Understanding Steam Systems

f you are installing a low pressure steam boiler for a micro brewery, throw out everything you know about hydronic boilers. The operation of a steam system is closer to the operation of an air conditioning unit than it is to a hydronic boiler. The water inside a boiler will change state from a liquid to a vapor and then back to a liquid during the heating process. 

I once had a vehicle which was incredibly difficult to pump gas into the tank. The gas pump nozzle would shut off and no matter how I placed it, filling the gas tank was a frustrating time consuming task. The reason was the air could not escape the tank through the narrow nozzle and would shut off the gas pump. It reminded me of a steam heating system. For steam to enter a void, the air has to be removed. The first rule to remember with steam is two gases cannot occupy the same space. The system will either have steam or air. When the boiler is off and the piping is cool, the system is filled with air. On a call for heat, the burner starts and heats the water inside the boiler. Once the water gets warm enough, it will change state and become a vapor, steam. This change of state is called Latent Heat and the water will expand at 1,600 times its volume when changing to steam. The steam leaves the boiler at a speed of about 30 miles per hour looking for someplace cold where it can surrender the latent heat and revert back to a liquid, condensate. The steam pushes the air ahead of it and the air inside the piping is vented through the vents on the piping or through the steam traps into the return piping and out the vent on the condensate tank. Once the system is satisfied, the burner shuts off and the steam condenses. When the steam condenses and reverts back to water, it will shrink back to 1/1600 of its size. The void caused by the steam condensing in the space will be filled with air sucked in from the air vents or condensate tank. A simple way to troubleshoot a steam system is to try to imagine the system breathes. The boiler exhales steam, pushing air from the vents. The system inhales air when the boiler shuts off. If a steam heated component is not heating, it usually means air is trapped somewhere in the system. 

Can Air Escape?When working on steam systems, the piping will either have steam, condensate or air. For steam to enter a pipe or vessel, the air has to be removed. When trouble shooting steam systems, ask yourself this simple question, If I were air, how would I escape the pipe or vessel? If the system uses traps, the air will leave with the condensate via the traps. Look on the outlet piping of the trap for sagging pipes as this will create a water seal and stop the air.