Radiator Vents

Gaskets

What back pressure do you want to keep on the radiator...and how many minutes do you want it to take to vent all the air out.

nicholas bonham-carter

venting back-pressure

as the radiator vents are so small, and only handle the air in the riser and the radiator, you won't see much back-pressure. the main vents do all the air removal, and there you will see on a good low-pressure gauge, that the air is leaving at 2 ounces [sometimes less].

the time for the mains to fill with steam varies with the length and diameter of the pipes. all you know by looking at the gauge is that there is no restriction on the escaping air.--nbc

Gaskets

Radiator Vents

Is it possible then to vent the radiator too fast?

Steamhead

Of course!

in a one-pipe system, the water must flow back down the same pipe the steam comes up. If the steam rushes up the pipe and into the radiator too quickly, the water won't be able to drain back, and this can result in banging. So we vent the steam mains quickly and the radiators more slowly.



For example, we want a steam main to fill with steam in a minute or two (measured from the time the boiler starts producing steam) but a radiator can take 10-15 minutes or so. I also like to size my main vents for one ounce of pressure, my riser vents (if used) at 2 ounces and my radiator vents at 3 ounces. This helps make sure the steam fills the mains first, risers second and radiators last, leading to good system balance.



Gerry Gill and Steve Pajek's venting e-book shows venting rates at different pressures. If you don't have a copy, get it here:



http://www.heatinghelp.com/products/Steam-Heating-Books/25/146/Balancing-Steam-Systems-Using-a-Vent-Capacity-Chart-by-Gerry-Gill-and-Steve-Pajek