Fluid power 101

Fluid power is just what the name says: fluids generate or transmit power to where it’s needed.

Specifically, fluid power is divided into hydraulics and pneumatics technologies:

• Hydraulics: the fluid is generally a liquid, usually oil or water
• Pneumatics: the fluid is generally a gas, typically compressed air. Other gases, such as nitrogen or argon, can also be used, but the expense of producing and processing these gases usually precludes their use

Fluid power systems

Are used in a variety of applications from braking systems on cars to robotics to heavy machinery and other machines. These systems produce linear motion using either hydraulic or pneumatic cylinders. Compare fluid power with two other methods of power transmission, electrical and mechanical, which usually need a mechanical device or other devices to convert rotational motion to linear motion.

Fluid power’s cylinders are compact, fitting smaller spaces, yet they have high-energy potential. Typically, fluid power systems use valves to control direction, speed, force and torque, and these control elements operate the system to achieve the desired motion.

The advantages of hydraulics and pneumatics

Hydraulics	Pneumatics
High power-to-weight ratio	Inexpensive
High torque at low speed	Lightweight
Ability to hold torque constant	Simple control systems
Ruggedness	Clean & non-reactive in magnetic environments
Reliability	Speed and precision

Note: Pneumatic systems are limited in the maximum pressure they can handle compared to hydraulics, making them suitable mainly for low-pressure applications.

Perhaps the best-known application of Pascal’s law is the hydraulic press:

A force F1 is applied to a small piston of area A1. The pressure is transmitted through a liquid to a larger piston of area A2. Since the pressure is the same on both sides, we see that P = F1/A1 = F2/A2. Therefore, the force F2 is larger than F1 by multiplying factor A2/A1. In a hydraulic press, a pump—driven by a prime mover such as an electric motor powered by electricity—creates the necessary pressure in the system. The application of force results in a specific volume of fluid being displaced, which is determined by the size of the pistons involved.

Hydraulic circuits are designed for controlling and regulating the flow and pressure within the system, ensuring that the movement and force are precisely controlled. Hydraulic systems are capable of generating high forces and rotary motion, making them ideal for manufacturing processes where they act on work pieces, such as in stamping or forming operations. Filters are essential for maintaining fluid cleanliness, preventing leakage, and ensuring reliable operation of the hydraulic system. Examples of manufacturing processes using hydraulic systems include automated assembly lines and metal forming presses.

You’ll find this principle working in hydraulic brakes, car lifts, hydraulic jacks, and forklifts, for example.

Hydraulic brakes

Without hydraulics, pressing the brake pedal with your foot would not produce enough force to apply all four brakes hard enough to quickly stop. The brake system in your car is a hydraulic system that relies on key hydraulic components such as the master cylinder, brake lines, and brake calipers. These components work together to multiply force and transmit it where it’s needed, providing enhanced safety and reliable performance.

How it works:

• When you press on the brake pedal, you’re moving a lever that forces a piston into a long, narrow cylinder, which is filled with hydraulic fluid (usually glycol-ether, mineral oil or silicone-based).
• The piston plunges into the cylinder, squirting hydraulic fluid through a long, narrow pipe at the end.
• This pipe feeds into wider cylinders located next to the car’s four brakes.
• The braking force is carefully controlled by the hydraulic system, allowing for precise and safe operation.
• When force is applied, it multiplies, because the cylinders near the brakes are wider than the one near the brake pedal. The multiplied force is able to clamp the brakes and stop your car.

Preventing leakage in hydraulic brake systems is crucial for maintaining system integrity and ensuring safety, as any loss of fluid can reduce braking efficiency and lead to system failure. One of the key advantages of hydraulic brakes is their ability to provide consistent, controlled braking force, which greatly enhances the safety of your vehicle.

Top hydraulics markets

According to the National Fluid Power Association (NFPA), these are the markets that use hydraulics the most:

Construction machinery	24%
Agricultural machinery	14%
Automotive (including light trucks)	9%
Class 4-8 trucks (including vocational trucks)	6%
Material handling (including conveying)	6%
Oil & gas machinery	4%
Lawn & garden	4%

Examples of hydraulic systems in these markets include excavators and loaders in construction, tractors and harvesters in agriculture, and hydraulic lifts in automotive and material handling.

 

Hydraulics are also widely used in heavy industrial equipment in factories.

 

Heavy industrial equipment, such as excavators and cement mixers, often relies on hydraulic components like pumps, cylinders, and valves to create efficient and controllable hydraulic power systems. These hydraulic components are essential for the performance and effectiveness of machines in demanding applications.

How do pneumatics work?

Pneumatics work the same way hydraulics do, except that instead of liquids, power is transmitted by gases such as compressed air, nitrogen, or other inert gases. Pneumatic systems can use various gases depending on the application, and the choice of gas can impact system safety and performance.

• Typically, pneumatic systems use a continuous supply of compressed air, which is provided by a compressor, a type of pump. Pump selection is important to ensure the system meets the required pressure and flow needs.
• The compressor is driven by a prime mover, often an electric motor powered by electricity, which converts electrical energy into mechanical energy to operate the pump.
• The compressor sucks in air from its environment and stores it in a high-pressure tank known as a receiver, where the volume of air stored determines the system's capacity for rapid actuation.
• The compressed air feeds the system via pipes, valves, and other pneumatic components such as cylinders and filters.
• Filters are essential for maintaining system health, preventing contamination, and reducing leakage, which can affect efficiency and performance.
• An advantage to pneumatics is that air in the atmosphere is free and plentiful – you have an unlimited supply.
• Pneumatic systems are capable of rapid actuation and are valued for their safety, but they are limited in maximum pressure compared to hydraulic systems.

The designs of pneumatic-system components, including valves, cylinders, and filters, make them ideal for simple automatic controls, which is why they’re often used in automation and manufacturing processes. Efficiency and performance are key considerations in pneumatic system design, as is the ability to control and regulate air flow and pressure for precise operation. Pneumatic systems can be controlled using various control valves and mechanisms, allowing for both linear and rotary motion in actuators and motors.

Another place you’ll find pneumatic systems is in HVAC systems, where compressed air is used as a tool for communication:

• From a controller, compressed air flows through copper and plastic tubes to a control device, normally a damper or valve actuator.
• Control is based on sensors and the building’s thermostats that bleed or retain the line pressure, from sensor to control device to actuator.
• Each sensor reacts to changes in temperature, static pressure, humidity and other conditions.
• The sensors feed back in a control loop to open or close the actuator in order to maintain the control set point.
• The actuators, which contain diaphragms, act in sequence with the control signal.
• The building’s thermostat is connected to one or more air lines from the primary source of compressed air, and to a valve or other final device.

The process of pneumatic operation enables efficient, controlled movement in a variety of applications, including rotary motion in pneumatic motors. Examples of manufacturing processes and tools that use pneumatic systems include assembly lines, packaging machines, and pneumatic tools such as drills, grinders, and impact wrenches.

Top pneumatic markets

According to the NFPA, these markets rely on pneumatic components that are capable of precise control and efficient operation:

Class 4-8 trucks (including vocational trucks)	13%
Automotive (including light trucks)	5%
Food processing	4%
Medical equipment	4%
Packaging machinery	3%
Material handling (including conveying)	3%
Semiconductor	3%

Examples of pneumatic systems in these markets include automated packaging machines, medical devices using air-driven actuators, and material handling equipment that utilizes pneumatic cylinders and valves for movement and control.

 

Best practice & Advantages of Fluid Power

The NFPA recommends these practices to cut energy usage by nearly a third. Developing skills in maintaining and optimizing fluid power systems is essential for achieving these best practices. Safety is a key consideration, requiring proper maintenance and precautions to prevent accidents and ensure reliable operation. The use of filters is critical for maintaining fluid cleanliness and system longevity. Pump selection is important in system design to match system requirements and improve efficiency. System parameters must be controlled and controlling mechanisms, such as valves, are necessary for precise regulation. The process of system optimization involves evaluating and improving each stage for better performance. For example, using pressure reducing valves or optimizing air blow are best practices that illustrate effective fluid power management. Modern technology, such as servo valves and load-sensing pumps, enhances system performance and safety. Some systems are limited by design constraints, such as maximum pressure ratings. Considering the volume of fluid when sizing system components is also crucial for proper operation.

Hydraulics	Pneumatics
Effective flow control	Eliminating pressure drop
Smart use of accumulators	Repairing leaks
Pressure reducing valves	Reducing pressure
Load-sensing pumps	Evaluating plumbing and storage
Pressure compensated pumps	Optimizing air blow
Servo valves	Employing intermediate bore-size cylinders
Hydraulic power units vs. electric motors	Correctly sizing components
Eliminating parasitic losses

 

 

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