Two pipe Air Vent System - Main vent questions...

drtom

Okay, I am confused. My understanding of main vents is so you can get the air out of the supply pipes to allow the steam to get to the radiators as fast as possible.

In my house, I have a two pipe system (old style without traps). The main vents are on the return pipes. I have been thinking about getting faster vents for the mains, but in my system, the radiators fall between the boiler and the main vents. Do I still want to vent this system as fast as possible? Will using faster main vents on the returns get the steam to the radiators faster? Have I explained myself comprehensibly?

On a typical two pipe system with traps, are the vents on the returns or on the supply lines?

TomM

venting

in my case I vented the tops of the risers, vented each radiator, and vented the end of the dry return before it became a wet return.  I calculated the volume of air in each, and vented appropriately. 

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my house is a 2 pipe air vent system, with three floors, and 3 sets of risers/returns.  Each riser/return set has 3 radiators connected to each, one on each floor.  They are 'wired' in parallel. 

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the problem with venting just the radiators and the dry return is such that steam would flow through the radiators on the first floor, and then flow into the dry returns, and THEN heat up the radiators on the second and third floor.  I don't really care about heating the dry returns.  Once I vented the risers, it balanced out pretty well and the radiators heat up pretty much at the same time. 

Steamhead

On a 2-pipe air-vent system

we must NOT vent the return lines from the radiators. This will allow steam to get into them, which we don't want. If there is a dry return from a steam main with a vent on it, that's OK.



However, not all 2-pipe systems without traps are air-vent systems. A 2-pipe air-vent rad will almost always have a shutoff valve on the return as well as the supply connection, AND an air vent. If this is not the case, it might be a Tudor, Kriebel, Thermal, Moline or similar system.



Post some pics if you're not certain.

TomM

comin off

well i guess that vent's comin off  :-)

drtom

no main venting on a two pipe system?

Am I understanding you correctly? You are suggesting that I do not vent the returns on my system? This means that ALL venting must happen at the radiators? When the steam enters the radiator, some air gets vented at the radiator, but I am sure that much of the air gets pushed out the other pipe on the return side of the radiator. Are you sure that I shouldn't vent those lines before the air gets back to the boiler?

Steamhead

That's correct

The returns on a 2-pipe air-vent system are not intended to vent air. There's nothing to keep steam from jumping from one radiator to another thru the returns once it gets in there, so we want to keep the air in the returns. If we keep the pressure low (with a Vaporstat) and vent the steam mains quickly, not much steam will enter the returns.



If your system is not a true 2-pipe air-vent system, all bets are off. Post some pics if there's anything you're not sure about.

drtom

Yes, true two pipe air vent system...

Why would the dead men have vented the returns on this system? And why does it work?

Also, I am not sure where "main vents" would go on this system, but apparently I do not have any main venting.

I have a number of pictures of my system on THIS thread...



http://www.heatinghelp.com/forum-thread/133282/Need-help-understanding-my-system-Loonnggg-post#p1208988