- Describe, with the aid of sketches, the operating principle of an axial variable delivery hydraulic pump.(10)
Here’s a clear, exam-style answer for you. I’ll explain the operating principle first, then outline the sketches you should reproduce in your notes.
Operating Principle of an Axial Variable Delivery Hydraulic Pump
1. General Arrangement
- The pump consists of a cylinder block (barrel) rotating with the drive shaft.
- Inside the barrel are pistons arranged axially (parallel to the shaft).
- A swash plate (or tilting plate) is mounted at an angle to the shaft.
- A valve plate (port plate) directs flow to suction and discharge ports.
2. Operation
- As the shaft rotates, the angled swash plate forces the pistons to reciprocate inside the barrel.
- During piston retraction, fluid is drawn in (suction stroke).
- During piston extension, fluid is forced out (delivery stroke).
3. Variable Delivery Principle
- Flow is varied by altering the angle of the swash plate:
- Large angle → long piston stroke → high displacement (maximum delivery).
- Smaller angle → short piston stroke → reduced displacement (reduced delivery).
- Zero angle (swash plate perpendicular to shaft) → pistons do not reciprocate → zero delivery.
- Adjustment of swash plate angle is achieved by a servo piston or control mechanism, which may be operated manually, hydraulically, or automatically in response to system pressure (load-sensing).
4. Advantages
- Provides variable flow while the pump runs at constant speed.
- Energy efficient, as output matches demand.
- Can act as a hydraulic motor if reversed.
Sketch Guidance (what to draw in exam)
- Sketch 1: Pump at maximum swash plate angle
- Show drive shaft, cylinder block, pistons sliding in and out, swash plate angled.
- Label suction and delivery ports with arrows for fluid flow.
- Sketch 2: Pump at reduced angle / zero angle
- Show swash plate nearly vertical, piston stroke reduced to zero.
- Indicate that no fluid is displaced at zero angle.