Expansion tank(s)?

[Gehrkmania]

Hi guys - we've had an issue for several years with pressure building in our water system, especially after the water heater has been taxed (after showers, running the dishwasher, washing machine, etc.). After any of those events, when we first turn on any faucet - you can feel a stiffness in the movement of the handle and for the first couple of seconds, the water pressure is very high.

I think we need to install 1 or maybe 2 expansion tanks to keep the pressure from building after we use hot water.

We have a 50 gallon gas water heater. Because I am wildly overconfident, I bought an expansion tank before I bothered to check the pressure. I bought one of these from Amazon: Watts DET-5 2.1 G Potable Water Expansion Tank for 50-Gallon Water Heaters. It says it has a max pressure rating of 150 psi.

I just bought a pressure gauge and took some readings:
Street (taken at outside hose spigot nearest to the street) = 120 psi.
Inside, after pressure reducing valve (taken at washing machine cold water connection) - static pressure ~ 45 psi
Inside, same location after sitting overnight and having run dishwasher = 120 psi


I don't think we have a backflow preventer, so my assumption is that once the inside pressure goes above 120 psi, it's just pushing back into the line from the street and never rises above 120.

Is it as simple as adjusting the pressure in the expansion tank to match the static pressure in our system (~45psi), and then the tank will be able to absorb that extra 75 psi when the water heater gets in on the action?

Also - from what I've read, it sounds like we ought to be able to open up the pressure reducing valve a little and safely increase our static pressure by 15 or 20 psi. If that's the case, would there be any reason not to do that?

Thanks for your help!

 

[journeyman]

your expansion tank should be set to the same pressure has your house pressure. if you have 65 psi after reg your tank should be set at 65 psi. as long as you dont have plastic water lines in house your pressure should be 65 psi. you will loose about 5 psi when a faucet is turned on. check to make sure your reg is working properly by doing a running test. if pressure drops 10-15 psi the reg is bad. a running test is the proper way to test a reg.

 

[Leafzfan]

your expansion tank should be set to the same pressure has your house pressure. if you have 65 psi after reg your tank should be set at 65 psi. as long as you dont have plastic water lines in house your pressure should be 65 psi. you will loose about 5 psi when a faucet is turned on. check to make sure your reg is working properly by doing a running test. if pressure drops 10-15 psi the reg is bad. a running test is the proper way to test a reg.

Hi journeyman, just curious why you say "as long as you don't have plastic waterlines in the house"

 

[Leafzfan]

No disrespect intended, thanks

 

[phishfood]

He likes him some copper.

I don't mind copper, as long as the water is good.

 

[journeyman]

hi pressure will increase potential leaks mostly referring to quest pipe phish and for the record i like the way pex is installed just always been a copper fan but thats why i like you phish because we can compare knowledge to make us better plumbers

 

[Gehrkmania]

'Sup guys? It's been a couple of years and we've still been experiencing the original issues described above.

Since the initial post, I've replaced the expansion tank again with a larger model (Amtrol ST-12), hoping that the system just needed a tank with more volume.

When I replaced the expansion tank, I measured the water pressure at the water heater drain at ~ 50 lbs. I set the new expansion tank at 50 lbs and installed it.

I left the pressure gauge on overnight and this morning, it's reading nearly 120 lbs again.

Clearly, I'm doing something wrong. What details can I provide that would help get this sorted out?

Thank you!

 

[breplum]

I am pretty convinced that you have a defective PRV. I have seen this kind of pressure creep many times (42 years experience).
I have used repair kits for various PRVs, both Watts and Wilkins, and will say now that I don't bother with repair kits any more because for one reason or another, the kits fail to fix the defective PRV.
And we now always use PRVs with double unions, to make swapping out a breeze.

 

[Gehrkmania]

Do you have any recommendations for a new PRV? Lowes and Home Depot are close to home, but I could also order one off the interwebs if there's a model you really like.

Thank you!