Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGROTATINGCfLINOER CONNECTING ROTATINGBARREL RODS SOCKETRINGf^N0NR0TAT1NGTILTING BOXNEUTRAL POSITIONTILTING BOX SETAT AN ANGLE. TILTING BOX SET ATC A GREATER ANGLE147.111Figure 15-12. -Diagram showing how tilting box position affects position of pistons.ing upon theposition of the piston in the cylindricalopening. The face of the cylinder barrelbears against the valve plate, anonrotatingpiecewhich has two semicircular ports, one for suctionand one for discharge. When a piston is atthe top position, at the end of its suction stroke,the port for that piston is over the top land'* onthe valve plate; when a piston is at the bottomposition, at the end of the discharge stroke, theport is over the bottom land on the valve plate.Figure 15-13 shows the ports in the face of thecylinder barrel and the ports in the valve plate.When the _A end is used alone as a constantspeed,variable-capacity pump, the tilting boxis often so designed that it can be tilted in onedirection only. In this case, the flow of thepumped liquid is always in the same direction.When the A end is used as part of an electrohydraulicsystem, however, the tilting box ismost commonly designed tobe tilted in either direction;and in this case the flow of the pumpedliquid may be in either direction. Therefore, itshould be clear that the position of the tilting boxcontrols both the direction of flow and the amountof flow.Figure 15-14 shows a cutaway view of anaxial-piston variable stroke pump. Note that thisparticular pump is designed for reversible flow,since the tilting box canbe tilted in either direction.The radial-piston variable stroke pump issimilar in general principle to the axial-pistonpump just described, but the arrangement ofcomponent parts is somewhat different. In theradial-piston pump, the cylinders are arrangedradially in a cylinder body that rotates arounda nonrotating central cylindrical valve. Each cylindercommunicates with horizontal ports in thecentral cylindrical valve. Plungers or pistonsThe term land refers to the space between ports.FACE OF VALVE PLATEFACE OF CYLINDER 3ARREL147.112Figure 15-13.— Suction and discharge ports inface of cylinder barrel and in valve plate.which extend outward from each cylinder arepinned at their outer ends to slippers which slidearound the inside of a rotating floating ring orhousing.402