Setting Correct Pressure

TheTaxButler

Hello all, this topic may have been covered but I was unable to find this exact question on the forum. We have a hydronic heating system on our split level. I am needing to purge the system and add back to remove air & set correct pressure on my three zones.

When adding water do I keep the valve open for the pressure relief tank? Picture of tank is attached.

Jamie Hall

The technical term -- always helpful! -- for that tank is a compression tank. Handled correctly, they last forever and never give trouble. Nice to have!

That said... they do need to be piped and handled correctly.

The simple answer to your question is yes, keep the valve on the line from the system to the tank open when adding water. That way the air pressure in the tank will always be nicely the same as the water pressure in the system, which is the objective of the exercise.

Now. If you do drain the system down for some reason -- again, keep that valve open. This will allow air into the tank, which you need to have in there as a cushion.

There must be NO other air bubble removers on the system other than the fitting which connects the pipe to the tank to the rest of the system. It is not unusual for people to add air removal gadgets of one sort of another during later work, since they are required for systems which use bladder tanks. If there is one on a compression tank system, it will lead to the compression tank losing that air cushion (becoming "waterlogged") which will keep it from working properly. This is not hard to fix -- though it is a nuisance. If it should happen, close the valve to the rest of the system and open the tank drain valve and let all the water out. Then close the drain and open the valve back into the system. You will need to add a little water to the system.

TheTaxButler

Jamie, that is good to know & I thank you for the breakdown. There is an air bleeder on the system connected to the boiler & right before the emergency pressure relief. I've included another picture. This was already present when we purchased from the home.

Since you mentioned it, we had a huge issue the 1st or 2nd year we were here. Compression tank became water logged & couldn't take the expansion from the system which led to huge pressure buildup, lots of banging & eventually emergency pressure relief was triggered! Maybe that little air bleeder is the culprit but I could swear I have seen somewhere they were required by building code? I have since drained the compression tank but am thinking I may need to again as part of this process.

Jamie Hall

That little air breather is doing you no favours at all. The safety valve on that pipe is required, yes -- but the breather, no.

hot_rod

The air vent on top of the boiler is handy for the first fill to get all the air out of the boiler. With a compression tank, you would want to screw down the black plastic cap after you vent. It could be causing the tank to loose it's air bubble.

Any other air purgers in the system? if so they need to be piped to the tank.

You have an "air management" type of system. So you need to make sure the air stays in that tank.

Ideally, with a tank like that you would have a special fitting in the boiler and in the tank to manage air.

B&G Airtrol is one brand.