Any risk in installing a one-way valve?

Question

A few days ago, I noticed a [serious issue][1] in my home: when there was an interruption of water supply from the city, the water in my circuits was depleted very fast (running backward, passing back through the water meter), and then strong air pressure kept the water meter running backward.

I want to solve this problem. My plan is to install a simple one-way valve right after the water meter.

After the water meter, the first thing I have is a device that ensures the pressure in my house stays under 2.5 bars.

This pressure-regulated device was installed by a plumber about a year ago. I wonder if this device contributed to the problem of strong air pressure backflowing from my system.

I plan to buy a simple one-way valve like this.

and install it right after the water meter (before the blue tap). That seems pretty easy to do.

However, I am wondering if there's any downside to doing this? Could this somehow create damage to my system? My biggest fear is pipes bursting inside my house, as they would be pretty much impossible to replace.

PS: I tried to contact plumbers, but I live in the middle of nowhere, and the last 2 plumbers who came actually broke more than they fixed.

EDIT : This question has been marked as duplicate. The website suggests I delete it, but when I do so, it then advises against deleting it. So please just ignore that question.

No, because that question was about understanding the problem. This question is about a specific modification of the system. — DevShark, Nov 05 '22 at 09:43
Usually the only concern with one-way valves is connecting them in the right direction. A waste of time if connected and you find it is backwards. — crip659, Nov 05 '22 at 09:56
Does your water purveyor (utility) provide any specifications or documentations WRT backflow prevention? — ThreePhaseEel, Nov 05 '22 at 14:05
My water system has a "back flow preventer" to keep water from my pipes from flowing into the public mains. The device (which was installed by a licensed plumber) is mandatory. Is that what you had in mind? — Duston, Nov 05 '22 at 14:05
Have you called and reported this incident to your water company? I have to think they would be very interested in their system sucking the water from your home. It could be very damaging to the water heater as well as some other fixtures. — RMDman, Nov 05 '22 at 16:45
@RMDman worse, it could pull any contamination lurking in your pipes into the city water system, e.g. legionella brewing in a not-hot-enough water heater. But keep in mind that loss of water pressure is a regular event in many cities in the world, such as Kharkiv, Zapohorizia, Odessa, Kryvyh Rih, Dnipro, Mikolaiv, Kyiv etc. — Harper - Reinstate Monica, Nov 05 '22 at 19:29
Yes, I told them. Unfortunately, they typically take about 3 weeks to answer, and then about 1 month to send someone to check. And then I expect that person to say it's my problem to fix. — DevShark, Nov 06 '22 at 07:55
So.... when service is disrupted your bill gets reduced somewhat. That seems fair to me. Why change it? — gnicko, Nov 06 '22 at 12:52
@gnicko my concern is that if air enters my system, I worry that it weakens the pipe and that eventually pipes will burst. I heard that having air instead of water is bad for the junctions. Also, when the water eventually reenters, I heard that the fact there is air increases the pressure in the system. — DevShark, Nov 06 '22 at 13:30
@Duston yes, I believe so. I have the picture in my post for the one-way valve I have in mind, which I believe is what you call a backflow preventer. Have you had any issue with it? Like water hammers? — DevShark, Nov 06 '22 at 13:34
@DevShark Air won't weaken the pipes. The outside of the pipes are surrounded by air all the time. Hammer arrestors actually make use of pockets of air to work. — gnicko, Nov 06 '22 at 13:39
@DevShark One of the things that seems concerning is why is your plumbing filling up with air when the water supply is interrupted? — gnicko, Nov 06 '22 at 13:54
@gnicko that's a great point. We heard air noises coming from 2 of the toilets. So my best guess right now is that these toilets flushes did not close well enough, and let air go through. — DevShark, Nov 06 '22 at 13:56
@DevShark Air getting in thru the toilets? The flush valves closing are significant to the sewer system at that point, not really water supply components. There really shouldn't be anywhere that would let large amounts of air into what's supposed to be a closed system. Stopping the air from getting in the supply pipes seems to be the objective here, not trapping the water in the system with a backflow valve. — gnicko, Nov 06 '22 at 14:03
@gnicko hmm, so during the water interruption, we noticed air noise coming from the toilet. We turned off the water tap that feeds the flush. The noise stopped. "Stopping the air from getting in the supply pipes seems to be the objective here" -> I understand your point. How important do you think this is? What downside is there in having air getting inside my supply pipes? — DevShark, Nov 06 '22 at 14:11

score 9 · Answer 1 · answered Nov 05 '22 at 16:41

9

You might start having problems with water hammer after installing a valve. If a valve* is turned off suddenly, it can cause a spike in pressure in the pipe behind it. Without a non-return valve, that pressure can dissipate out through your incoming supply.

Which means that you might need to install an expansion vessel after you have installed the valve.

*and that includes electric ones on washing machines and the like.

answered Nov 05 '22 at 16:41

Simon B

3,933
6
17

1

@DevShark Related problem is that any water heater may be dissipating pressure from heated water by allowing the cold water side to expand back through the incoming supply. If blocked, this could raise water pressure. To prevent this, it is standard to install an expansion tank on the cold water supply to any water heater. – Armand Nov 05 '22 at 18:37
@Armand thanks for your comment, that is a concern indeed. Just before the water heater, I have a pressure relief valve (see https://diy.stackexchange.com/questions/259793/water-leaving-the-house-when-water-cut-off). Do you still feel an expansion tank is necessary? – DevShark Nov 06 '22 at 13:40

score 7 · Answer 2 · answered Nov 05 '22 at 19:38

and then strong air pressure kept the water meter running

That wasn't air pressure. Where would the air even be coming from, unless you have a constant leak??? Or left a faucet wide open after discovering it was not flowing (which would be dumb).

More likely the air pressure was steam pressure from a tanked water heater having a meltdown, or simply gravity if the water in your system is above the water meter. Remember 30' (9m) of water height = 15 PSI = 1 bar = 100kPA of pressure.

I plan to buy a simple one-way valve... That seems pretty easy to do.

However, I am wondering if there's any downside to doing this? Could this somehow create damage to my system?

YES! What if your water system in your house becomes over-pressurized? I.E. pressure above intended? What happens?

Well, without a check valve it just pushes water out to the water mains, it's an annoyance but not a danger.

But with a check valve, nothing stops the water pressure in your house from going to infinity. Well obviously something will BREAK then, and we hope it's a pipe and not a violent BLEVE from your water heater.

So anytime you install a check valve, you must also install a pressure relief valve to vent any overpressure. I.E. the same thing that was happening through your water meter, only now it's dumping onto your property somewhere. It's perfectly allowed for this relief valve to dump into a sump or drain.

OP stated in a comment on linked question he already had a check valve on the tank. He did not see/remember it at first. — crip659, Nov 05 '22 at 23:04
Thanks Harper for your response. Indeed, I have actually a device just before the water tank, I believe it is a pressure relief valve (see https://diy.stackexchange.com/questions/259793/water-leaving-the-house-when-water-cut-off). — DevShark, Nov 06 '22 at 13:38
@DevShark often the device before the water tank is a check valve, and then the water tank has a pressure relief valve built into the tank as a safety feature. You'll need such a thing on the cold side too if you do that. — Harper - Reinstate Monica, Nov 06 '22 at 20:59

score 4 · Answer 3 · answered Nov 05 '22 at 17:59

4

The standard think is to install a check valve. I am sure it is code to have one installed but given you didn't even have a prv before I am not surprised you don't have one.

Mine looks like this:

answered Nov 05 '22 at 17:59

Fresh Codemonger

14,177
1
21
52

Commonly known in the US as a backflow preventer and typically installed just downstream of the main water cutoff. – Armand Nov 05 '22 at 18:53
1

What (in your mind) is the difference between a "check valve" and a "one way valve"? Without that information, this answer reads somewhat unhelpfully: "Q: I want to install a device that prevents water from going backwards. What should I know? A: Have you thought about installing a device that prevents water from going backwards?" – R.M. Nov 06 '22 at 16:58
1

Backflow preventers are generally double check valves to ensure that there is no contamination. Single check valves where you are preventing backflow of potable house water into potable city water carries less risk and doesn't require as strict of a device. My area requires yearly independent testing of backflow preventers used between an irrigation system and the city water hookup. No yearly testing of check valves is required. – Fresh Codemonger Nov 06 '22 at 17:57

score 2 · Answer 4 · answered Nov 06 '22 at 17:12

In the US, pressure relief valves that I have seen (like those on water heaters) are rarely-used safety devices - if they trigger, one would inspect to figure out what is wrong. The pressure ups and downs from normal working of a water heater on the other hand need a more nuanced regulation, which is where expansion tanks come in.

From thespruce.com:

In a closed plumbing system, a standard tank water heater can stress your plumbing pipes and fixtures through the normal thermal expansion that happens when water is heated. This can be a problem in any closed system where water is heated. Both water heaters and boilers for home heating systems can be prone to this kind of damage unless measures are taken to prevent it. With a plumbing system, a water heater expansion tank can help minimize the risk of pressure damage to the plumbing system. (This is normally not a problem on modern on-demand, tankless water heaters—only traditional tank-style heaters are subject to this problem.

It should be noted that all hot water boilers and hot water heaters have temperature and pressure relief valves. There are required by code and by law to prevent injury during abnormal pressure and temperature changes. They are automatic and will relieve water at the appliance, but an expansion tank is essential for the systems to operate within the design parameters.

...many homes have a closed water supply system that is equipped with a one-way valve such as a backflow valve, check valve, or pressure-reducing valve (PRV). In a closed system, this extra water pressure from thermal expansion is most likely to cause damage because the extra water pressure cannot push back into the city water supply and therefore has nowhere to go.

From an article on how to install an expansion tank for a water heater:

Inside an expansion tank is a flexible rubber diaphragm that divides the tank into two sections—one of which accepts expansion water as it heats, the other which provides an air chamber that becomes slightly pressurized as the diaphragm expands into it.

Any risk in installing a one-way valve?

4 Answers4