Piston Pumps

Piston pumps are a type of positive displacement hydraulic pump that uses one or more reciprocating pistons to move fluid. They are known for their high efficiency, ability to operate at very high pressures, and precise flow control, making them suitable for demanding hydraulic applications.

Types of Piston Pumps

Axial Piston Pumps:

Swashplate Type: Pistons are arranged axially (parallel) to the drive shaft. The swashplate is an angled plate against which the piston shoes ride. As the shaft rotates, the angle of the swashplate causes the pistons to reciprocate in their bores, drawing in and expelling fluid.

Fixed Displacement Swashplate: The swashplate angle is constant, providing a fixed flow rate per revolution.

Variable Displacement Swashplate: The swashplate angle can be changed (e.g., mechanically, hydraulically, or electronically), allowing for adjustment of the pump's output flow. This is crucial for energy efficiency.

Bent Axis Type: The cylinder block containing the pistons is set at an angle to the drive shaft. As the drive shaft rotates, the angle causes the pistons to reciprocate. Similar to swashplate types, they can be fixed or variable displacement. Generally more robust and can handle higher pressures.

Radial Piston Pumps:

Pistons are arranged radially around a central eccentric cam or shaft. As the shaft rotates, the eccentricity causes the pistons to move in and out of their bores, pumping fluid.

Often used for high-pressure, low-flow applications or as multi-outlet pumps.

Can be fixed or variable displacement.

Applications in Various Industries

Construction Heavy Equipment: Excavators, bulldozers, large cranes, concrete pumps use axial piston pumps for their main hydraulic circuits due to the need for high pressure, high flow, and precise control.

Industrial Machinery: High-pressure hydraulic presses, injection molding machines, die-casting machines, machine tools (e.g., CNC machines for clamping and tool changing), paper manufacturing equipment.

Aerospace Industry: Landing gear actuation, flight control systems, braking systems, where precision, high power density, and reliability under extreme conditions are critical.

Marine and Offshore: Steering gear, deck cranes, winches, thrusters, and drilling equipment on offshore platforms.

Mining Equipment: Large hydraulic shovels, drills, and support systems.

Agricultural Machinery: Large tractors, harvesters, and specialized implements requiring high hydraulic power.

Renewable Energy: Pitch control systems in wind turbines.

Test Benches: For hydraulic component testing due to their precise flow and pressure control.

Material Selection Considerations

• Cylinder Block: High-strength cast iron or ductile iron for rigidity, strength, and vibration damping.
• Pistons: High-strength, hardened steel, often with a smooth, wear-resistant surface finish.
• Swashplate/Cam Ring: Hardened alloy steels, often with a highly polished surface to minimize friction.
• Piston Shoes/Slippers: Typically bronze or a babbitt-type material to provide a low-friction interface with the swashplate.
• Drive Shaft: High-strength alloy steel, heat-treated for torsional strength and wear resistance at bearing journals.
• Bearings: High-capacity ball or roller bearings to support radial and axial loads. Hydrostatic bearings are also used for extremely high-pressure applications.
• Valve Plate/Port Plate: Hardened steel or cast iron, ground and lapped for precise sealing and minimal leakage.
• Seals: High-performance elastomers (e.g., Viton for high temperature and chemical resistance, Nitrile for general purpose) or PTFE for piston seals, shaft seals, and O-rings, ensuring compatibility with hydraulic fluid and operating conditions.
• Housing: Cast iron or aluminum alloy (for lighter applications).
• Fasteners: High-strength steel bolts and nuts.
• Coatings/Surface Treatments: Hard chrome plating, nitriding, or other surface treatments applied to critical wear surfaces to enhance durability and reduce friction.