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NORA Oilheat Technicians Manual

Chapter 5 Nozzles and Chambers Figure 5-19: Combustion chamber design Good Combustion Preferred Shape Eddy Current Pockets Eddy Current Pockets 5-18 Nozzles and Combustion Chambers chamber first. If the old chamber is deteriorated, wrap the material with a stainless steel binder. If the old chamber was too small or the wrong shape, lining it will not help. Ceramic chambers become brittle after firing. Do not touch it with a vacuum cleaner hose or flame mirror after it has been used. The material is intended for firing rates below 3 GPH, and will withstand about 2,300°F. It can be purchased by the foot or is available in pre-shaped sizes. The material gives quieter operation, less smoke and fuel savings. Molded chamber: Many manufacturers install their own molded chambers in their packaged units. They are usually made of semi-insulating refractory material. Chamber shapes The best shape for a chamber is round or oval so the hot gases can sweep back smoothly. In a square or rectangular chamber, eddy currents develop in the corners requiring more excess air to burn completely. The correct height is most important. All combustion should take place in the chamber. There should be little if any flame above the chamber. The top of the chamber should be about as far above the nozzle as the floor is below it. See Figure 5-19. Sizing the chamber The gallons-per-hour firing rate determines the size of the chamber. A firing rate of .75 to 3 GPH requires 80 square inches of chamber floor space per gallon of fuel. A firing rate from 3.5 to 5 GPH requires 90 square inches, and over 5.5 GPH requires 100 square inches per gallon. See Table 5-2 and Figure 5-20. Installing a low firing rate chamber There are many very good pre-cast absorbs much more heat before it begins reflecting any back into the burning zone. It is unsatisfactory for residential purposes, but is used in commercial units because it stands up better to the shock loads of high firing rates. The brick comes in the standard size of 9" long by 4.5" high, and 2.5" deep. It is also made in runners and pre-cast chambers. Metal fire chambers: Metal chambers are used primarily in factory-built “packaged units” because they can be shipped in place without damage or breakage and do not require bracing. Metal chambers are much better than common fire brick. However, they are sensitive to improper nozzle selection and overfiring. A nozzlefiring rate that is too high, or a lopsided fire can distort or even burn a hole through the wall of the chamber. Direct flame impingement on the chamber must be avoided. Metal chambers must have free flowing air behind them to keep them from burning through. Do not put any kind of insulating material, including soot, around the chamber. The higher flame temperatures of flame retention burners is tough on metal chambers; it is usually a good idea to replace a burned out metal chamber with a pre-cast ceramic one. Ceramic chambers: Ceramic material is excellent for chambers. It reflects heat quickly while absorbing very little and it is easy to install. If the old chamber is still in good condition, you may use ceramic blanket material to line the old chamber. Be sure to seal any air leaks in the old


NORA Oilheat Technicians Manual
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