1.Describe, with the aid of sketches, how an axial piston pump can vary the volume of liquid it displaces.(10)
Axial Piston Pump – Principle of Operation
An axial piston pump consists of:
- A cylinder block (barrel) containing several pistons arranged parallel to the drive shaft (axially).
- A swash plate or tilting plate, against which the pistons slide as the cylinder block rotates.
- A valve plate or port plate, which directs flow to the suction and discharge ports.
As the shaft rotates:
- Pistons move axially (in and out of the cylinder block) due to the angle of the swash plate.
- This movement creates suction during piston retraction and discharge during piston extension.
How the Pump Varies Displacement
- Swash Plate Angle
- When the swash plate is set at an angle to the shaft, the pistons stroke in and out.
- The greater the angle, the longer the piston stroke, so more liquid is displaced per revolution.
- When the swash plate angle is reduced, stroke length shortens → less liquid is displaced.
- Neutral (Zero Displacement) Position
- If the swash plate is set perpendicular (90°) to the shaft, the pistons do not reciprocate.
- In this case, there is zero displacement even though the shaft rotates (useful for variable-displacement control).
- Variable Displacement Mechanism
- The swash plate is mounted on a pivot and can be adjusted by a servo piston or control actuator.
- This allows the pump to vary flow according to system demand.
Sketch Description (for exam diagram)
- Labelled parts:
- Drive shaft
- Cylinder block with pistons
- Swash plate (show angled and neutral positions)
- Valve plate with suction and delivery ports
- Sketch 1 (angled swash plate): Pistons shown sliding in and out, arrows showing suction and discharge.
- Sketch 2 (neutral position): Swash plate vertical, pistons not reciprocating, no displacement.