Softener, PRV, Expansion Tank

SG17

New water softener 3 months ago and water hammer began after one month of use and after putting softener in bypass the first time. Softener company replaced entire system and nothing changed. They said it was unrelated to the softener. Called a plumber out and he said the PRV was failing. He put a new one on. The house is under 3 years old and this is its 3rd PRV. We had to change one last year when our pressure began reading 120psi suddenly. This time we had seen no indication of failure, but went along and had a higher quality PRV installed. After 2 days the "thud" sounds in the wall returned whenever flushing or turning off a faucet. We had the plumber come out again and he said the expansion tank was bad. You could definitely feel the "thud" in the tank. Thankfully that seemed to be the fix for the hammer, but now it seems that every time the water heater heats the pressure gauge built into the softener shoots up from the 57 setting to 70 psi. I can barely open a faucet or flush a toilet and it drops back down to 57. What is going on? Is this normal?? I am concerned if it would continue rising if no water were used...

Jamie Hall

It probably is normal -- it depends entirely on the acceptance volume of the expansion tank relative to the volume of the water heater. In your case, I'm guessing that the expansion tank is the cute little thing teed off the water heater. That will tend to reduce water hammer, particularly in the lines connected directly to it, but it's much too small to control pressure variations caused by temperature changes in that big water heater.

SG17

I guess I am confused why I wasn't seeing these fluctuations before the new tank. The old expansion tank was exactly the same size and brand. It had been installed horizontally which the plumber thought had initiated the failure. I'm just concerned about continued pressure building. I'm just unsure if I need to call them back out or not. Maybe this is typical for my current setup. 🤔 

leonz

You need to know what the pressure is in the expansion tank WITH THE WATER DRAINED
out of the bladder tank, a lower air pressure will allow for more compression of the air in the
expansion tank with a greater acceptance volume and a quieter potable water supply.

They should have installed a shut off/drain valve under the bladder tank also.

Intplm.

Was the gauge there before all of this started?
Pressure can and does fluctuate differently under many different circumstances. You might be experiencing "normal" occurrences.

SG17

Yes. The gauge has been there since the softener was installed 3 months ago. It is built into the softener system. I don't hear any sounds from anything. I don't even hear when the water heater is in heat cycle, just guessing since after a large use if hot water is mostly when I see the psi rise. Just seeing the fluctuation. Everything seems to be normal with pressure at any fixture in the house. I just can't see why it would have solved the hammer but started the fluctuations. 

ChrisJ

If the PRV failed after 3 years I'd put a really good strainer ahead of it to catch any garbage that may get stuck in it or damage it. Something with a good 80 or 100 mesh strainer in it. Most brass and bronze strainers come with a 20 mesh, but they usually have an option for the finer 80 ones.

I know it's a separate subject, but figured I'd mention it.

As far as 70 and dropping to the high 50s, that's likely very normal due to how the PRV operates. You're going to have a small range in pressure as the valve needs this drop in order to open further. I wouldn't be surprised if it drops to the low 50s under heavy flow.

SG17

So if it gets up to 70 after heating, and say I were not to be home using any water for a couple of days, it won't just keep rising on top of that will it? I'm guessing it drops even if I don't open a faucet or flush? Sorry, I'm paranoid about this. I look at it 20 times a day. 

ChrisJ

SG17 said:

So if it gets up to 70 after heating, and say I were not to be home using any water for a couple of days, it won't just keep rising on top of that will it? I'm guessing it drops even if I don't open a faucet or flush? Sorry, I'm paranoid about this. I look at it 20 times a day. 

Wait I just re-read your original post.

You're 100% that the pressure goes up from the water heater?

I assumed you meant it was 70PSI with nothing running, and 57 PSI with stuff using water.

hot_rod

Check the incoming pressure. PRV want a 2:1 maybe 3:1 pressure reduction. If main pressure is over 150, psi two PRVs in series 

High incoming or spikes destroy PRVs

A water  hammer arrester at the softener may be  a good add on

SG17

I assume the water heater. It is set at 57. Drops to 50 when using water and will go to 70 seemingly after a lot of hot water has been used or a couple of random times throughout the day. I literally can barely open a faucet for 2 seconds and it drops back to 57. I don't hear the water heating so I can't be sure, but it seems to be from that based on the timing.

SG17

I have tried a 2 hand gauge on an outdoor spigot. The black hand was always at 57 when the softener gauge was at 57. The red hand would go from 80-120 max, but I can't be sure how accurate it was. I never saw the black hand change. Ugh....

hot_rod

45- 60 psi is plenty for a home. Plumbing fixtures are rated to max. 80 psi.

The pressure you measure with nothing running in the home is static pressure, set the PRV to 60 with nothing running.

The pressure as you start flowing things, dynamic pressure, will drop. This is called fall off pressure.
Ideally with everything in the home running a 7- 10 psi fall off is rule of thumb. If it drops 10 psi with one fixture running, a plugged strainer, valve not completely open, failed prv. Or some other obstruction in the main piping.

Pressure creep is either lack of working thermal expansion device, or a PRV leaking by.

SG17

Thanks everyone for your insight. Going to call the plumber to come back.

retiredguy

My sons incoming water pressure is at 100 -120 PSI so he and I installed a name brand and expensive PRV on the supply line and set the discharge pressure at 65PSI. We also installed a water hammer arrester near that PRV in the same horizontal line. We installed an oversized expansion tank at the water heater with the air charge at 60 PSI. His PRV is now over 10 years old and working fine. The water pressure fluctuates by 5-10 PSI depending on the demand. He has never seen the system pressure exceed 70 PSI.

SG17

Thanks for the info. This morning my gauge read 70. Turned on a faucet and it dropped to about 48, then rose to 56. It soon returned to 70 and then dropped to 66 about an hour later with no water having been used. I'm so perplexed by this. If the new PRV and new ET are set to 58ish I just assumed it would stay there when no water is being used. My old PRV and ET were not fluctuating, I just had suddenly got hammer in expansion tank. I'm so reluctant to call them back. The items they installed have 5 years warranty through them. I'm just concerned they will tell me it's another faulty item needing replaced in a house under 3 years old. 3 PRVs and 2 ETs in that amount of time already seems hard to process. 

SG17

Is it possible they have set the expansion tank at a higher psi allowing the pressure to rise to 70 even though the PRV is at 58?

ChrisJ

SG17 said:

Is it possible they have set the expansion tank at a higher psi allowing the pressure to rise to 70 even though the PRV is at 58?

My first guess was they didn't properly precharge the tank so it's waterlogged and not doing it's job, much.

Also, what size water heater is that? It looks rather large.

SG17

The water heater is 50 gallon. The expansion tank definitely sounds hollow when knocking at the top vs the bottom. I know they added air with a pump to the tank when they put it on but I never  asked any questions regarding the psi. I had not mentioned, though it seems irrelevant, all the copper plumbing in the photos was installed with the new tank. It had braided flex and pex before.  For a girl, I'm having to try way too hard to figure this out. Don't have a lot of plumbing knowledge and I'm concerned that's putting me at a huge disadvantage. I don't feel like the fluctuations are hurting anything I just don't feel like it should be performing this way.

EBEBRATT-Ed

I agree with @ChrisJ . The plumber needs to remove the expansion tank or isolate and drain it then and only then check the air pressure in the tank.

The air pressure in the tank should then be adjusted to see the same pressure the prv puts out and a gauge should be installed on the system. The reinstall the tank with the adjusted pressure.

SuperJ

You could probably shut power and water off to the tank.  Drain a little water to get to 0psi and set the bladder pressure.  

Ideally the tank should have a valve setup to isolate it and allow pressure to be released.  It should be checked annually. 

The bladder needs to be set with enough pressure to balance the water pressure at setpoint.  So it has some headroom to collapse progressively as the pressure goes above setpoint.  If the pressure is not high enough it may be have compressed at setpoint leaving little room to account for thermal expansion or regulator fluctuations. If the bladder is collapsed a small amount of expansion can cause a big pressure change since there is no where for the added volume to go but to slightly expand/stretch anything that gives. 

Also agree on adding a strainer upstream of the regulator. 

Some tanks like to be oriented different directions depending on the style of bladder. And will last longer in the recommended orientation. 

Jamie Hall

Ah... very helpful. Besides the pressure tank, you mention in passing that " all the copper plumbing in the photos was installed with the new tank. It had braided flex and pex before". A useful object lesson in never overlooking anything that changed between when it worked and when it didn't. That flex and pex was absorbing a lot of the water hammer and pressure change -- quite possibly all of it -- and the copper can't.

ChrisJ

Jamie Hall said:

Ah... very helpful. Besides the pressure tank, you mention in passing that " all the copper plumbing in the photos was installed with the new tank. It had braided flex and pex before". A useful object lesson in never overlooking anything that changed between when it worked and when it didn't. That flex and pex was absorbing a lot of the water hammer and pressure change -- quite possibly all of it -- and the copper can't.

No,
But that expansion tank should be absorbing a lot of it, off the top of my head that tank is more than big enough for a 50 gallon heater.

SG17

I confirmed today that the rise is definitely happening when the WH heats and it does return to the set psi after it cools. One person had suggested this may be normal.  I feel like the plumber should have mentioned if this was something I would see happening. Won't be able to have them come back for a week or two. Just gate to pay another trip fee. I'm already $$$$ in on this.

ChrisJ

SG17 said:

I confirmed today that the rise is definitely happening when the WH heats and it does return to the set psi after it cools. One person had suggested this may be normal.  I feel like the plumber should have mentioned if this was something I would see happening. Won't be able to have them come back for a week or two. Just gate to pay another trip fee. I'm already $$$$ in on this.

I'm not sure if I had suggested it or not, but no, I don't feel that's normal with a properly working expansion tank.

Jamie Hall

ChrisJ said:

SG17 said:

I confirmed today that the rise is definitely happening when the WH heats and it does return to the set psi after it cools. One person had suggested this may be normal.  I feel like the plumber should have mentioned if this was something I would see happening. Won't be able to have them come back for a week or two. Just gate to pay another trip fee. I'm already $$$$ in on this.

I'm not sure if I had suggested it or not, but no, I don't feel that's normal with a properly working expansion tank.

Too many variables, @ChrisJ . The pressure will always rise in a closed system when the water is heated. The question is... how much, and how much is "normal". It depends on the total volume of the water being heated, the initial and final temperatures, the initial pressure, the expansion volume available in the tank and the air pressure in the tank at the start... water heaters (as contrasted with boilers) are problematic, as there is a comparatively large volume of water involved, the delta T is large, and the initial pressure is usually rather high again compared to a boiler. All of which mean that a surprisingly large tank is required to keep the pressure change small.

ChrisJ

Jamie Hall said:

ChrisJ said:

SG17 said:

I confirmed today that the rise is definitely happening when the WH heats and it does return to the set psi after it cools. One person had suggested this may be normal.  I feel like the plumber should have mentioned if this was something I would see happening. Won't be able to have them come back for a week or two. Just gate to pay another trip fee. I'm already $$$$ in on this.

I'm not sure if I had suggested it or not, but no, I don't feel that's normal with a properly working expansion tank.

Too many variables, @ChrisJ . The pressure will always rise in a closed system when the water is heated. The question is... how much, and how much is "normal". It depends on the total volume of the water being heated, the initial and final temperatures, the initial pressure, the expansion volume available in the tank and the air pressure in the tank at the start... water heaters (as contrasted with boilers) are problematic, as there is a comparatively large volume of water involved, the delta T is large, and the initial pressure is usually rather high again compared to a boiler. All of which mean that a surprisingly large tank is required to keep the pressure change small.

So.
How do we calculate how much 50 gallons (extreme situation) will expand when heated from 40F to 140F?

WMno57

The expansion tank is on the cold side of the water heater. Is there a heat trapping nipple or check valve on the cold inlet?

ChrisJ

WMno57 said:

The expansion tank is on the cold side of the water heater. Is there a heat trapping nipple or check valve on the cold inlet?

You wouldn't think so from the factory as most of them rely on the city water (without PRV etc) or well tank for expansion purposes.

Though, now that you mention it, it looks like they did use dielectric unions which isn't necessary on a Bradford White and in my opinion, would likely cause more issues than they solve. But that's a totally different subject.

hot_rod

ChrisJ said:

Jamie Hall said:

ChrisJ said:

SG17 said:

I confirmed today that the rise is definitely happening when the WH heats and it does return to the set psi after it cools. One person had suggested this may be normal.  I feel like the plumber should have mentioned if this was something I would see happening. Won't be able to have them come back for a week or two. Just gate to pay another trip fee. I'm already $$$$ in on this.

I'm not sure if I had suggested it or not, but no, I don't feel that's normal with a properly working expansion tank.

Too many variables, @ChrisJ . The pressure will always rise in a closed system when the water is heated. The question is... how much, and how much is "normal". It depends on the total volume of the water being heated, the initial and final temperatures, the initial pressure, the expansion volume available in the tank and the air pressure in the tank at the start... water heaters (as contrasted with boilers) are problematic, as there is a comparatively large volume of water involved, the delta T is large, and the initial pressure is usually rather high again compared to a boiler. All of which mean that a surprisingly large tank is required to keep the pressure change small.

So.
How do we calculate how much 50 gallons (extreme situation) will expand when heated from 40F to 140F?

Use the Amtrol Net Expansion of Water tables 40- 180° the factor is .02763 X 50= 1.38

Jamie Hall

ChrisJ said:

Jamie Hall said:

ChrisJ said:

SG17 said:

I confirmed today that the rise is definitely happening when the WH heats and it does return to the set psi after it cools. One person had suggested this may be normal.  I feel like the plumber should have mentioned if this was something I would see happening. Won't be able to have them come back for a week or two. Just gate to pay another trip fee. I'm already $$$$ in on this.

I'm not sure if I had suggested it or not, but no, I don't feel that's normal with a properly working expansion tank.

Too many variables, @ChrisJ . The pressure will always rise in a closed system when the water is heated. The question is... how much, and how much is "normal". It depends on the total volume of the water being heated, the initial and final temperatures, the initial pressure, the expansion volume available in the tank and the air pressure in the tank at the start... water heaters (as contrasted with boilers) are problematic, as there is a comparatively large volume of water involved, the delta T is large, and the initial pressure is usually rather high again compared to a boiler. All of which mean that a surprisingly large tank is required to keep the pressure change small.

So.
How do we calculate how much 50 gallons (extreme situation) will expand when heated from 40F to 140F?

The coefficient of expansion of water is variable, but 0.0005 is a good first approximation. So, in your instance, it would be about 2.5 galloons.

hot_rod

ChrisJ said:

WMno57 said:

The expansion tank is on the cold side of the water heater. Is there a heat trapping nipple or check valve on the cold inlet?

You wouldn't think so from the factory as most of them rely on the city water (without PRV etc) or well tank for expansion purposes.

Though, now that you mention it, it looks like they did use dielectric unions which isn't necessary on a Bradford White and in my opinion, would likely cause more issues than they solve. But that's a totally different subject.

Most tanks have heat trapper nipples, either a rubber flapper or plastic ball inside. I don't think they are a "bubble tight" seal, so the pressure would bleed through to the tank. I can blow through this one, the flapper is a bit smaller than the ID of the nipple.

Jamie Hall

Oops. Read the wrong value for expansion -- that's the Celsius value. The Fahrenheit value is 0.0003, the volume is 1.5 gallons. Still a fair amount.