Expansion tank and regulator back flow pressure issue

**IAMIR** · 07-01-2010, 07:50 PM

This past winter I replaced my HWH and Expansion tank (both were bad). However when the HWH heated up to the Medium set point the relief valve started spitting water. Basically it was doing its job. I went over to the Regulator back flow valve and turned it down a lot. That seemed to stop the HWH from spitting. But now that summer is here the water pressure doesn't even work the lawn sprinklers properly. I have roughly 42 psi at the hose bib. It was around the same when I tested the HWH with the hot water running out of a different sink. The new Expansion tank was factory set at 40 psi with a max of 150. My HWH is a 50gallon capacity and the regulator back flow valve can range from 25-75 depending on set point.

My question is this. If I were to boost the regulator up to 60 psi would I also need to set the Expansion tank at 60 psi? Do they need to be equal or does one need to be greater than the other?

Signed,
An electrician....now you know why I am asking

**Redwood** · 07-02-2010, 05:20 AM

Short version: With the expansion tanks match the pre-charge to the system working pressure not to exceed 80-psi...

Long version: http://media.wattswater.com/2915054.pdf

**IAMIR** · 07-02-2010, 05:57 AM

*sigh* I was all over the Watts website looking for something like your link and couldn't find it yesterday. Thanks for responding.
Have an awesome 4th of July and don't forget to say thanks to a veteran.
Peace,
Chuck

**Redwood** · 07-02-2010, 05:24 PM

Thanks Chuck! Happy 4th To You As Well

Glad to help you out...

**IAMIR** · 07-02-2010, 06:32 PM

BTW...I did check the pressure which was at 40. I bumped that up to 60 at the regulator, drained the lines, and set the exp tank to 60. All is working great. I can actually use the sprinklers now.
Thank you for serving this great country!
May God bless you and all our troops.
Again, Happy 4th
Chuck

hj · 07-02-2010, 06:42 PM

As a practical matter, the air pressure in the tank if rather UNCRITICAL, because it will stabilize at the house pressure as soon as you turn the water on.

**Redwood** · 07-02-2010, 09:12 PM

Originally Posted by hj

As a practical matter, the air pressure in the tank if rather UNCRITICAL, because it will stabilize at the house pressure as soon as you turn the water on.

Unless of course the precharge is so low that the tank is so full at the house pressure there isn't enough capacity left to cover the amount of thermal expansion. (Bladder wear may be excessive)

or,

The precharge is set to high and again it can't absorb enough of the pressure from expansion.

**zl700** · 07-02-2010, 09:17 PM

Actually to get full use of the capacity of the tank, the air charge is supposed to be set 2 PSI below normal static water pressure, with no water pressure pushing against it. But the same is good enough.

hj · 07-03-2010, 08:11 AM

The two times the air charge is critical is if it is ZERO, meaning there is no air volume to absorb expansion, or higher than the tank's T&P valve's setting, i.e., 150 psi, so there is no way the water pressure could overcome it to enter the tank.

**Redwood** · 07-03-2010, 01:21 PM

Originally Posted by zl700

Actually to get full use of the capacity of the tank, the air charge is supposed to be set 2 PSI below normal static water pressure, with no water pressure pushing against it. But the same is good enough.

That would be the recommendation for well tanks...
For expansion tanks this is not the case and as HJ stated pressure is not critical unless it is way way off...

**zl700** · 07-04-2010, 01:28 PM

I love how hard headed you guys get.

Per Watts:
The expansion tank pre-charge must be set to the system pressure as
determined in Step 1. Pre-charge prior to installation in the system.
Caution: Pre-charge prior to installation in the system.
Do not adjust the air pre-charge of the expansion tank
with the system under pressure. The air pre-charge
should only be adjusted under zero system pressure.

My recommendation for 2 PSI below works best as to use full capacity of tank as I stated earlier

Difficult to argue, following instructions, and not making up your own theories makes for an easier and proper install with less callbacks.

Let me remind you, master plumber title does not make you manufacturer product experts.

**Redwood** · 07-04-2010, 01:42 PM

Per Watts:
The expansion tank pre-charge must be set to the system pressure

What is hard headed about following the manufacturers directions?

I suspect watts does know their own products...

Amtrol another manufacturer of thermal expansion tanks also states...

2. Adjust pre-charge to equal system fill pressure.

Extrol Instructions PDF

Pre-Installation
1. Visually inspect EXTROL
® for any damage.
2. Adjust pre-charge to equal system fill pressure.

3. Replace and tighten plastic cap on air fitting.