System pressure reduction

Mark_46

Brad,

Great.

I confirmed a few things in the the 1156f install sheet from Watts' site.

You were correct, "To raise the reduced pressure - slowly turn the adjusting screw clockwise until the system gauge indicates the pressure required. To lower the reduced pressure - turn the adjusting screw counterclockwise".


Also, they provide a little formula to find the required pressure.

A. Calculate the number of feet from the regulator to the top of highest radiation.
B. Multiply this number by 0.43 and add 3 lbs. This will give the pressure required to raise the water to the highest radiator and keep the system under pressure.

I have about a 23 foot rise from the valve to the highest radiation. So that works out to 12.89 psi. So I will plan to set the system pressure to lets say 13 psi.

But if I understand correctly what youre describing, if the system is cold (under 80 degrees or so?) set the air pressure in the expansion tank to 13 psi? (same as system pressure) If it is hot (over 100 or so?) I would set the air pressure in the expansion tank to about 17 psi, (4 psi over system) correct?

Mark_46

Pressures

My system pressure is about 22 - 23 psi as a result of some service work. According to Heat Transfer, an 80M is intended to operate within 12 - 15 psi.

How would I go about reducing system pressure by about 10 psi without introducing air into the system? Or worse, ending up with an air bound system. I presume the pressure reducing valve is the key here? It is a Watts 1156F. Is the system pressure adjustable through this device? If so, how?

Also I presume the expansion tank bladder pressures are adjustable? Mine is an Amtrol Extrol Model 30. I measure 14 psi at the air valve. How is this adjusted and what should the adjustment be based on? Equal to system pressure?

Thanks.

Brad White

Pressure Drop...

Hi Mark-

Dropping the system pressure will not allow air into the system so long as you are pumping away from your expansion tank. The pressure will always be above atmosphere so any leaks go "out".

Just be sure that you drain water off a low point and have any high automatic valves closed off when you do. A sudden draw-down can suck in some sips of air if that. Go slowly and you should not have a problem. Keep an eye on that gauge. Don't spray the cat. They get revenge. Trust me.

Assuming you have a low water cut-off, I would fill the system manually and isolate it. With an auto-fill valve, a small leak becomes a constant replenishment of cold water. If you do use the valve, the 1156F has a set-screw on top and a lock-nut to hold it. IIRC, it is a right-hand to open feature as it depresses the spring, so left-hand turning will lower the pressure.

Hey, if I am wrong, take what I said, hold it up to a mirror ala DaVinci, and do it the way the mirror says...

The Amtrol tank and others like it are fitted with a Shraeder valve (bicycle or tire type valve) which can be bled off or filled as necessary.

Personally and ideally, I specify dry nitrogen as it displaces oxygen, the better to prolong the diaphragm life. Academic point, everyone seems to use a bicycle pump or compressed air anyway and life goes on. A good tire pressure gauge is essential.

If you are Scott Milne, you can use Nitrous Oxide- it works ok and if it does leak out, you really do not care

The tank pressure is set to the same static fill pressure as the system. If you house is two stories, I would say 12 lbs. is plenty.

Mark_46

Hi Brad,

Thanks - I now better understand how these components work.

To confirm - yes, my central heating circulator is located downstream of the air scoop and expansion tank.


Im thinking the procedure would be in this order ?:

1. Close make-up water and zone valves

2. Back all the way off the set screw on the reducing valve.

3. Adjust the expansion tank air pressure to 12 psi.

4. Bleed down at the lowest point to about 10 or 11 psi.

5. Open make-up water vlave. While watching the pressure gauge turn the reducing valve set screw until to 12 psi is reached.

Thoughts?

Brad White

Annotations

Hi Mark- Here are some thoughts to your points:

1. Yes.

2. Check as you do that to see if water enters and stops in which direction you are turning the head. Steady hand there.

3. Yes, but with a cold system. If a hot system is unavoidable, I would go up about 4 lbs. just a guess. That is about the least I would expect a system to increase in pressure between cold and hot. 4-6 lbs. seems about right but why push it?

4. Yes. Slowly. It often does not take much.

5. Yes, then tighten down the lock nut once you are sure your valve setting is accurate. Use a good gauge. Watch the pressure and make note of the temperature. Especially watch the pressure as the boiler fires to limit. If it approaches "lift off" (25 and up toward 30, assuming you started at about 16) you need more tank.

The numbers discussed have all been predicated on a 2-story house so if you have a bungalow or ranch of 1-story, the cold-fill numbers will be lower. I assume you want to limit the pressure to the 12-15 when hot? A lower pressure can be tolerated so long as the system fill pressure can get the water to the top of the system plus 4 or 5 PSI topping pressure. Easy!

Brad White_184

Matching Pressures

Naturally, the best place to start is a cold system, Mark. That way things are stable more or less in terms of temperature and pressure.

Regardless of temperature, the expansion tank bladder or diaphragm pressure will match the system pressure on the other side of it. The two keep each other in check. Imagine if one were higher- something has to give and they want to be equal. Few things in life fight for equality. Pressure is like that.

When I suggested adding a few pounds to account for the fact that the system may be hot, it is just a guess, sort of a form of "Kentucky Windage" whereby backwoods riflemen would aim off to the side to compensate for a cross wind.

Dang, take away my metaphors and I lose all ability to communic