Double radiator vents

AlexR

LAOSH mentions that you can put two vents on a radiator for quicker venting of a long runout or riser. The second vent goes below the first so that it closes sooner and prevents too much condensate from draining too fast when steam hits the radiator.



My radiators have a flat disk, about 1/2" diameter on both ends. The one on the non-valve end is drilled and tapped for the vent. This got me wondering- if you're adding a second vent, why not put it on the end closest to the valve (one pipe system) rather than low on the far end?



What're your feelings about the second vent? We're on the second floor and some of the radiators have a 20' unvented, insulated runout.

jpf321

it's probably ok

To put the vent on the supply side...afterall you are using it to assist with venting the supply pipe...as soon as ANY vent on the radiator closes de facto the supply pipe is fully vented :-)

nicholas bonham-carter

multiple vents?

before going to that trouble installing a second radiator vent, double-check your main vents.

the mains should fill quickly, and then the risers have air in them which will be let out by the radiator vents.

if this riser is close to the end of the main supply, then its slowness may be due to slow main vents.--nbc

AlexR

this time with a picture

jpf321: right, I figure it will work.  I was curious why it's not the default since it seems like it'll close the vent faster.



n-b-c: The mains are vented with a gorton #2 each and seemed to heat quickly, but I'll confirm that and maybe check the vents.  Unfortunately, the mains aren't that long compared to the runouts.  In the picture, the thick black lines are the vented mains and the thin black lines are the counterflow runouts.  Radiators K and B (and to some extent L) are the ones that seem slow. 



I guess I was asking when you'd consider a second vent on a radiator, eg, if the runout+riser is more than X feet.  I suppose the right answer is when the pipe volume divided by the venting rate is too long.



thanks for the replies!

AlexR

answering my own question

Using the charts from "Balancing a Steam System using a Venting Capacity Chart", it shouldn't take more than a minute to vent the mains and 3 or so to vent the runout + riser.  So I don't think it's a venting issue.  I guess the next step is to check the rest of the vents for clogging, make sure the LWCO isn't tripping for some reason, and then blame it on uninsulated risers in the walls.