Principles of naval engineering - Historic Naval Ships Association

Chapter 21. -OTHER AUXILIARY EQUIPMENTTURNCOMPONENTSOCKET RING83.82Figure 21-3.— Thrust and turning componentsin hydraulic motor operation.The development of this type of steering gearwas prompted primarily by the large momentaryelectric power requirements for electromechanicalsteering gears—particularly for ships oflarge displacement and high speed, with attendantincreased rudder torques.Electrohydraulic steering gears in use includevarious types of equipment. Some shipboardinstallations have double hydraulic ramsand cylinders; others have single-ram arrangements.(See figs. 21-4 and 21-6.)STEERING GEAR ARRANGEMENTS. -Onlythe pump of the previously described electrohydraulictransmission is used in electrohydraulicsteering gears. Axial-piston variable displacementpumps are used inmost installations;radial-piston pumps are used in some.The pumps are connected by piping to theram cylinders of the steering gear. Two pipesfrom each pump are united at a main transfervalve. The transfer valve is a multiportedvalve which permits the ram cylinders to beconnected to either pump while the pipes fromthe other pump are connected for bypassing.Various methods are used for connecting thehydraulic rams to the tiller. The arrangementsdepend on the design and on the space availablefor the installation. Two common arrangementsare shown in figures 21-4 and 21-6.Typical cruiser steering gear installationsinclude two rams set fore and aft, one on eitherside of the rudder stock. The rams operate therudder through a double yoke tiller fitted withsliding blocks.The gear illustrated in figure 21-6 is typicalof those installed on destroyers. The installationincludes a single ram set athwartship. The ramoperates the rudder through a single yoke tillerfitted with a sliding block.Some cruiser steering gear installations havetwo rams set fore and aft but located forwardfrom the rudder stock (fig. 21-4). The rams areconnected to the tiller by connecting links andpins. Some ships are equipped with twin ruddersand an independent steering gear for eachrudder. Carriers and auxiliary ships may haveany one of the above-mentioned steering geararrangements.PRINCIPLES OF OPERATION.—Regardlessof the type of equipment (double ram or singleram, axial pump or radial pump) included inelectrohydraulic steering installations, the principlesof operation are basically the same. Thedischarge volume and direction of flow from thevariable displacement pumps are controlled bythe operation of the tilting block in the pump.This control is accomplished mechanically bymeans of trick wheels in the steering gearroom, and by remote control from one or moresteering stations.Any movement, right or left, of the controlfrom any of the various steering stations placesthe hydraulic pump on stroke and causes thepump to supply liquid under pressure to thehydraulic rams, resulting in a correspondingright or left movement of the rudder. Thisrudder movement actuates the follow-up gearwhich in turn immediately acts to return thepump control to neutral but does not accomplishthis until the assigned rudder position has beenattained. The rudder is held in the assignedposition by a hydraulic lock until another movementis originated at the steering station.EMERGENCY STEERINGSYSTEMS.-Allnaval combatant and auxiliary ships equippedwith electrohydraulic steering gears are alsoequipped with an auxiliary steering gear. Thisemergency steering system generally consistsof a relief and shuttle valve, hand-operatedhydraulic pump, and the piping, valves, andfittings necessary to complete the system. Theemergency equipment is installed in or near thesteering gear compartment.523