Air Locking a Two Pipe Steam System
When the conversion from constant firing coal boilers to intermittant firing gas and oil boilers took place, an interesting problem developed. The problem was on certain structures the radiators in the far flung areas of the house or building weren't heating the rooms. The cause of this was steam heating the closer radiators to the boiler before steam was even present at the far end of the building.
See if you were the steam, and all you were looking for was that vent opening, and your cruising down through the steam main, you come across the first radiator and you suddenly see the main vents on the return pipes just as well as you see the main vents at the end of the steam main. And they may even appear closer than the vents at the end of the steam main. You see those return vents because the traps on the radiators are open until they are hot, which they are not. So since your the steam, you go across the first radiator to try to get at those return vents. This is not the ideal way for a steam system to operate. Its going to show itself as poor steam distribution. The closer radiators to the boiler will heat first and the far flung radiators will heat last. Problem is the thermostat may get happy and shut off the boiler before the far flung radiators have actually heated the room. So those rooms will be cooler.
In 1931 a fellow named Fred Raymond came up with the method of air locking steam systems to force the steam to go to certain areas by controlling how the air was removed from those areas. He utilized special vents that had differing weights on the moving internals. The steam being lazy would go for the easiest air vents to open first. It was a beautiful design and brillant in concept. Of course those vents are no longer made. So we came up with a system that mimics his design principals using electrically operated steam rated zone valves to control the movement of the air.
Its actually a very easy system to employ and the comfort increase is well worth the expenditure.
We have done this now in many large homes and a couple of two pipe steam equipped apartment buildings. The results have always been very good.