PRINCIPLES OF NAVAL ENGINEERING 



ROTATING 



CfLINOER CONNECTING ROTATING 

 BARREL RODS SOCKET 



RING 



N0NR0TAT1NG 

 TILTING BOX 



f^ NEUTRAL POSITION 



TILTING BOX SET 

 AT AN ANGLE 



. TILTING BOX SET AT 

 C A GREATER ANGLE 



147.111 

 Figure 15-12. -Diagram showing how tilting box position affects position of pistons. 



ing upon the position of the piston in the cylin- 

 drical opening. The face of the cylinder barrel 

 bears against the valve plate, anonrotatingpiece 

 which has two semicircular ports, one for suc- 

 tion and one for discharge. When a piston is at 

 the top position, at the end of its suction stroke, 

 the port for that piston is over the top land'* on 

 the valve plate; when a piston is at the bottom 

 position, at the end of the discharge stroke, the 

 port is over the bottom land on the valve plate. 

 Figure 15-13 shows the ports in the face of the 

 cylinder barrel and the ports in the valve plate. 



When the _A end is used alone as a constant- 

 speed, variable-capacity pump, the tilting box 

 is often so designed that it can be tilted in one 

 direction only. In this case, the flow of the 

 pumped liquid is always in the same direction. 

 When the A end is used as part of an electro- 

 hydraulic system, however, the tilting box is 

 most commonly designed tobe tilted in either di- 

 rection; and in this case the flow of the pumped 

 liquid may be in either direction. Therefore, it 

 should be clear that the position of the tilting box 

 controls both the direction of flow and the amount 

 of flow. 



Figure 15-14 shows a cutaway view of an 

 axial-piston variable stroke pump. Note that this 

 particular pump is designed for reversible flow, 

 since the tilting box canbe tilted in either direc- 

 tion. 



The radial-piston variable stroke pump is 

 similar in general principle to the axial-piston 

 pump just described, but the arrangement of 

 component parts is somewhat different. In the 

 radial-piston pump, the cylinders are arranged 

 radially in a cylinder body that rotates around 

 a nonrotating central cylindrical valve. Each cyl- 

 inder communicates with horizontal ports in the 

 central cylindrical valve. Plungers or pistons 



FACE OF VALVE PLATE 



The term land refers to the space between ports. 



FACE OF CYLINDER 3ARREL 



147.112 

 Figure 15-13.— Suction and discharge ports in 

 face of cylinder barrel and in valve plate. 



which extend outward from each cylinder are 

 pinned at their outer ends to slippers which slide 

 around the inside of a rotating floating ring or 

 housing. 



402 



