- Describe, with the aid of sketches, the operating principle of an axial variable delivery hydraulic pump.(10)
What is an axial variable delivery hydraulic pump?
An axial variable delivery hydraulic pump is a type of hydraulic pump that uses multiple pistons arranged parallel to the axis of rotation (hence, “axial”) to generate hydraulic pressure and flow. The key feature of a variable delivery pump is its ability to adjust the volume of fluid it displaces with each revolution, thereby controlling the flow rate delivered to the hydraulic system.
Key Components & Operating Principle:
- Cylinder Block/Barrel: This rotating component houses the pistons and is driven by the input shaft.
- Pistons: Several pistons are arranged in a circular array within the cylinder block.
- Swash Plate: This angled plate is the heart of the variable displacement mechanism. The pistons are connected to the swash plate, and their stroke length (and hence, the pump’s displacement) is determined by the angle of this plate.
- Valve Plate: A stationary plate with inlet and outlet ports that control the flow of fluid into and out of the pump.
- Control Mechanism: This can be manual, hydraulic, or electronic, and it adjusts the swash plate angle to vary the pump’s output flow.
How it Works:
- Suction Stroke: As the cylinder block rotates, the pistons are drawn outwards due to the angled swash plate, creating a vacuum in their chambers. This draws hydraulic fluid into the piston chambers through the inlet ports on the valve plate.
- Discharge Stroke: As the pistons continue to rotate, they are pushed inwards by the swash plate, compressing the fluid and forcing it out through the outlet ports on the valve plate at high pressure.
- Variable Displacement: By changing the swash plate angle, the piston stroke length is altered. A larger angle results in a longer stroke, higher displacement, and greater flow output. A smaller angle leads to the opposite.
Advantages:
- Efficiency: By matching the flow output to the system demand, they minimize energy waste and reduce heat generation.
- Control: They offer precise control over flow and pressure, enabling smooth operation and response to varying load conditions.
- Compact: These pumps tend to be compact compared to other high-pressure pumps, saving space in installations.
Disadvantages:
- Complexity: They are more complex than fixed displacement pumps, leading to higher costs and potential maintenance challenges.
- Contamination Sensitivity: They are more sensitive to contamination in the hydraulic fluid, which can cause wear and damage.
Applications:
- Construction and Industrial Machinery: Where precise control of hydraulic power is needed for various functions like lifting, digging, or pressing.
- Marine Applications: Used for steering systems, winches, cranes, and other hydraulically powered deck machinery.
- Agricultural Equipment: Found in tractors, harvesters, and other machinery where variable flow and pressure are required.
In essence, axial variable delivery hydraulic pumps are a versatile and efficient solution for applications requiring dynamic control of hydraulic power.
Operation of an axial variable delivery hydraulic pump
Core Principle:
- At its heart, this pump utilizes multiple pistons aligned parallel to its rotating axis. These pistons reciprocate (move back and forth) within a cylinder block, drawing in fluid on one stroke and expelling it under pressure on the other.
Variable Displacement Mechanism:
- The key lies in the swash plate, an angled plate that the pistons’ shoes or slippers ride against.
- By altering the swash plate’s angle, we directly change the pistons’ stroke length.
- Steeper angle = longer stroke = more fluid displaced per revolution = higher flow output
- Shallower angle = shorter stroke = less fluid displaced = lower flow output
- At zero angle (parallel to the axis), there’s no piston movement, hence zero flow.
Operational Cycle:
- Suction:
- As the cylinder block (barrel) rotates, the pistons are pulled outwards due to the swash plate’s angle.
- This creates a vacuum within each piston’s chamber.
- Fluid is drawn in through inlet ports on a stationary valve plate, filling these chambers.
- Compression & Discharge:
- Continuing the rotation, the swash plate now forces the pistons inwards.
- This compresses the trapped fluid.
- High-pressure fluid is expelled through outlet ports on the valve plate.
- Continuous Flow:
- Multiple pistons work in a phased sequence, ensuring a smooth, continuous flow rather than pulsed output.
Control Methods for Varying Delivery:
- Manual: A simple lever or handwheel directly adjusts the swash plate angle.
- Hydraulic: Pressure signals from the system actuate a piston or mechanism to change the angle.
- Electronic: Sophisticated systems use sensors and electro-hydraulic valves for precise, automated control based on system demands.
Benefits of Variable Delivery:
- Efficiency: The pump only delivers what the system needs, reducing energy wastage and heat generation.
- Precise Control: Flow and pressure can be finely tuned to suit the application’s requirements, leading to smoother operation.
Points to Note:
- These pumps are generally more complex than fixed-displacement ones, requiring specialized knowledge for maintenance.
- They can be sensitive to contamination in the hydraulic fluid, demanding good filtration.
- Despite their complexity, they’re prized for their efficiency and controllability in applications where those factors are paramount.