In the variable-displacement construction (Figure 3-22 a yoke with an external control is used to change the angle.
As a result, the spool lifts, allowing nec vt47 manual pdf fluid to flow into the stroking cylinder.If the pressure falls off, the spool automatically moves back, oil is discharged from the piston to the inside of the pump casing, and the spring returns the yoke to a greater angle.The control consists of a compensator valve balanced between load pressure and the force of a spring, a piston controlled by the valve to move the yoke, and a yoke return spring.30 degrees maximum angle.As pressure builds, it acts against the end of the valve spool.While the piston moves from position 2 to position 3, the open end of the cylinder passes over the solid part of the pintle; therefore, there is no intake or discharge of fluid.Thus, the adjustment determines the displacement of the pump.The stroke length is controlled by the swash plate angle.The cylinder blow in this pump is turned by the drive shaft.Referring to view A of Figure 3-13, assume that space X in one of the cylinders of the cylinder block contains fluid and that the respective piston of this cylinder is at position.
The compensator adjusts the pump outlet to whatever displacement is required to develop and maintain the preset pressure.
In Figure 3-13, view B, the piston has reached position 2 and has forced the fluid out of the open end of the cylinder, through the outlet above the pintle and into the system.
Two basic designs are radial and axial, both are available as fixed- or variable-displacement models.When the pressure is high enough to overcome the valve spring, the spool is displaced and oil enters the yoke piston.The cylinder block is attached to the drive shaft.A variation of the inline piston design is the wobble plate pump.Wobble Plate Inline Pumps.Fluid enters the cylinder as the piston travels from position 1 to position 2 and is discharged from the cylinder as the piston travels from position 3 to position.View B shows the yoke moving down as system pressure drops below that required to overcome the compensator spring force.Manual control by a handwheel is the simplest.During this time the open end of the cylinder is open to the intake side of the pintle and fills with fluid.After the piston has passed the pintle and starts toward position 2, another discharge of fluid takes place.If the rotor is moved so that its center point is the same as that of the cylinder block, as shown in Figure 3-13, view C, there is no pumping action.View D shows this arrangement.
As the plate turns, it wobbles and pushes against spring-loaded pistons to force them to reciprocate.
Separate inlet and outlet check valves are required because the cylinders do not move past the ports.