Pressure reducing valve advice

[CallmeJake]

I moved into a new house last spring. When we were planning for the sprinkler system I measured the water pressure at the bib at a little over 80psi at the hose bib.

What I noticed over the summer is that when the sprinklers would turn off it would occasionally trip the pressure valve on the tankless heater. Also, when I was flushing the radiant loop in the basement floor if I closed the fill valve too fast the water heater valve would blow off.

Because of those issues and the high pressure to the house in general I have been considering installing a PRV for the house. I am hesitant to add another thing that requires maintenance though.
A few questions I am hoping for help with:
1. Would a PRV help with the issues I have described?
2. Could this just be an issue with the pressure valve on the heater? I am not sure how to test this without pressurizing the whole system to 125psi. It seems to be fine with other loads like the washing machine/dishwasher/ice maker.
3. Would an expansion tank on the mainline help, do they act like a water hammer arrestor for the whole house? I believe one would be required if I install the valve anyway, is that right?

I appreciate any help.

 

[James Henry]

If the water pressure entering your house is over 65-70 PSI. you need to install a PRV. Just after your main supply shut off I would install a strainer and then a PRV.

 

[Sponsor]

 

[Reach4]

Get a garden hose thread pressure gauge, or find your old one. Even with a tankless WH, I suspect there would be some thermal expansion right after a shower. So with that, is the pressure rise just a pulse, or was it over a longer period. You can put one on a laundry tap, for one place.

Would an expansion tank on the mainline help, do they act like a water hammer arrestor for the whole house? I believe one would be required if I install the valve anyway, is that right?

I would consider the thermal expansion tank. I don't know anybody with a PRV, tho they appear to be increasingly used in more and more areas. If I had a solution that did not involve a PRV, I would try that.

 

[James Henry]

I have never heard of a " Whole house expansion tank " unless you consider an expansion tank on a water heater a whole house expansion tank. an expansion tank is installed on a water heater to compensate for the expansion of water when the temperature is increased and when their is a check valve on the water meter which keeps the water from creeping back into the water service main thus relieving the pressure on your distribution lines. A water hammer arrestor is installed near quick closing valves to absorb the shock of the water being shut off suddenly, i.e. flushometers, metering faucets, the arrester is supposed to be installed as close to that valve as possible. 80 PSI is not recommended for residential supply lines because it puts stress on the lines. 65-70 PSI is best.

 

[CallmeJake]

Thanks guys.

When the PRV is installed is an expansion tank down stream necessary? James mentioned when there is a check valve in the water meter, for example, a tank would be required. Is turning the pressure down 10psi enough to stop the water heater valve from popping when the sprinkler valves close?

What I was getting at with the expansion tank acting as a hammer arrestor was that the blow off pops only when a valve is closed quickly. In other places where there are quick closing valves water hammers arrestors are installed. I was asking if an expansion tank would absorb some of the pressure shock that is causing the water heater pressure valve to open since it's purpose is to absorb excess pressure from hot water expansion.


Reach4, I am not sure I am following your question. All winter I have not had a problem with the valve opening after showers or otherwise, makes me think it has more to too with the pressure spike after a valve closes rather than excess pressure from the tankless. In any event I'll look for a place to attach the hose thread gauge, I don't have laundry tub but I think the tankless has a place I can attach it.

 

[James Henry]

Thanks guys.

When the PRV is installed is an expansion tank down stream necessary? James mentioned when there is a check valve in the water meter, for example, a tank would be required. Is turning the pressure down 10psi enough to stop the water heater valve from popping when the sprinkler valves close?

What I was getting at with the expansion tank acting as a hammer arrestor was that the blow off pops only when a valve is closed quickly. In other places where there are quick closing valves water hammers arrestors are installed. I was asking if an expansion tank would absorb some of the pressure shock that is causing the water heater pressure valve to open since it's purpose is to absorb excess pressure from hot water expansion.


Reach4, I am not sure I am following your question. All winter I have not had a problem with the valve opening after showers or otherwise, makes me think it has more to too with the pressure spike after a valve closes rather than excess pressure from the tankless. In any event I'll look for a place to attach the hose thread gauge, I don't have laundry tub but I think the tankless has a place I can attach it.

1. I would replace the relief valve first, it may have some dirt in it causing it to pop off easy.
2. I would install a PRV, 80 PSI is high and it may even fluctuate higher which might explain the occasional pop off. If you install a PRV you will need to install an expansion tank.
3. check and see if you have a check valve on your water meter, if you do you need an expansion tank.

 

[Themp]

https://homeinspectioninsider.com/tankless-water-heater-expansion-tank/

 

[Jeff H Young]

80 psi is high and right about where a regulator begins being required. a long water service combined with minimal sized piping adds to creating pressure drop so when water valve closes a hammer occurs spitting water from relief valve a weak, or defective relief valve causes or contributes as well. its not rare to have a bad t and p valve 15 or 20 bucks concider changing. installing a pressure reducing valve is a good idea as well with 80 psi being the max .

 

[PlumbNuts]

You stated that it was 80 psi, that was the pressure at the time that you observed it; how much more does it possibally increase during non-peak usage hours?
Yes, a PRV is a good idea. It will reduce the pressure on your entire plumbing system and help decrease wear which over time saves you money.
Yes, if you do not have a thermal expansion tank then you should have one installed; although it is designed for thermal expansion it does in a small way act "like" a water hammer arrestor for your entire home.
If your T&P valve on your water heater has been tripped multiple times then you may need to have it replaced.

I don't know about prices in your area but here I know that I could do all 3 of those for under $1000.00 so you are not really looking at a major investment and in the long run could save you that amount.

 

[CallmeJake]

It looks nearly unanimous that a PRV should be installed, I am going to start looking into that.

For the tank it sounds like it may not be required from a code perspective but it could help and won't hurt. Since the lines have to be drained for the PRV might as well install that and and a new water heater valve at the time.

 

[Reach4]

So in your proposal, would the tee to the irrigation be upstream or downstream of the PRV? Many like the higher pressure for irrigation.

If you decide to get a PRV, there is a list of things to deal with.

For the tank it sounds like it may not be required from a code perspective but it could help and won't hurt.

What tank? I might opt for something like a WX-102 or WX-103 on the same side of the irrigation. That would be like a big water hammer arrestor, and may double for thermal expansion, depending on stuff.

Will you have a separate thermal expansion tank, or will you use a bypass type PRV with a tank upstream of the PRV?

Will you install a filter before the PRV? Many have a built-in filter.

If you put in a PRV, I would have a way to measure pressure on each side.

PRVs can fail. Will there be any provision to make repair or replacement easier?

 

[CallmeJake]

Thanks for pointing out some of the details. My plan after some quick thought is below, open to suggestions.

I would have the irrigation downstream of the PRV. The sprinkler design was done assuming a pressure of 70psi, instead of the 80+ I measured, with the idea of bringing the pressure down.

My thought is something like this:
meter->existing ball valve->wye strainer-->PRV--> isolation valve->somewhere downstream->tee->valve->expansion tank

If I understand correctly, I could use PRV with or without a bypass in this case because the expansion tank is downstream of the PRV.

Gauges are a good idea, I have a couple of spare tridicator's I could put in. Would also tell me how cold the water gets.

I just looked at those tanks, is there a reason you would use a well tank over a similar sized potable water tank like the PLT-5? Any experience with flow through tanks?

 

[Reach4]

I would have the irrigation downstream of the PRV. The sprinkler design was done assuming a pressure of 70psi, instead of the 80+ I measured, with the idea of bringing the pressure down.

Look at the curves on your prospective PRV. How much pressure drop do you get at say 10 gpm? What is the minimum differential? Can you put 80 psi in and get close enough 70 psi out over a range of flows?

 

[CallmeJake]

I had to do a little reading on this. The line into the house is 1" copper, plan is to keep the PRV at line size.

For the valve I am looking at the watts 1" LFU5B-Z3, it is a bypass type with integrated strainer.

If I am understanding the table correctly, with 80 in and a 70psi set point this valve can stay above 65 psi for flows up to around 9 GPM, and above 60psi to 20GPM.

That should work for the irrigation at the higher flow rate and still keep the pressure up for showers and such. Seems reasonable?

Back to the tanks, any reason to use a well tank vs something less expensive?

 

[Reach4]

Back to the tanks, any reason to use a well tank vs something less expensive?

Not sure. Well tanks are normally precharged to just under the minimum pressure, and thermal expansion tanks are normally charged at, to a little over, the PRV setting.

Is the construction of a well pressure tank better in some way than a thermal expansion tank? I don't know. Thermal expansion tanks usually have 3/4 inch threads and small pressure tanks have 1 inch threads. I am not thinking that is a deal maker/breaker.

 

[Fitter30]

Ex tanks with prv is a have to be installed on the downstream side of the valve on the cold water line. Normally install with brass screwed fittings enter side of the water heater and tank air pressure should be set at water pressure.
Ex tank has only one job take care of hot water expansion nothing else.
A 40 gallon water heater with 80 PSI line pressure will build to a pressure of 145 PSI with a temperature increase of 16°F. (Brandford White 2019)

 

[Jeff H Young]

I don't put well tanks on city water . I didn't check but tank might not be needed at all with a tankless heater.
I notice around here many times the irrigation is not reduced pressure and sometimes there are 2 PRV one on house and one on irrigation though far less common.
Recently on a PRV install I put a tee on both sides of PRV to allow customer and irrigation contractor decide which tee to use sprinklers had been disconnected and needed work.

 

[Reach4]

The symptom that the OP had was a water spike when the irrigation shut off. So the thought was that something near the irrigation valve could act as a water hammer arrester, pressure spike arrester and a thermal expansion tank all in one.

There was no high-pressure complaint, other than the pressure spike dribbling water out of the tankless WH T&P valve , other that wondering if a PRV would kill the pressure spike.

I would try a tank at about the tee to the irrigation, and nothing more. Yes, leave space for a potential future PRV.

 

[PlumbNuts]

The symptom that the OP had was a water spike when the irrigation shut off.

He also said:

Also, when I was flushing the radiant loop in the basement floor if I closed the fill valve too fast the water heater valve would blow off.

If there is not an expansion tank at the water heater then that is where it should be,

There was no high-pressure complaint,

I measured the water pressure at the bib at a little over 80psi at the hose bib.

80 psi is high pressure on a home, a PRV will regulate the pressure between 45-75 psi; an optimal pressure would be around 55 psi.

Depending upon jurisdictional codes once a PRV is installed it will create a closed loop which will require a thermal expansion tank.

 

[Reach4]

If there is not an expansion tank at the water heater then that is where it should be,

We can disagree on that. A tank near the irrigation tee would be similar to a well with a pressure tank. Would you propose that somebody with a well and pressure tank also have a thermal at the WH -- presuming no check valve is between the pressure tank and the WH?

80 psi is high pressure on a home, a PRV will regulate the pressure between 45-75 psi;

You have experience with PRVs, and I don't have any. I think them as a potential PITA maintenance/failure thing.