Pressure phenomena question?

[Vitaliy]

Hi,

Two days ago I installed 36 series Conbraco pressure regulator to reduce
city water pressure from 90+psi down to 50psi. I also installed two pressure
gauges before and after the regulator. Regulator seems to be working fine
but I have noticed very strange pressure phenomena, already happened 3-4
times. After water was used for a wile and then all faucets where closed
(there was not any water flaw anymore) pressure on the house side slowly
started to drift up. This looked like pressure regulator did not close
completely and pressure started to rise. Ok, I expected the outlet pressure
will simply equalize with inlet. This did not happened and somehow outlet
pressure became 10psi grater then inlet pressure before it stopped to drift up.

How come this is even possible?

Any ideas are very welcome.

Thank you,

- Vitaliy

PS.
Pressure regulator installed horizontally (another words, the control bolt is in
a horizontal position).
Does it really matter?
I did not find any restrictions how regulator should/must be installed.

 

[Gary Slusser]

If you don't have an expansion tank for your water heater, you may need one now that you installed the PR valve.

Gary
Quality Water Associates

 

[Sponsor]

 

[Dunbar Plumbing]

In further detail, an expansion tank is required on closed water systems, which is what your PRV created. Water goes through a PRV but cannot reverse, thus the closed system, the drawback of a PRV's protective qualities. Water heaters create thermal expansion in the potable water system and therefore it has no place to go. This in turn equates to pressure. Your temp dial on your water heater dictates how much thermal expansion can become. Get on the search engines and search under thermal expansion/water heaters and I'm sure that it would turn up something. The expansion tank normally can go anywhere on the cold side potable water system, but it is best to install the tank closest to the point of origin of thermal expansion, the water heater.

 

[Vitaliy]

Hi Everybody,
Thank you very much for your answer and advice.
I almost came to the same conclusion myself.
More observation - and I have noticed this phenomena happened when
heater was on but water was not used.
I think, hot water expansion tank now is a must.

Now I have few more questions:

- What kind of expansion tank would you recommend (brand, size, etc.)?
I have 40gallons “Superstore†indirect water heater, equipped with “Watts
100XL (150psi, 210F) pressure/temperature relief valve. I searched the
forum but did not come to any conclusion on brand/size of expansion tank.

- Should I worry about periodic over 100psi pressure in a system and do
something before I will install this expansion tank (uninstall PR, open PR to
the max (looks like my PR does not have built-in bypass mode)?

- Is this a requirement by any code to have an expansion tank if PR is used?
(I am sorry, I am not a plumber at all.)

Thank you,

- Vitaliy

 

[Dunbar Plumbing]

Depends on the area you live in dictates whether or not it is code or not. But whether it is a requirement or not is irrevalent, the issue is still the same. Since you only have a 40 gallon water heater a 2.5 gallon tank is all you need. Those are the cheapest tanks to buy and will serve the purpose you need. Can be found at all stores and plumbing supply houses in your area. The good thing is that you are willing to take care of the problem which is really good.

If you buy a Watts Thermal Expansion Tank it specifically states that you must pressurize the expansion tank to the working pressure of your home. That way the bladder is not expanded in either direction but flat when thermal expansion occurs. This prevents premature wear. Go to www.wattsreg.com and the PDF files on thermal expansion tanks dictate this info.

 

[Master Plumber Mark]

get the big one

the bigger the better for an expansion tank....

we used the smaller one and they just dont have the muscle
for the job...they wear out quicker too.....

the bigger one is the better way to go
its about the size of a medicine ball


the price is about 45 bucks+-

http://www.wattsreg.com/default.htm?/thermalexpansion/




they are pre-primed to about 50psi,
just pump it up to about 60 lbs and it will work fine


you might notice a small pressure rush
when you open the faucets that goes away in about
3 seconds. thats about normal when you install one.

 

[Vitaliy]

Hi Guys,

Thank you all for explanations and suggestions.
Most likely this will be over killer but my preference to have a lot margins in
a system (I am an electronic design engineer with a lot of experience) so,
I ordered 8.5gallons Watts DET-20 M1 expansion tank.

One more question:
If I would like to maintain 50psi water pressure in the house why I would
need to pre-charge tank to 60psi (by specification pre-charge pressure
is 40psi)? 50psi (actually the same as set by PR) sounds like more reasonable.
Please comment why 60psi would/should be better then 50psi?

Thank you,

- Vitaliy