Document 3JBRJ58Xm7Z0Mnq6wQk1xdexD

HEATING VENTILATINC AIR CONDITIONING GUIDE 1941 oxygen in the second by potassium pyrogallate, and carbon monoxide in the third by cuprous chloride. A known volume of gas is drawn in, and after each of the three absorptions the reduced volume is again measured in the burette. Pressure and temperature of the gas sample are kept constant while measuring. Several passes are made through each pipette which contains tubes or glass beads to increase the wetted surface. It is essential that each reaction be completed before the next reaction is started. Since the life of the reagents is limited, it is well to keep a record of the number of samples tested. Care is needed in operation to prevent the pulling of reagents out of the pipettes into the capillary tubing and burette. Many recording gas analyzers are available and are usually found in the larger plants. SMOKE DENSITY MEASUREMENTS A common method of determining the relative density of smoke issuing from chimneys is by visual comparison with the Ringelmann Smoke Charts. A sheet of four ruled charts with varying weights of black lines is used. The sheet is 12 by 26 in. over all on which are four charts, each consisting of 294 squares, 14 wide and 21 high. The width of line and spacings is given in Table 1. Number of Card Table 1. Ringelmann Smoke Chart Spacings ------------ --------- ------------------------ Thickness of LINES, MM Distance in Clear Between Lines, mm i 1.0 2 2.3 3 3.7 4 5.5 .9.0 7.7 6.3 4.5 The charts are placed 50 ft from the observer and in line with the stack to be observed. At this distance the lines disappear and the charts appear as varying shades of gray. At times a white chart is added as No. 0 to the left of the four charts 1 to 4, and a black chart to the right as No. 5. Apparatus using the photo-electric cell has been devised for recording smoke densities in large plants. CARBON MONOXIDE MEASUREMENT In garages and vehicular tunnels carbon monoxide is a constant potential danger. In small amounts it causes headaches and inefficiency, and in larger concentrations it causes collapse and death in rather short periods of exposure. A method of analyzing for carbon monoxide con centrations completes the oxidation of the carbon monoxide in a known volume of sample, in the presence of a catalyst. The heat resulting is measured by a thermocouple calibrated in parts per 10,000 of carbon monoxide27. 17A Carbon Monoxide Recorder, by S. H. Katz, D. A. Reynolds, H. W. Frevert and J. J. Bloomfield (U. S. Bureau of Mines, Technical Paper No. 355, 1926). 638 Chapter 35 MOTORS AND MOTOR CONTROLS Direct Current Motors, Alternating Current Motors/or Single Phase and Polyphase, Special Applications, Classification of Motors, Manual Control, Automatic Control, Pilot Controls, Direct Current Motor Control, Squirrel Cage Motor Control, Multispeed Motor Control, Slip Ring Motor Control, Single Phase Motor Control '"T'HE electric motor, available in many different types suitable for JL various services, is now the most widely used form of prime mover. The equipment for starting, controlling and protecting these motors varies with the type and with the functions it is desired to attain. Motors used for heating, ventilating and air conditioning applications may be divided into two general classifications as follows: 1. For use with direct current. 2. For use with alternating current. direct Current motors There are three types of direct current motors available: 1. Shunt Wound. 2. Compound Wound. 3. Series Wound. Shunt Wound motors, being suitable for application to fans, centrifugal pumps, or similar equipment where the amount of starting torque required is relatively small, are used for the majority of applications in the field of heating, ventilating and air conditioning. They may be used on recipro cating pumps and compressors, if started under unloaded conditions. Compound Wound motors are required for application to compressors, stokers, reciprocating pumps when started under loaded conditions, and also when applied to similar equipment where high starting torque is required. Whenever frequent starting makes high starting and accelerat ing torque desirable, or where sudden changes of load are encountered, compound wound motors are used. -- Series Wound motors find only limited application in a few special cases and are available in only a limited range of sizes. 639