-07-30T18:19:04Z")
> [@carnivorousplant](#): > > My Mother’s house was built in\*\* 1955\*\* with the same copper pipe buried in the slab. > Nice and quick for contractors then, it sucks for homeowners now. 🙂 1955 here is the answer why your house had no PRV (Pressure Reducing Valve). When the house was build the city water pressure was probably less than 60 psi. But as the city grew main pressure was increased to accommodate larger demand. It was increase pressure or increase the size of the water mains. In most cities, homes build after the 60’s were required to have an PRV. The water line and everything after the meter is the property owner’s line not the water company’s. In many cities PRVs become useless after a few years. In San Jose an new PRV works fine, but in one year they begin to scale up and not work properly. After about 2 years the parts internally no longer move. But in a city like SF I don’t see where they should fail for years, it at all. For your sake I hope the plumber put in good high quality valves on both sides of the PRV and used unions. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [July 31, 2016, 12:07am UTC](https://boards.straightdope.com/t/residential-plumbing-pressure-regulator/759518/45 "2016-07-31T00:07:17Z")
> [@Snnipe\_70E](#): > > For your sake I hope the plumber put in good high quality valves on both sides of the PRV and used unions. One end has a built in union. I don’t know enough about plumbing to name it. A sleeve and washer that hold it to another pipe. The other end connects to the water heater input with a hose that be unscrewed from both ends. If a valve wasn’t required in 1958, you may have hit it on the head. Pressure did go from 80 PSI to 105 PSI when I began the thread. I’m thinking that a regulator valve failed at that time. [Previous page](https://boards.straightdope.com/t/residential-plumbing-pressure-regulator/759518.md?page=2)