. Electric railway journal . ct or sliding fits. No suctionvalves are used, thus eliminating one source of expensivemaintenance. Due to the high speed at which it is operatedthe over-all dimensions of the pump are small. The pumpsare made in sizes from 50 hp to 5000 hp in single larger sizes two units are mounted on opposite end?of an independent air-pump engine shaft. NEW AIR COMPRESSORS The General Electric Company is making a new motor-driven air compressor in three sizes for 600-volt service—the CP-27, CP-28 and CP-30, rated respectively at 15 , 25 cu. ft. and 35 cu. ft. pi
. Electric railway journal . ct or sliding fits. No suctionvalves are used, thus eliminating one source of expensivemaintenance. Due to the high speed at which it is operatedthe over-all dimensions of the pump are small. The pumpsare made in sizes from 50 hp to 5000 hp in single larger sizes two units are mounted on opposite end?of an independent air-pump engine shaft. NEW AIR COMPRESSORS The General Electric Company is making a new motor-driven air compressor in three sizes for 600-volt service—the CP-27, CP-28 and CP-30, rated respectively at 15 , 25 cu. ft. and 35 cu. ft. piston displacement. Whileprimarily designed for use on electric cars and locomotives,these compressors are equally suited for stationary workwhere an intermittent supply of compressed air is substantial frame casting completely encloses all workingparts and contains both the motor and crankshaft bolted to this casting is the motor frame, whichsimply supports the pole pieces and brush holders. The. ©» 4>~ <ISS» ®B3 Motor-Driven Air Compressor with the Covers Removed gear is in the center of the crankshaft, and as the gearingis entirely enclosed in the crankcase, a separate gearcaseis unnecessary. With this construction the dimensions ofthe motor are not limited by the distance between gear cen-ters, and therefore it is possible to design a motor withelectrical characteristics better suited for the service re-quired. Since the motor dimensions are not limited by me-chanical considerations, it is possible to use four salientpoles as in railway motors. Better commutation is thusobtained than is possible with the consequent pole con-struction necessary in former compressors. «■ The motor frame is an independent cylindrical steel cast-ing bolted to the compressor frame. Four laminated steelpole pieces are held to the frame by two bolts, the headsof which are outside the frame and readily accessible. Thetour field coils are held by spring stee
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