air in system


  #1  
Old 02-11-08, 06:25 PM
stingthieves's Avatar
Member
Thread Starter
Join Date: Jan 2008
Location: Wisconsin
Posts: 16
Upvotes: 0
Received 0 Upvotes on 0 Posts
air in system

Is an air scoop or air separator always necessary in a hot water system? Once the water is degassed - what use is it?

Can/May a good system be installed with out it?
 
  #2  
Old 02-11-08, 07:02 PM
X
Member
Join Date: Nov 2005
Location: USA
Posts: 2,338
Upvotes: 0
Received 0 Upvotes on 0 Posts
IMHO, an air elimination device is always necessary (in a diaphragm tank system, which is what I assume you're talking about).

It is useful after degassing if you ever have to drain the boiler for service, the system piping or pumps/valves for service, or any other time water is removed and replaced.

Note that degassing can go on for months, too.

A good system should have a means of air elimination.
 
  #3  
Old 02-11-08, 08:04 PM
F
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 16,321
Received 38 Upvotes on 30 Posts
I've seen systems that ran just fine with a diaphragm-type expansion tank and no air eliminator.

So, is it absolutely necessary to install an air eliminator? No. Is it a fairly cheap "accessory" to help remove the air? Yes.

Would I specify an air eliminator in a system I designed? Yes.
 
  #4  
Old 02-12-08, 05:07 AM
stingthieves's Avatar
Member
Thread Starter
Join Date: Jan 2008
Location: Wisconsin
Posts: 16
Upvotes: 0
Received 0 Upvotes on 0 Posts
thank-you

Thanks for the reply guys - I was wrong in thinking a correctly piped and degassed system didn't need one. May I ask your recommendation where it best to place in a primary loop?

before or after the boiler(s) in the direction of pumping - or before or after the primary loop pump???
 
  #5  
Old 02-12-08, 06:38 AM
Who's Avatar
Who
Who is offline
Member
Join Date: Jan 2006
Location: San Jose
Posts: 2,066
Upvotes: 0
Received 2 Upvotes on 1 Post
It's not necessary.

My old boiler had the pump on the return and a conventional tank up off the supply and always had air problems. As a short term solution (if 3 or so years is short term), I took the conventional tank down, piped a 6" lateral nipple in the tee that was there, added a reducing elbow and then hung an Extrol-type tank from there.

On the return, about 6' upstream of the pump, there was a small riser that lead to an elbow that lead to the auto-fill running above/parallel/horizontal with that return section. I took out that elbow, put in a tee so that there was a smaller vertical riser pipe and then stuck an autovent on the top. I had no scoop, no Spirovent and no air issues. I was actually quite surprised at just how well it worked. I used to get a waterlogged tank at lost once a season before then, and I was always bleeding rads.
 
  #6  
Old 02-12-08, 06:47 AM
X
Member
Join Date: Nov 2005
Location: USA
Posts: 2,338
Upvotes: 0
Received 0 Upvotes on 0 Posts
Most manufacturers would suggest placing the air eliminator on the supply side of the boiler (where the water is hottest and gases most free to be scavenged). Typically, the bottom tapping of an air eliminator is used as the point of connection for the expansion tank and the autofill. Because the system is typically specified for 'pumping away' from the expansion tank, the primary circulator would be downstream from the air eliminator in this scheme.

The important principle here is to pump away from the expansion tank connection, unless the boiler manufacturer specifically calls for some other arrangement.

Traditional style air scoops typically spec 18" of straight piping leading into them. Resorber-style eliminators typically do not have this requirement.

A good diagram of this is at

http://www.spirotherm.com/docs/installation/JrIOM-A.pdf

except ignore the part about the spirotop gizmo. Use it to see the order of components.

There is an emerging school of thought that suggests the expansion tank have a longer distance from the point of connection (i.e., run 4 ft of pipe to it, not 4 inches), to reduce the heat fluctuations on the bladder. Not sure if I have an opinion on this.

It is helpful to install a ball valve between the tank and the system to facilitate changing the tank when someday it fails.

So what's the project? Building a p/s system?
 
  #7  
Old 02-12-08, 12:14 PM
stingthieves's Avatar
Member
Thread Starter
Join Date: Jan 2008
Location: Wisconsin
Posts: 16
Upvotes: 0
Received 0 Upvotes on 0 Posts
Originally Posted by xiphias

So what's the project? Building a p/s system?
I was in an argument re: an air scoop was a must in any wet system - even when installed by the lowest bidder. Air problems in a new consumer installed plant were being blamed on the lack of the accessory and I (stepping on myself) claimed the otherwise as the pump was on the return appeared far too big. Old B/G thing!

Well I have a lead/follow boiler set in series on a primary loop and no air scoop - fact I tossed the scoop when I piped this for myself two years ago - so before I take the opportunity to say something stupid again - I asked for education

Thanks for the help guys!
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: