PRINCIPLES OF NAVAL ENGINEERING 



comparatively great amount of time for main- 

 tenance, 



ELECTROHYDRAULIC ELEVATORS 



Many naval ships are equipped with electro- 

 hydraulic elevators which are used to handle 

 airplanes, bombs, freight, mines, torpedoes, 

 ammunition, and other material. Electrohydrau- 

 lic elevators may be divided into two general 

 types: the direct plunger lift and the plunger- 

 actuated wire rope lift. 



DIRECT PLUNGER LIFT ELEVATORS.- 

 The platform of the direct plunger lift type 

 elevator is raised and lowered by direct con- 

 nection under the platform, with one or more 

 vertical hydraulic rams. Oil from a high pres- 

 sure tank is directed into the ram during the 

 hoisting operation. Lowering is accomplished 

 by the oil being discharged from the rams into 

 a low pressure tank. Pressure is maintained 

 in the high pressure tank by means of two 

 electrical variable displacement pumps, which 

 take suction from the low pressure tank. One 

 of the pumps is capable of maintaining elevator 

 operation at reduced speed. Two electric sump 

 pumps keep the volume of oil in the pressure 

 system within specified limits. 



Special control valves (operated by pilot 

 valves or a motor) in the pressure and exhaust 

 lines regulate elevator speeds by varying the 

 amount of oil admitted to or discharged from 

 the rams. Positive stops and mechanical locks, 

 interlocked with the elevator control system, 

 enable the platform to be stopped, locked, and 

 held in position at deck level. An equalizer 

 system maintains the platform at uniform level 

 under conditions of unequal loading. Automatic 

 quick-closing valves in the oil line prevent an 

 unrestricted fall of the elevator. 



PLUNGER-ACTUATED WIRE ROPE LIFT 

 ELEVATORS.— The primary difference between 

 the direct plunger lift elevator and the plunger- 

 actuated wire rope lift elevator is that the 

 latter type is raised by wire rope fastened to 

 the platform at two or four symmetrically 

 located points. Most hydraulic airplane elevators 

 are of the plunger-actuated wire rope lift type. 

 The wire ropes in an airplane elevator, through 

 a series of sheaves, are actuated by a horizontal 

 hydraulic ram located beneath the hangar deck. 



Hydraulic bomb elevators differ from 

 plunger-actuated wire rope lift elevators in that 



the hoisting wire ropes are wound on drums 

 driven through reduction gears by the hydraulic 

 motor. Raising, lowering, or speed changes are 

 accomplished by varying the stroke of the 

 variable delivery pump through differential 

 gearing. Hydraulic accumulators are not used 

 with hydraulic bomb elevators, 



WINCHES 



A winch is a deck machine used for hoisting 

 or hauling loads. The main components of a 

 winch are a wire rope drum (or drums), a re- 

 duction gear train, and a power unit. Some 

 winches are provided with one or two gypsy 

 heads for handling manila or other fiber lines. 



Most ships constructed before World War II 

 were provided with steam-powered winches, a 

 few of which remain in naval service. During 

 World War II, Auxiliary ships were provided 

 with winches powered by either alternating or 

 direct-current electric motors. On modern 

 ships, a-c electric drive winches are used. 

 Figure 21-8 shows an a-c electric motor drive 

 winch. 



Where stepless speed control between zero 

 and design maximum is required, a variable 

 speed hydraulic transmission is included be- 

 tween the electric motor and the gear train on 

 the same bed frame. The variable speed hy- 

 draulic transmission consists of a variable 

 volume pump connected by high pressure tubing 

 to a hydraulic motor, which is usually of the 

 fixed-displacement type. The fluid output from 

 the pump passes through the motor and returns 

 to the pump in a closed circuit, and the speed of 

 the motor varies as the volume of fluid from the 

 pump varies. The speed and direction of rotation 

 of the motors are obtained through a manually 

 operated lever control at the pump or at a remote 

 station. Figure 21-9 shows a typical electro- 

 hydraulic winch. 



One type of steam-driven winch is illustrated 

 in figure 21-10. The winch illustrated is equipped 

 with two gypsy heads (1), one mounted at each 

 end of the main drive shaft, and a single hoist- 

 ing drum (10), The drum is provided with a 

 standard type of brake band (3) with a foot-oper- 

 ated control and ratchet lock. The winch is 

 driven by a two-cylinder, single-expansion, 

 double-acting reciprocating engine. The drive 

 is by means of a train of spur gears, A gear 

 shift is provided to give two drive speeds. 



The clutch mechanism consists of a sleeve 

 (11) which is keyed to the crankshaft (12) and 



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