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NORA Oilheat Technicians Manual

Steam travels through a system because of a subtle difference in pressure. Besides friction, the fire in the boiler and the condensing of the steam in the radiators also leads to a difference in pressure throughout the system. The fire creates the initial pressure. Since all the air vents are open, the inside of the piping system is at atmospheric pressure and steam begins to move from the higher pressure in the boiler to the lower pressure in the system. As soon as steam begins to move, it also begins to condense into water. When steam condenses into water it leaves a partial vacuum in its place. Since steam occupies about 1,700 times the volume of water, when it condenses it shrinks to 1/1700th of the space it occupied as steam. What we’re left with is a partial vacuum that makes the steam travel to the radiators. This is why you don’t need pumps to move steam. The boiler’s job is simply to get steam (a gas) out to the last radiator before it turns into water (a liquid.) The importance of the piping around the boiler Today’s replacement steam boilers contain much less water than the boilers of yesteryear. As boilers became smaller, the piping around them became more and more important. If you want your replacement boiler to work, you have to pay careful attention to the boiler manufacturer’s piping instructions. Here are a few of the things the boiler manufacturers will tell you to do: • Allow at least 24 inches between the center of the gauge glass and the bottom of the steam header • Use full-size risers to the header • Pipe the system take-offs at a point between the last riser to the header and the equalizer • Pipe swing joints into the header • Use a reducing elbow to connect the header to the equalizer The dimension labeled “A” in Figure 13-20 represents the distance you have to maintain between the center of the gauge glass and the bottom of the lowest dry return in the system. Dimension “A” In one-pipe systems “Dimension A” must not be less than 28 inches. “Dimension A” provides the force that puts the condensate back in the boiler. Without it, water will back up into the horizontal piping and block the take-offs to the radiators. The house will heat very slowly Chapter 13 Heating Systems Figure 13-20: One-Pipe steam system 13-16 Heating Systems Radiator Supply Valve Air Vent Main Vent Radiator Riser Dry Return Wet Return Hartford Loop Equalizer 28" Minimum “A” Dimension Take-Off Riser Relief Valve Pressuretrol Low Water Cutoff


NORA Oilheat Technicians Manual
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