Air Separator

Joe Mattiello_2

See attached for a diagram of two separators with plain steel type tank.

mark_28

Air Separator

Quick question: When using a centrifugal air separator with a conventional horizontal expansion tank, is it necessary to pipe uphill from the top of the separator to the tank fitting for optimal air escapement? I have always laid out the tank quite a bit higher than the separator but I'm doing a job now where that's not so easy. Comments?

Mark

Brad White_17

I believe you do

have to pitch upwards continuously, Mark. Not that it is the best reason why, and is sometimes the worst reason why, but "I have always seen it done that way"....the principle being a way to charge the tank using bled air.

If you do not and have a dip in the expansion line, you will have a slug of water sitting there moving with every change in system pressure. Thinking a splashing noise issue at least. Not sure what that water seal does to the tank's effectiveness. Never seen it done.

Is there an alternate location you can connect the tank to the system? It need not connect to the air separator, all that needs is an auto vent piped to drain. Your PONPC can be further along at a more convenient location upstream of the pump.

Question: Why not use a diaphragm or bladder tank? Or a Spirovent for that matter? I assume it is a matter of cost or of facilities standards. Not a challenge, just curious.

Boilerpro_3

You can pipe it below the air seperator

but will need to pump from the top of the air sepatordown below the tank and then install another air seperator here and connect its top to the tank. Looks strange in the B G books, but it makes sense.

Boilerpro

mark_28

air separator

Both the tank and the separator are existing components in a sytem that is undergoing a severe rearraingement. I am too short on $$ to consider changing tanks, as much as I prefer the diaphragm type. The air vent and and alternate tank connection might work - I'll look at those B&G books when I get back to the office tomorrow. You know how it is - this was the last thing I looked at before knocking off for the evening and I just couldn't let it alone knowing all you guys are out there.

Mark

Brad White_17

That does sound

odd, BP, but it makes some sense from the tank connection standpoint. Good way to sell air separators anyway! Why even have the first air separator when a vent alone might do? Just to vent the gross air and leave the more disolved air for the second pass? Curious.

Brad White_17

Hey Mark-

Please send a picture of this beast when you are done, would you? Has me curious now...

Best,
Brad

mark_28

Dan Holohan has his usual excellent description of how the tank and airtrol work together in "Pumping Away". I'm going to lower that separator.

Mark

Joe Mattiello_2

Air control/ air elimination

When using a conventional type expansion tank you shouldn’t use any air vents, because as the air is released through the vents, the air cushion in the tank can be depleted leaving the tank water logged and the system pressure control gone. Now with a water logged tank the thermally expanded water is going to seek a new outlet like that pressure relief valve. Air elimination using a diaphragm type tank is a great alternative to a plain steel tank for many reasons including the problem your currently facing.

Joe Mattiello
Technical Support Technician
Tel. 401-942-8000 X 484
Fax. 401-942-2360
joemat@taco-hvac.com

Brad White_9

One point of information, Joe

I can see that if baseboard or properly piped HW to cast iron.

But if you have older standing cast iron radiation (piped across the bottom, rightly or wrongly, but we do), I would maintain that you will need vents for these if you want full capacity. Otherwise your radiators, especially at the second floor, act as expansion tanks and underperforming radiators in the bargain!

But then, this is academic. Replacement of the old style tank with a diaphragm tank makes it all moot.

Did I miss your point about which vents should not be installed?