Fluid power fundamentals and calculations

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.