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Posted by HeatPro on April 07, 2007 at 11:04:21:
In Reply to: Steam Radiator vent theory posted by george on April 07, 2007 at 07:40:40:
The steam (air) vent is a simple device that closes when the high temperature of steam warms it. It opens when the temperature drops to let air in.
Steam condensate will fall back down the pipe even when the radiator is getting fed steam (thus requiring valves and pipes that do not trap the water), but as the radiator cools because the burner shut off on thermostat demand because the house is warm enough and the vent opens, there is no more steam entering so water can more freely return to the boiler. Before and after the burner shuts off, the heavy radiator castings emit heat according to their surface temperature.
ALL the radiators would get steam as the burner heats the water to steam, but the speed of venting air through the small holes in the vents regulates the amount of steam to each, so getting the right air venting speed in each radiator is important to even heat.
Generally, as solid fuel burning takes longer to heat the water in the boiler, the vent holes in the steam vents are smaller than in gas or oil fired steam boilers, Otherwise they are the same vents. The original residential steam system designs were based upon having a constant fire over many hours, regulated according to seasonal needs, so venting cycles were much fewer over a season.