How Hydraulic Systems Work: Principles, Components, and Applications

Hydraulic systems allow modern machinery to work in high-force applications with precision control. Using incompressible fluid to transfer energy, hydraulics power everything from industrial machines to construction equipment. In this post, Control Gear answers the question, ‘How does a hydraulic system work?’ and explains the principles it uses and its main components.

How Does a Hydraulic System Work?

A hydraulic system converts mechanical energy into hydraulic energy and back into mechanical energy. In straightforward terms (if you want to explain it to your kids), a hydraulic system is like two syringes connected by a tube filled with water. When you press the plunger on one syringe, it pushes the water through the tube. The water cannot be compressed, so it moves and pushes the plunger on the other syringe. This is how hydraulic systems work – they use liquid to transmit force and make things move!

Here is the process:

1. Input Force

When mechanical energy is applied, the hydraulic pump pressurises and converts the fluid into hydraulic energy.

2. Fluid Movement

Pressurised hydraulic fluid – usually hydraulic oil – moves through pipes or hoses. Because of its incompressibility and lubricating properties, hydraulic oil ensures energy transfer.

3. Control Mechanisms

Control valves direct the fluid flow and pressure. Three main types of control valves are used:

• Directional control valves guide the fluid to specific components.
• Pressure relief valves prevent excessive pressure.
• Flow control valves control the speed of fluid movement.

4. Hydraulic Actuators

The fluid reaches an actuator (hydraulic cylinder or motor), and the actuator converts hydraulic energy into mechanical energy for lifting, rotating, or pressing.

5. Return Path

Finally, the fluid flows back to a reservoir where it is filtered, cooled, and prepared for re-circulation.

Hydraulic System Principles

All types of hydraulic systems use basic fluid mechanics principles:

Principle	Description
Pascal’s Law	Pressure applied at any point in a confined fluid is transmitted equally in all directions. This allows force multiplication; a small input force can produce a large output.
Incompressibility of Fluids	Hydraulic oils are nearly incompressible, so force and motion are transferred consistently.
Energy Conservation	Energy is not lost but transformed –  mechanical energy becomes hydraulic energy and vice versa.
Flow Continuity	The fluid entering and exiting the system is constant, with no losses.
Pressure-Force	Force is calculated by pressure multiplied by surface area: F(N) = P(Pa) x A(m2). This determines how much work hydraulic cylinders or motors can do.
Friction and Energy Loss	Viscosity and pipe resistance cause hydraulic fluid power (energy) loss. Proper system design minimises these losses.
Temperature Effects	Hydraulic fluid properties like viscosity change with temperature.
Pressure and Flow Control	Valves control the system for safety, efficiency, and precision.
Leverage and Efficiency	Hydraulic systems adjust fluid paths and piston sizes to get a mechanical advantage.

Hydraulic System Components

Hydraulic systems consist of basic components. Each does its part to make everything work smoothly:

• Hydraulic Pumps convert mechanical energy into hydraulic energy by pressurising the fluid. The main types of hydraulic pumps are gear pumps, vane pumps, and piston pumps.
  
• Hydraulic fluid transmits power to the machine. It also lubricates, cools, and seals the system.
  
• Hydraulic reservoirs store the fluid, allow contaminants to settle, and accommodate thermal expansion.
  
• Valves help control pressure and direct the flow of the hydraulic fluid.
  
• Actuators control linear motion for lifting or pressing, and hydraulic motors control rotary motion for gears or wheels.
  
• Pipes and hoses transport fluid throughout the hydraulics system and are designed to withstand high pressure.
  
• Filters protect hydraulic machines from damage by removing contaminants from the fluid.
  
• Seals and fittings guarantee leak-free operation at connection points.
  
• Accumulators store pressurised fluid for extra power or shock absorption.
  
• Coolers and heaters manage fluid temperature for optimal performance.
  

Hydraulic System Applications

Many types of hydraulic systems are used in:

• Industrial machinery for precision and power for heavy-duty equipment.
• Automotive brakes for reliable braking performance.
• Construction equipment such as cranes, loaders, and excavators.
• Aerospace applications such as landing gear and flight systems.

From lifting heavy loads to safety in cars, hydraulic systems are everywhere.

Open-Loop vs Closed-Loop Hydraulic Systems

Hydraulics convert mechanical energy into hydraulic fluid power so that you can get a lot of work out of fluid pressure. Based on the flow of hydraulic oil, there are open-loop and closed-loop systems. Both use Pascal’s principle; pressure applied to an enclosed fluid is transmitted equally in all directions.

Open-Loop Systems	Closed-Loop Systems
Fluid flows from the reservoir through the system and back to the reservoir.	Fluid recirculates between pump and actuator without going back to the reservoir during operation.
How It Works	How It Works
Hydraulic oil pump moves fluid through valves and into actuators (e.g. hydraulic cylinders). After the work is done, the fluid returns to the reservoir.	Fluid flows through the hydraulic system continuously, powered by a variable displacement pump that adjusts fluid flow as needed.
Key Features	Key Features
Used in simple hydraulic systems for applications that require steady flow, like forklifts. Includes pressure relief valves to protect against excess hydraulic pressure. Transfers energy through a hydraulic system that works consistently.	High-performance systems with precise control for heavy equipment. Minimal hydraulic energy loss. Designed for high-pressure applications.

Which one is right for you?

Both use hydraulic pressure to power actuators but serve different purposes:

 • Open-loop systems are simple, reliable, and designed for steady loads.
• Closed-loop systems are efficient and precise for advanced equipment.

Hydraulic Systems Advantages and Disadvantages

Because hydraulics work by converting mechanical power to hydraulic power, they can do heavy work. Hydraulic systems are based on the principles developed by French mathematician Blaise Pascal. But what are the pros and cons of hydraulics?

Advantages

• High Power Output – Hydraulics generate power to raise heavy loads or apply high force.
  
• Smooth and Precise Control – Hydraulic systems allow fluid flow and pressure to be controlled to adjust to delicate tasks or maintain steady and stable operation.
  
• Versatility – There are many applications where hydraulics are used, from construction equipment to aircraft manufacturing.
  
• Safety Features – Relief valves avoid system overload and relieve pressure when needed.
  
• Compact Design – Hydraulic energy’s ‘small footprint’ offers a compact, practical solution for applications requiring efficiency.
  

Disadvantages

• Leakage Risk – Fluids can leak from the reservoir, which reduces efficiency and causes environmental concerns.
  
• Heat Generation – Hydraulic systems create heat when fluid flows through them, which can affect the system’s performance if not controlled.
  
• Maintenance Needs – Although systems are designed to work efficiently, they require regular maintenance to prevent them from wearing out, contaminating fluid, or decreasing pressure.
  
• Dependency on Fluids – Fluid behaviour must be uninterrupted; otherwise, the operation may be compromised by air bubbles or blockages.
  
• Sensitivity to Temperature – Changes in the properties of hydraulic oil with temperature necessitate the use of coolers or heaters for optimal operation.
  

Control Gear can provide expert advice on choosing the best type of hydraulic equipment for your specific needs. Contact us today to learn more about hydraulics and how they can benefit your business!