PRV, Expansion Tank, pressure gauge question

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JoeSD

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My plumber replaced my expansion tank since the old one had failed, the PRV is at 60 PSI and the plumber set the new expansion tank to 65 PSI. I have a pressure gauge attached to the hose spigot next to the cutoff outside monitoring the pressure and it stays at 60 PSI throughout the day while we're at home, overnight I noticed it had crept up to 65 and stayed there until I took a shower then back down to 60. Does that mean everything is working correctly? Since the expansion tank is set to 65 PSI that's why the gauge maxed out at 65 overnight?
 

breplum

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For Watts brand tanks, precharge pressure is supposed to be set at house static pressure.
It is probably ok set where it is if that rangy static pressure gets to 65.
The precharge pressure will not prevent overpressure but mitigates the effect as water heats and expands.
 

JoeSD

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Do you think should I try and lower the expansion tank PSI to 60 or just leave it alone? I looked at the tank, it is a PFXT5 from Proflo.
 
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JoeSD

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So now the black needle on the pressure gauge is climbing to 70 PSI overnight/when we're out of the house for a few hours when the water heating is heating up. Is the expansion tank getting overwhelmed since it wasn't set to 60 PSI (same as the PRV) ?
 

Reach4

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So now the black needle on the pressure gauge is climbing to 70 PSI overnight/when we're out of the house for a few hours when the water heating is heating up. Is the expansion tank getting overwhelmed since it wasn't set to 60 PSI (same as the PRV) ?
There is a often a check valve in the system, and the only place for the expansion to go is the expansion tank.

With your precharge at 65 instead of 60, close enough. If you leave it, that precharge will drop to 60 at some point, maybe a few years. Air diffuses through the diaphragm. I think you are supposed to check the precharge annually. Precharge is read with the water pressure at zero.

Don't worry about the pressure rising to even 120 or 130 right after using a lot of hot water and you stop using any water. One person argues against that. What you don't want is for the pressure to get close to where the safety temperature and pressure gauge routinely drips water.

But anyway, if you had a peak reading pressure gauge you would see the peak is going to be more than 70. Try starting taking a movie of that gauge as you take a long hot shower. Then turn off the water, and don't use a faucet or flush a toilet. Don't have the ice maker fill. By the time the WH turns off after recovering to its setting, you will see the pressure was higher.
 

JoeSD

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What you don't want is for the pressure to get close to where the safety temperature and pressure gauge routinely drips water.

Would our master shower dripping a little bit of water randomly throughout the day sometimes be related to that?
 

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Would our master shower dripping a little bit of water randomly throughout the day sometimes be related to that?
Yes, in two ways that I can think of. One would be that the leaky valve drip prevents the pressure from rising a normal amount.

If we imagine that 110 psi causes your shower to drip, that could also be related. But showers, especially those with handheld showers, sometimes drip at odd times.
 

JoeSD

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Thank you for all the helpful info! With all the information I listed in this thread, do you think I should be good to go?
 

jadnashua

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The size of the ET will make a difference in how much the pressure rises, but since the water incompressible, with the ET precharge set higher than your static pressure, as soon as any expansion starts, it will immediately jump to 65-psi, your precharge value. Then, depending on how much expansion you get, the pressure will rise still…the bladder in the ET only compresses as the water expands, but that expansion of the water is compressing the bladder (balloon) into a smaller space, which means that it’s pressure must rise, too. The larger the ET, the smaller the percentage of the air is compressed for whatever expansion occurs in the water.

The reason it immediately drops to your PRV setting is, the water stored in the ET gets pushed out since it’s pressure is higher than your supply when you open a valve. If you have a slow leak anywhere, the pressure would slowly bleed off. The fact that it goes up indicates you don’t have a leak, which is a good thing!

So, since the amount of expansion depends on the volume of the WH you’re reheating, and when in the cycle of use, say using most of the tank, then stopping water use would create the largest volume, and thus, the largest pressure rise. Washing your hands or maybe a load of dishes in the DW won’t use anywhere near as much hot water as the average person’s shower, and some will empty their WH, which will lead to the worst case.

FWIW, the only ‘cost’ to a larger ET is a small incremental cost to buy it, and the support and size of it when installing it in prep for when it fails the next time…larger tank, larger volume, less pressure rise, more weight to hold up without stressing the plumbing.
 

JoeSD

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In the last few days I've noticed the pressure gauge (I never took it off the hose spigot next to the cutoff) measures a constant 65 PSI now instead of 60 PSI. I haven't touched anything since last month when I made this post. Is that a bad sign that the PRV is starting to fail?
 

jadnashua

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It may just mean that things are settling down...I'd readjust it to where you want, then see if it stays. There's a spring and seals in there. It's also possible that you may have some debris in your water (like sand particles), that are messing with the seals. There's an inlet filter screen that traps most of that sort of stuff, but not necessarily all. If you didn't tighten the lock nut well, the adjustment shaft may have shifted.
 

Jeff H Young

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In the last few days I've noticed the pressure gauge (I never took it off the hose spigot next to the cutoff) measures a constant 65 PSI now instead of 60 PSI. I haven't touched anything since last month when I made this post. Is that a bad sign that the PRV is starting to fail?

I wouldn't worry about it. of course everything is starting to fail the day you install it. but there could be some breaking in of it I suppose. so re set it to 60 if you wish, but as long as pressure doesn't continue creeping up no problem.
 

JoeSD

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It may just mean that things are settling down...I'd readjust it to where you want, then see if it stays. There's a spring and seals in there. It's also possible that you may have some debris in your water (like sand particles), that are messing with the seals. There's an inlet filter screen that traps most of that sort of stuff, but not necessarily all. If you didn't tighten the lock nut well, the adjustment shaft may have shifted.

I checked the lock nut and it was loose and turnable by hand. I tightened it down. We are also in the middle of a heat wave. Is there such a thing as the city water supply heating up and increasing PSI by a few degrees?
 

Reach4

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I checked the lock nut and it was loose and turnable by hand. I tightened it down. We are also in the middle of a heat wave. Is there such a thing as the city water supply heating up and increasing PSI by a few degrees?
I am going to say no, but city water pressure can change. One of the changes is if people are using less water, the pressure at your house for the input of the PRV can increase. Maybe during a work day it will drop some.
 

jadnashua

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It's not uncommon for the utility to need to raise pressure at night to refill any water towers. A well-functioning PRV should keep the pressure fairly constant, but might drift a little bit. It can drop a little bit in the morning while everyone is getting ready for school or work and the demand is higher as well. That's why when checking pressure, it's a good idea to use a gauge with a second, tattle-tale hand to show you peak pressure. I've not seen one, but they may make one with a min/max set of hands on it, too.
 

JoeSD

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Mine has a black hand and a red hand for peak pressure. The red hand sometimes gets to 80 overnight but not above that since the new tank has been installed. I've been watching and adjusting the PRV all week and still can't tell if it's faulty or starting to fail. Very frustrating!
 

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80 overnight is nothing to worry about. Even 120 peak would probably be due to thermal expansion, and would not be a worry after using a lot of hot water IMO.

If the PRV is leaking, expect pressure rises even when you did not heat water.
 

jadnashua

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The size of the ET, the temperature rise, and the size of the WH tank will determine how high the pressure will rise. The larger the ET, the less rise. The lower the temperature rise, the less rise. The smaller the WH, the less rise. The goal is to keep it stable, and not, ideally, rise above the nominal 80psi max defined for domestic water supplies. Oversizing the ET will keep the pressure differential smaller, and because it won't flex as much, should increase its longevity, thus, likely overcoming the slight increase in price for a larger one.
 

JoeSD

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An update to my never ending expansion tank and PRV saga. The plumber replaced the ET in August and it was bad as I suspected. Then last month the PRV started having pressure go all over the place and leaking rust colored water out of it, so the plumber replaced it with a nice new all brass unit. After that I noticed the pressure was getting up to 100 overnight or when the WH would run, I suspected something was up with the new ET. The PRV is set at 67.5 PSI, so I turned the water off to the house and opened a faucet until the water stopped coming out, then I used my digital air compressor and checked the expansion tank and it was down to 29 PSI. I refilled it to 68.5 PSI and then turned the water back on.

Did I do it right? Why would a new ET go down to 29 PSI so soon?
 
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