Boiler Facts New Steam Boilers Old Vapor-Vacuum Systems What could possibly go wrong? By George R. Carey, Jr. Vice President, Fluid Industrial Associates, Inc. gcarey@fiainc.com twitter: @Ask_GCarey the boiler was by “stacking” up in the return line. Unfortunately, the condensate needs 30" of vertical height for every pound of pressure in the boiler. By the way, this height is measured starting at the boiler’s water line. Most basements didn’t have this clearance, and so the boiler return trap was conceived. When the old boiler was in operation, due to its physical size, it contained a large amount of water. This was very beneficial to the system’s operation. When the thermostat called for heat, the burner turned on and the boiler started to make steam. This steam leaving the boiler and going out into the system caused the water level to go down. Once out in the system, the steam would eventually condense, giving up its latent heat and turning back to condensate (water). The condensate would then drain back to the boiler room where it would try to reenter the boiler. If the pressure was too high, the condensate would start to stack in the returns until it backed up into the condensator. The float inside the condensator would rise up, opening a valve and allowing a shot of steam into the condensator. The condensate would then slide back into the boiler and started the cycle all over again. The boiler never flooded, though, because it held so much water that the level never dropped into the automatic feeder’s range. You could say that a balance existed between the boiler’s water content and the system’s time lag. However, a new, properly-sized boiler contains less water—a lot less. This makes all the difference in the system’s operation. Now, as the water leaves the boiler as steam, it still takes the same amount of time to come back to the boiler room as with the old boiler. A new, properly-sized boiler contains less water—a lot less. This makes all the difference in the system’s operation. I am not sure why, but this heating season I have been called out to help solve the same problem with several different steam systems. Each time, a new steam boiler was installed into an old vaporvacuum system and now the new boiler constantly floods or cycles on and off on its low water cut-off, waiting for condensate to return to the boiler. The houses in all of these jobs are the same: high-end circa-1920’s mansions, which makes sense. At the time, only rich people could afford these “Cadillac” heating systems. They were the best central heating system money could buy. Years ago, when these systems were being installed, people thought the heating systems were contaminating the inside air. To combat this issue, the heating engineers of the day decided to both ventilate and heat the house with a constant supply of fresh air. This, of course, increased the cost of operating the system, so it was found only in the homes of the wealthy. With all vapor-vacuum systems, they would use an old cast-iron vent trap located at the end of the dry return. This vent would have been the only one used for the entire system, which is characteristic of vapor-vacuum setups. The other device located near (and usually a few inches below) the vent was a condensator—sometimes referred to as a boiler return trap. The return trap’s job was to help the condensate draining back from the system to get back into the boiler while it was under pressure. This device was needed because of the effect steam traps had on the condensate that was returning from the radiators. In addition to allowing air to vent and condensate to drain from the radiator, the trap also prevented steam from passing into the returns. This was a good thing for maintaining steam distribution throughout the system, but bad for the condensate trying to return to the boiler! Now, the only force the condensate had to return back into 22 ICM/March/April 2015
ICM September-October 2014
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