How Does a Hydraulic Pump Work
At Union Hydraulics, we know that a hydraulic pump isn’t just a part—it’s the heart of any hydraulic system. Whether you're operating heavy equipment on a job site or managing a plant floor full of automation, understanding how hydraulic pumps work can help you make better decisions, avoid costly downtime, and extend the life of your machinery.
Let’s break down how hydraulic pumps operate, what types exist, and why they matter to the industries we proudly support.
Introduction to Hydraulic Systems
Hydraulic systems are the backbone of countless machines and industrial processes, using the power of pressurized fluid to transmit energy and perform work. At the center of every hydraulic system is the hydraulic pump, which converts mechanical energy—often from an electric motor or engine—into hydraulic energy. This transformation allows the system to generate the pressurized fluid needed to move, lift, or control heavy loads with precision and efficiency. Hydraulic pumps are essential for creating the flow and pressure that drive everything from construction equipment to manufacturing lines. Understanding how a hydraulic pump operates and its role within hydraulic systems is key to designing, maintaining, and optimizing reliable, high-performance machinery.
What Exactly Is a Hydraulic Pump?
In the simplest terms, a hydraulic pump converts mechanical power (such as rotation from a motor or engine) into hydraulic energy by turning it into fluid power. This fluid power—pressurized hydraulic oil—is what makes your equipment move, lift, push, dig, or drill. Without it, your hydraulic system doesn’t work.
Here at Union Hydraulics, we work with all kinds of pumps daily. Whether it’s a gear pump in a skid steer or a piston pump in a press machine, they all serve the same purpose: moving hydraulic fluid to where it’s needed—efficiently and reliably.
The Basics: How a Hydraulic Pump Operates
A hydraulic pump works by creating a vacuum at the pump inlet, specifically within the inlet chamber, pulling fluid from a reservoir. Atmospheric pressure then pushes fluid into the pump through the inlet chamber. That fluid is then pushed to the pump outlet before entering the system under pressure. While the pump itself doesn’t create pressure, it does generate flow—pressure builds only when there’s resistance to that flow (like when you’re lifting a heavy load).
This core function is what powers cylinders, motors, and valves in a wide range of applications. From construction to agriculture to manufacturing, hydraulic pumps are everywhere.
Positive vs. Non-Positive Displacement
Most of the pumps we deal with at Union Hydraulics fall under one of two categories:
- Positive Displacement Pumps – These move a fixed amount of fluid with each cycle. They’re the most common in mobile and industrial equipment because they’re consistent, efficient, and reliable. Positive displacement pumps can be of fixed or variable displacement, and the displacement can be fixed or adjustable depending on the pump design.
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Non-Positive Displacement Pumps – These are less common in hydraulic systems and rely more on fluid velocity than pressure. You’ll see them more in applications like water circulation or cooling.
Positive displacement pumps deliver a set amount of fluid during each pumping cycle.
Fluid Flow: How the Magic Happens
In a positive displacement pump—like the ones we rebuild and test every day—fluid flow is generated by the pumping element through mechanical action. In these pumps, the displacement chamber changes volume to move fluid. For example:
- Piston Pumps: A piston pulls back, creating a vacuum, drawing in fluid, then pushes forward to send it out.
- Gear Pumps: Fluid is carried between the teeth of two gears and pushed through the system.
- Vane Pumps: Vanes inside a rotating rotor slide in and out of the pumping chamber, creating chambers that draw in and move fluid through the pump.
Every cycle, the mechanical action delivers a consistent amount of fluid, which helps maintain a steady and predictable system operation—something every operator appreciates when reliability matters most.
Inlet and Outlet Flow
Think of the inlet as the mouth of the pump—it draws in fluid from the tank through the inlet line. Inside, rotating parts move that fluid within the pump housing to the outlet, where it’s sent down the hydraulic line. If flow is blocked or restricted at the outlet, pressure builds up. That’s why we always stress proper setup, the relief valve as a critical safety component, and maintenance. High pressure without a path to flow can cause serious damage.
Pressure & Flow Control
Hydraulic pressure depends on the load the system is trying to move. So even though the pump generates flow, the system pressure is really determined by the job being done. In many hydraulic systems, system pressure is based on load demands and can be regulated up to a maximum pressure for safety and efficiency. That’s where pump design comes into play:
- Fixed Displacement Pumps: Fixed displacement pumps deliver a constant flow regardless of system load, which can lead to inefficiency when load demands are lower. They are simple and tough, but less efficient for changing loads.
- Variable Displacement Pumps: Variable displacement pumps can adjust their output to match system requirements, making them ideal for systems that demand efficiency and flexibility by varying flow based on need.
In advanced hydraulic systems, high-pressure fluid is generated and managed by pressure-compensated or load-sensing pumps to optimize efficiency and reduce waste. A flow control valve is often used to regulate flow rates and pressure drops within the hydraulic circuit, ensuring optimal power efficiency and load matching.
Many newer systems also use load-sensing or pressure-compensated pumps to get the most performance with the least wasted energy.
Control Valves and Hydraulic Energy
Control valves are essential components in hydraulic systems, responsible for directing and regulating the flow and pressure of hydraulic fluid throughout the circuit. By managing how and where hydraulic fluid moves, control valves enable precise control over actuators, such as cylinders and motors, and help maintain the desired speed and force for each application. The combination of flow and pressure—known as hydraulic energy—is what allows hydraulic systems to perform demanding tasks efficiently.
The effectiveness of hydraulic energy use depends on selecting the right control valves and ensuring they are properly integrated into the hydraulic system. Variable displacement pumps, including axial piston pumps and vane pumps, are often paired with advanced control valves to provide adjustable flow and pressure, maximizing system efficiency and performance. By carefully managing hydraulic energy with the right components, operators can achieve smooth, responsive, and reliable system operation.
Main Types of Hydraulic Pumps We Work With
Gear Pumps
Reliable and rugged, gear pumps are popular because of their simplicity. Many modern gear pumps use helical gear teeth, which allow for quieter and smoother operation by enabling gears to mesh more efficiently. They’re perfect for moderate-pressure systems and can handle tough jobs without fuss. However, gears wear over time, causing the pump to gradually lose efficiency before any complete breakdown occurs. We see them often in compact machines and utility vehicles.
- Great for: simplicity, affordability, and ease of service
- Efficiency: up to 93% under ideal conditions
Piston Pumps
These are the powerhouses of the hydraulic world. They can handle high pressure and deliver variable flow. You’ll find them in large equipment like excavators, industrial presses, and injection molding machines.
- Types: The main variants are axial piston pumps, bent axis pumps, and radial piston pumps.
- The piston stroke in these pumps determines the displacement and overall performance, with adjustments made via mechanisms like the swashplate angle or eccentricity.
- In some designs, a control lever is used to adjust displacement or flow by changing the eccentricity or swashplate position, allowing precise regulation under varying conditions.
- Flexibility: Ideal for high-demand, high-precision jobs
Vane Pumps
Known for smooth, quiet operation, vane pumps—specifically hydraulic vane pumps—are often used in indoor equipment and mobile machinery that requires mid-range pressure. In these pumps, centrifugal force keeps the vanes pressed tightly against the walls of the pumping chamber, ensuring efficient sealing and fluid movement. Their efficient design works best with thinner hydraulic fluids like oil or even water-based fluids.
- Great for: machine tools, automotive systems, and low-noise environments
Specialized Pump Options
Some applications require pumps designed for unique conditions:
- Screw Pumps – Excellent for high-viscosity fluids and quiet operation. A screw pump is an axial-flow gear pump with multiple rotors that move fluid linearly and quietly, making it ideal for low-pressure, high-volume applications. Used in lube systems and heavy industrial setups.
- Gerotor Pumps – Compact, efficient, and often found in power steering systems and low-pressure applications.
Hydraulic Cylinder and System Integration
Hydraulic cylinders are the workhorses of hydraulic systems, converting the energy stored in pressurized hydraulic fluid into powerful linear motion or force. For a hydraulic cylinder to operate at its best, it must be seamlessly integrated with other system components, such as pumps, control valves, and reservoirs.
The choice between fixed displacement pumps and variable displacement pumps, as well as careful consideration of pump displacement and fluid flow rates, directly impacts how effectively the hydraulic cylinder performs.
Proper system integration ensures that hydraulic cylinders receive the right amount of fluid at the correct pressure, allowing for smooth, controlled movement and optimal force output.
By paying close attention to the interaction between hydraulic cylinders and other system components, engineers and operators can design hydraulic systems that deliver reliable performance and meet the specific demands of each application.
How We Measure Pump Performance at Union Hydraulics
Performance isn’t just about pressure—it’s about efficiency. We look at two key measurements:
- Volumetric Efficiency – How much fluid actually gets pushed versus what the pump is supposed to deliver. Volumetric efficiency is typically measured at a given pump speed to assess consistency and performance.
- Mechanical Efficiency – How much energy is lost to friction, heat, or leaks inside the pump. Pump speed directly affects both volumetric and mechanical efficiency.
Oil flow and fluid flows are key indicators of pump efficiency and overall hydraulic system health. Evaluating these flows at a given pump speed helps us understand how well the pump and system are operating.
Understanding these helps us diagnose problems, suggest the right replacements, or fine-tune your system for better performance.
System Design and Optimization
Designing and optimizing a hydraulic system involves more than just selecting the right pump or cylinder—it requires a holistic approach that considers every system component, the properties of the hydraulic fluid, and the expected operating conditions.
The goal is to create a hydraulic system that meets performance requirements while minimizing energy consumption and reducing the risk of component failure. This can be achieved by choosing efficient pump and motor combinations, sizing components appropriately, and ensuring compatibility between all parts of the system.
Modern design tools, such as simulation software and modeling programs, allow engineers to test different configurations and predict system behavior before building physical prototypes.
By leveraging these tools and focusing on system optimization, it’s possible to develop hydraulic systems that are both powerful and efficient, delivering long-term reliability and cost savings.
Where Hydraulic Pumps Are Used
Hydraulic pumps are vital across industries and are integral to the operation of the entire hydraulic circuit, ensuring efficient movement and control of hydraulic fluid. Here’s where you’ll find them working hard:
Construction
From excavators to lift trucks, hydraulic pumps power the heavy lifting and movement. When reliability matters on muddy job sites and tight deadlines, the right pump makes all the difference.
Manufacturing
Presses, clamps, and conveyors—all depend on hydraulic power. Precision is everything here, and pumps need to deliver consistent flow under variable loads.
Agricultural Equipment
Tractors, balers, harvesters—many run on hydraulic systems. Pumps here have to be tough, efficient, and able to handle dirt, dust, and long workdays.
Operator Control and Safety
Safe and effective operation of a hydraulic system depends on both the skill of the operator and the built-in safety features of the system. Operators must be properly trained to use the system controls, recognize warning signs, and respond quickly to any issues that arise.
Safety devices such as relief valves and pressure sensors are critical for preventing excessive pressure buildup, which can lead to equipment damage or hazardous situations. Adhering to established safety protocols and using personal protective equipment further reduces the risk of injury during operation and maintenance.
Regular inspection and maintenance of the hydraulic system helps ensure that all components, including pumps and valves, continue to function safely and efficiently.
By prioritizing operator control and safety, businesses can protect their personnel, extend equipment life, and maintain smooth, trouble-free hydraulic system operation.
Maintenance Tips from the Union Hydraulics Team
Want to extend the life of your hydraulic pump? Here’s what we recommend:
- Keep fluid clean and at proper levels - Dirty fluid causes wear, overheating, and system failure.
- Inspect seals, hoses, and fittings regularly - Small leaks can become big problems fast.
- Watch for unusual noises or heat - These often signal internal issues like cavitation or worn components.
- Change filters on schedule - It’s one of the easiest and most effective ways to protect your system.
- Perform regular maintenance - Routine checks help ensure your pump can overcome pressure induced by demanding system loads.
Need help diagnosing a pump issue? We’re just a phone call away.
Final Thoughts
At Union Hydraulics, we’ve built our reputation on helping customers understand, repair, and optimize their hydraulic systems—starting with the pump. Whether you're troubleshooting an old unit, planning a new build, or just looking for expert advice, we’re here to help.
A well-selected, well-maintained hydraulic pump keeps your system running smoothly, your machines working longer, and your business moving forward.
Frequently Asked Questions
What does a hydraulic pump do?
It converts mechanical energy into fluid power by moving hydraulic oil through your system.
What types of hydraulic pumps are most common?
Gear, piston, and vane pumps—each suited for different needs depending on pressure, flow, and application.
How does it create flow?
Through positive displacement. The pump traps and moves a fixed amount of fluid every cycle. It acts on a confined fluid, transmitting pressure through an incompressible liquid contained in a closed environment.
Why is maintenance important?
It prevents breakdowns, protects components, and extends the life of your equipment.
What affects pump efficiency?
Fluid type, temperature, internal wear, and how well the system is designed and maintained.
