6.5 Some applications of hydraulic systems

Reminders and uses:

Hydraulic machines use liquid fluid power to perform light or heavy work in many situations.

Heavy construction/demolition/digging vehicles are a common examples (illustrated below).

In these machines, hydraulic fluid is pumped to various hydraulic motors and hydraulic cylinders throughout the machine and becomes pressurized sufficiently to overcome resistance and effect movement.

The fluid is controlled directly or automatically by control valves and distributed through tubes/pipes.

Hydraulic systems, like pneumatic systems, are based on the fact that any pressure applied to a fluid inside a closed system will transmit that pressure equally everywhere and in all directions.

To be effective in transmitting force, hydraulic systems must use an in-compressible liquid as its fluid, rather than a compressible gas.

The wide-spread use of hydraulic machinery is because large amounts of power that can be transferred mechanically, and relatively simply, through small tubes and flexible hoses to achieve movement e.g. lifting or digging.

 

(1) Hydraulic jack system for lifting vehicles in garages

Four hydraulic piston and cylinder systems are used to jack up the red van. The fluid can be oil or compressed air.

The Land Rover (left) and the red  van (right) both have hydraulic brake systems

Key for the 5 photographic diagrams:

S = suspension spring;  H = the pipe conveying the hydraulic brake fluid force.

D = the brake drum and disc on which the brake pads in casing P are forced into contact with the smooth disc by the hydraulic transmitted force when you press the brake pedal.

A conveys speed of rotation information for the correct functioning of the advanced ABS braking

 system.

How does the hydraulic brake system of a motor vehicle work?

When you press on the brake pedal of motor vehicle, the force is transmitted through the brake fluid liquid by a pipe system (in modern cars it is aided by an electric pump system).

The braking mechanism involves several pistons and cylinders, known as the master cylinder (activated by the pedal) and slave cylinders on the brake drums (4 of the latter in the case of 4 wheeled vehicles).

The transmitted force pushes the brake pads onto the brake disc on the brake drum and the resulting friction reduces the speed of the vehicle.

When you take you foot off the brake pedal, the force is no longer transmitted and springs move the brake pads away from the brake discs to avoid unnecessary friction.

 

'Hydraulic' photographs by courtesy of Mark Raw of M T R Autotech Ltd garage, Castleton, North Yorkshire, England

 

(2) Plant machinery - examples of using hydraulic machinery

A huge range of excavators ('diggers'), diggers, bulldozers, elevated work platforms are used on demolition sites, construction sites use liquid power in hydraulic systems.

In the above photographs you can see the shiny steel systems of the hydraulic systems.

Using SEARCH some initial results may be ad links you can ignore - look for docbrown

Index physics Forces notes 6. Forces & pressure in fluids, calculations