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American Society of Heating and Ventilating Engineers Guide, 1932 The furnace feeder should be hinged where it is attached to the lower end of the discharge pipe, in order that it may be disconnected from the furnace when the fan is shut down. Also great care must be taken to provide an absolutely tight switch. Otherwise, when discharging refuse to the storage bin, fine sawdust will sift through this valve and settle in the furnace feed pipe, and, in case the fireman has neglected to dis connect the feeder from the furnace, the flame may flash back, following this train of fine sawdust, into the collector. Other forms of collectors or separators are: settling chambers, cloth screen and bag collectors, bag houses, air washers and electric precipitators. For further information on this subject, refer to Chapter 38. DESIGN OF HOODS If the material to be moved is already in motion, as are the chips thrown off from wood-working machines, the hoods should be arranged in the path of the particles so that the velocity of the particles assists the air in carrying the material to the throat of the hood. Hoods should be arranged to draw dust and fumes away from the face of the operator. They should be placed as close as possible to the source of dust or waste material and wherever practical, the hoods should entirely enclose the dust producing operation. Hoods are usually constructed of galvanized sheet iron or other equally substantial and durable material. The material should be heavy enough to withstand the abrasive action of the dust and refuse. The hoods should be of sufficient mechanical strength to keep their shape and should be well braced and substantially supported. Galvanized iron used should never be lighter than No. 22 gage. If acid or corrosive fumes are present heavy material painted with acid resisting paint should be used, or the hoods may be made of noncorrosive material. The exposed edges of all sheet metal hoods should be bound with wire or band iron, not only to give the necessary stiffness, but also to prevent the operator from being cut by the raw edges of the sheets. CONVEYOR PIPES The conveyor pipes leading from the hoods to the fan and thence to the collector are commonly made of galvanized iron, the gage of which varies from No. 24 to 14, depending upon the diameter. The piping should be free from dents, fins and projections on which refuse might catch. All. permanent circular joints should be lap-jointed, riveted and-soldered, and all longitudinal joints either grooved and locked or riveted and soldered. Circular laps should be in the direction of the flow, and piping installed out-of-doors should not have the longitudinal laps at the bottom. Every change in pipe size should be made with an eccentric taper flat on the bottom, the taper to be at least 5 in. long for each inch change in diameter. All pipes passing through roofs should be equipped with collars so arranged as to prevent water leaking into the building. The main trunks and branch pipes should be as short and straight as possible, strongly supported, and with the dead ends capped to permit 356 Chapter 25--Ventilation of Industrial Buildings; Exhaust System's inspection and cleaning. All branch pipes should join the main at an acute angle, the junction being at the side or top and never at the bottom of the main. Branch pipes should not join the main pipes at points such that the material from one branch tends to enter the branch on the opposite side of the main. Cleanout openings having suitable covers should be placed in the main and branch pipes so that every part of the system can be easily reached in case the system clogs. Either a large cleanout door should be placed in the main suction pipe near the fan inlet, or a detachable section of pipe, held in place by lug bands, may be provided. Elbows should be made at least two gages heavier than straight pipe of the same diameter, the better to enable them to withstand the addi tional wear caused by changing the direction of flow. They should pref erably have a throat radius of at least one and one-half times the diameter of the pipe. Every pipe should be kept open and unobstructed throughout its entire length, and no fixed screen should be placed in it, although the use of a trap at the junction of the hood and branch pipe is permissible, provided it is not allowed to fill up completely. The passing of pipes through fire-walls should be avoided wherever possible, and sweep-up connections should be so arranged that foreign material cannot be easily introduced into them. MAINTENANCE OF SYSTEM Because of its simplicity the exhaust system usually receives but little attention once it is installed; however, to obtain the best results, it should be inspected at suitable intervals and necessary adjustments made. The exhaust fan should be given proper attention the same as any other high-speed machine. It should be kept in proper alignment and tightly bolted to its foundation. Suction hoods, which have been removed to adjust the machines, should be replaced as soon as the adjustments are completed. Never start a machine with the blast gate closed, as the slight air leakage past the blast gate may draw material into the pipe and clog it. Disconnect furnace feeders from the furnaces when not in operation, and do not overload the system by ill-advised additions. CLOTHING FACTORY PRESSING ROOMS In the men's garment manufacturing industry there are used large batteries of. clothes pressing machines. These usually have large heated areas filled with high pressure steam, and the heaters and the piping which serves them and the jets of steam used on some of the machines for direct application to the cloth, bring about a man-cooling problem of considerable extent. The following solution has been found reasonably satisfactory for use during warm weather: 1. Mechanical exhaust ventilation of about 2,000 cu ft per minute per machine, with gravity inlets through ducts, doors, windows, etc. 357