Preferred location for air separator and expansion/compression tank in primary / secondary systems

delcrossv

I've seen it pictured both ways- tank and air sep on the primary loop; tank and air sep on the secondary loop before the secondary circulators.

Question is, which works better - and why?

Also, any difference if it's air management (Airtrol) or air elimination (everyone else)?

hot_rod

wherever you install the expansion tank in the piping, that becomes the primary loop

It could be the boiler loop, or it could be the distribution loop

You need to look at both circuits, picture in your mind, or analyze the pressure drop of both circuits to assure all circuits stay above fill pressure when any or all circulators are running

With an air management system the Airtrol fitting goes into the boiler and pipes to the expansion vessel, so that would dictate boiler is or is in the primary loop

The Steam Whisperer

Yes, I've often contemplated that too. If its on the boiler loop, especially with a high temperature boiler, its nice having the higher temperatures to help drive out the air. On the other hand, having it in the system loop gives the air separator a crack at all the water running through the system. Probably a conventional air scoop (taco, amtrol etc.) would be best in the boiler loop, with microbubblers in the system loop. The B&G IAS may be able to go either way.

delcrossv

You can put in more than one IAS / scoop and gang them? Seems there'd need to be a check valve in there.

FWIW, B&G hasn't made an Airtrol boiler fitting in a while. Now they say to attach a line from the top of an IAS to the Airtrol.

hot_rod

no issue having multiple air seps. But only one expansion tank connection. Same issue or question comes up with indirect tanks that are parallel piped

On the system side maybe a combination unit is a good option. Air, dirt, and magnetic separation, especially on old iron systems

delcrossv

https://forum.heatinghelp.com/discussion/comment/1810881#Comment_1810881

So, would this work? Connect boiler air scoop to compression tank Airtrol (primary loop) and put an air vent on microbubbler on the Secondary loop?

Or tie outlets of both air seps to a common line to the airtrol? That seems funky as you'd have two Points of No Pressure Change.

hot_rod

the actual connection point of the one expansion tank is the PONPC. That exact tee branch into the system piping.

The tank does not need to be physically at that connection, you can pipe to another location. Obviously a compression tank is not mounted on the boiler Airtrol fitting, but piped to a tank above.

Adding additional air elimination devices doesn’t change that PONOPC

If you add additional expansion tanks, at different connection points, then the PONPC is a moving target

“Pumping Away” is a good book to own if you want more info and pics on expansion tank how and why.

delcrossv

@hot_rod Thinking of something like this:

Within the dashed box.

EdTheHeaterMan

@delcrossv. This is where you need to see the water and air pressure in your minds eye.

Here is an example of what two expansion tanks might look like on a closed loop system. See what happens when the system is charged to 15 PSI and both tanks have 15 PSI water pressure. There is equal parts of water in each tank if for example both tanks are charged with 8 PSI when not connected. 8 PSI pre-charge plus that additional 7 PSI of the water static pressure will increase the tank air pressure to 15 PSI when there is 15 psi on the water side.

If you have a pump that has a differential pressure of 10 PSI when operating, then one side of the pump must increase in pressure while the other side must decrease in pressure. in the lower diagram you can see that the tank on the inlet side must have a lower pressure. This lower system pressure will reduce the water pressure in the expansion tank. When the pressure drops on that side the air pressure of the tank will push the water out of the tank. When that water leaves the tank on the inlet side it needs to go somewhere, and since the pressure is higher on the discharge side, that water can compress the air in that other tank, the water that left the inlet side tank will find itself in the Tank on the discharge side.

1. All of the components of the system are not represented above.
2. There is no additional water was added for this test.
3. Just the components that are needed for the topic are represented
4. The temperature of the water stayed the same
5. Only the names have been changed to protect the innocent.

delcrossv

@EdTheHeaterMan makes sense, but I only have one tank in my drawing, but connections at two points. Seems I could get back flow through the connected pipe.

Ok, solves that question. :)

The Steam Whisperer

If using a conventional tank, you can only have one air separator. If you install a second one, The air from the tank will gradually be reabsorbed into the water and the second separator will vent it to the atmosphere. You will eventually lose the air charge in the tank, and start popping the pressure relief valve. WE've seen this problem numerous times, along with its cousin….people keep bleeding air from radiators ( which make great air separators) and the conventional tank loses it air cushion. Air tends to end up in the radiators because the air separator is missing or poorly located.

EdTheHeaterMan

Then you may have this. and that will just make you circulate a little less water thru the system and move water thru the tank connection piping. I'm not saying that you have your connection pipes set up that way but if you did, then you have created another path for water to circulate, like another zone.

Again this is where you draw a diagram and use your minds eye to see the water and air move and chang pressure.

And one other point to consider… if you are not using a bladder or diaphragm tank where the air and water do not come in contact, Then you cannot use automatic vents. To be clear. Auto air vents = Extrol tank

If you have the steel compression tank where the water is in direct contact with the air at the top of the tank, Then you must close, cap off, or remove any automatic air vent. You don't want any air leaving the closed system. You want to direct any air in the system into the steel compression tank.

delcrossv

Thanks @The Steam Whisperer and @EdTheHeaterMan . One tank, one air separator on the boiler loop. All good.

hot_rod

I would use a good air sep at the boiler, the vent pipes up to the tank fitting

The Caleffi Discal has an npt adapter fitting for remote venting the discharge air