What is a Hydrostatic Pump & How Does It Work?

Martin Wilson
May 30
3 min read

Hydraulic systems are widely used in industrial, agricultural, and construction applications. At the core of many of these systems lies a critical component: the hydrostatic pump. Whether you're a technician, engineer, or just curious about hydraulics, this blog offers a clear, in-depth, and user-friendly explanation of what a hydrostatic pump is and how it works.

What is a Hydrostatic Pump?

A hydrostatic pump is a positive displacement pump used in closed-loop hydraulic systems to convert mechanical energy into hydraulic energy. It pushes hydraulic fluid through a system under pressure, allowing that fluid to power motors, cylinders, or other actuators.

What makes a hydrostatic pump different from other hydraulic pumps is its ability to precisely control speed, direction, and torque—all while running in a closed circuit, recycling the fluid within the system.

How Does a Hydrostatic Pump Work?

To understand how a hydrostatic pump works, let's break it down step by step:

1. Mechanical Energy Input

The pump receives energy from an external power source, like a diesel engine or electric motor.

2. Fluid Movement

This mechanical energy drives internal components (like pistons or gears) to push hydraulic fluid into the system.

3. Pressure Creation

The pump builds fluid pressure inside a closed-loop circuit, which means the same fluid cycles between the pump and the actuator (motor or cylinder).

4. Hydraulic Power Transmission

The pressurized fluid moves through hoses to the hydraulic motor or actuator, where it's converted back into mechanical motion to perform work—like rotating a wheel or lifting a load.

5. Fluid Return

Once the work is done, the fluid flows back to the pump inlet, where the cycle repeats.

Closed-Loop System Advantage: Unlike open-loop systems where fluid returns to a reservoir, a hydrostatic pump reuses the same fluid repeatedly, improving efficiency and control.

Key Components of a Hydrostatic Pump System

Hydrostatic Pump – Converts mechanical input into pressurized fluid.
Hydraulic Motor or Cylinder – Uses the fluid’s pressure to produce mechanical motion.
Reservoir (Optional) – Maintains fluid supply and helps in cooling (in semi-closed systems).
Control Valves – Manage flow rate, pressure, and direction.
Filter Unit – Keeps fluid clean, preventing wear and system failures.

Types of Hydrostatic Pumps

1. Axial Piston Pumps

Pistons arranged in a circular pattern.
Adjustable swash plate controls flow and pressure.
Common in industrial and mobile machinery.

2. Bent-Axis Piston Pumps

Similar to axial pumps but offer higher efficiency and pressure ratings.
Ideal for compact equipment with variable speed demands.

3. Radial Piston Pumps

Pistons arranged radially around a central shaft.
High pressure, low-speed applications like presses and machine tools.

Advantages of Hydrostatic Pumps

Precise Speed and Direction Control
High Efficiency in Power Transmission
Compact and Space-Saving Design
Responsive Performance Under Load
Bidirectional Operation for Versatility

These benefits make hydrostatic pumps ideal for construction equipment (like skid steers and excavators), agricultural machinery, industrial conveyors, and more.

Applications of Hydrostatic Pumps

Industry	Use Cases
Construction	Skid steers, bulldozers, backhoes
Agriculture	Harvesters, tractors
Industrial	CNC machinery, presses
Aviation	Aircraft landing gear and control surfaces
Material Handling	Forklifts, mobile cranes

Maintenance Tips for Hydrostatic Pumps

Keeping your hydrostatic system in top shape is crucial. Here’s how:

Regularly Check Fluid Levels and Cleanliness
Inspect and Replace Filters
Monitor System Pressure and Temperature
Address Leaks Immediately
Use Manufacturer-Recommended Hydraulic Fluids

Why Choose Hydrostatic Pumps from Harvard Filtration?

At Harvard Filtration, we understand that system performance depends on more than just good hardware—it depends on clean, well-managed fluid.

Our filtration solutions are specifically engineered to protect sensitive components in hydrostatic systems by keeping your hydraulic fluid free from contaminants. This results in:

Longer pump and motor life
Reduced maintenance costs
Improved energy efficiency

Conclusion

Now that you know what a hydrostatic pump is and how it works, it's easy to see why it's such a vital component in modern hydraulic systems. It offers precision, power, and performance in a compact, reliable design. For maximum efficiency and longevity, pair your hydrostatic pump with high-quality filtration systems—and that's where Harvard Filtration can help.

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