Fluid power fundamentals and calculations

Fluid Power Fundamentals

Fluid power is the use of fluids under pressure to generate, control, and transmit power.
Fluid power systems include hydraulic (liquid) and pneumatic (gas, usually air) systems.
In a fluid power system, the fluid in a closed system is pressurised and transmitted through tubes or hoses to create motion.
Pascal’s law states that a pressure change occurring anywhere in a confined incompressible fluid is transmitted throughout the fluid such that the same change occurs everywhere.
Key components of fluid power systems typically include a reservoir, a pump (or compressor for pneumatics), valves for direction, speed and pressure control, and actuators (like cylinders or motors that convert fluid power into mechanical power).

Fluid Properties

Density, viscosity, and bulk modulus are key properties impacting the behavior of fluids.
Density (ρ) is the mass of a substance per unit volume, typically measured in kilograms per cubic meter (kg/m^3).
Viscosity (μ) is a measure of a fluid’s resistance to shear stress or flow. It’s measured in pascal-seconds (Pa.s).
The bulk modulus (K) of a substance measures the substance’s resistance to uniform compression. It is given in units of pressure, usually gigapascals (GPa).

Fluid Power Calculations

The basic equation for pressure is: P = F/A, where P is pressure, F is force, and A is the area over which the force is distributed.
The flow rate Q of a pump is calculated using Q = V/t, where V is the volume and t is the time it takes for the volume to change.
The work done by a hydraulic/pneumatic cylinder can be calculated using W = F * d, where F is the force and d is the distance moved.
The power of a fluid power system can be calculated using P = W/t, where P is power, W is the work done, and t is the time it takes to do the work.
To calculate the fluid force acting on a surface, you can use F=PA, where F is the force, P is the pressure, and A is area.

Fluid Power Applications

Fluid power systems are used in a variety of engineering applications including vehicle systems (brakes, steering, lifts), industrial machines (presses, conveyors, lifts), and mobile equipment (construction, farming, marine).
They are also used in the control systems for automated machines and in safety and emergency systems.

Health and Safety

It’s important to remember that fluid power systems can be dangerous if not correctly installed, maintained and used.
Always follow the manufacturer’s instructions, workplace safety guidelines and use personal protective equipment where necessary.