Hydraulic system Basic - Maintenance of hydraulic system
Definition - A descriptive term for a system operated or moved by a fluid. The hydraulic jack, in which force is transmitted from a handle by means of a heavy oil, is probably the most familiar hydraulic device
Definition Of Hydraulic Machine
The machine in which force is transmitted by liquids under pressure is known as hydraulic machine.
Example: Hydraulic Brakes, Hydraulic Jack
Example: Hydraulic Brakes, Hydraulic Jack
Hydraulic Brakes
The brakes used for car are hydraulic brakes.
The above diagram describes the working principle of Hydraulic brake.
When the brake pedal is pressed, a piston force breaks fluid from one cylinder along a connecting pipe to another cylinder.There, the fluid pushes on another piston. This pushes a brake pad against a metal disc attached to the rotating wheel of the car.The friction slows the wheel.
More About Hydraulic Machines:
Liquids are generally incompressible (they cannot be compressed).
When liquid is trapped (closed in a container) and pressure is exerted, this pressure is transmitted to all parts of the liquid.
The force (or pressure) is exerted on small area, but it results on a large area with much force.Thus the small force applied on a car brake results large force on 4 wheels.
When liquid is trapped (closed in a container) and pressure is exerted, this pressure is transmitted to all parts of the liquid.
The force (or pressure) is exerted on small area, but it results on a large area with much force.Thus the small force applied on a car brake results large force on 4 wheels.
Worked Example
The following system contains fluid
A downward force of 20 N is applied on the piston X.
What will be the upward pressure exerted by the liquid at Y.
What will be the upward pressure exerted by the liquid at Y.
- A. 4 N/Cm2
B. 1 N/Cm2
C. 20 N/Cm2
D. 40 N/Cm2
Correct answer is "B".
Complete hydraulic system guideline
What is a hydraulic system ?
A hydraulic system is a means of using a pressurised fluid to transmit power between the place where the power is generated and the point where it is used
What is hydraulic circuit
Part 2
INTRODUCTION
Hydraulic systems are extremely important to the operation of heavy equipment.
Hydraulic principles are used when designing hydraulic implement systems, steering
systems, brake systems, power assisted steering, power train systems and automatic
transmissions. An understanding of the basic hydraulic principles must be
accomplished before continuing into machine systems.
Hydraulics play a major role in mining, construction, agricultural and materials
handling equipment.
Hydraulics are used to operate implements to lift, push and move materials. It wasn’t
until the 1950s that hydraulics were widely used on earthmoving equipment. Since
then, this form of power has become standard to the operation of machinery.
In hydraulic systems, forces that are applied by the liquid are transmitted to a
mechanical mechanism. To understand how hydraulic systems operate, it is necessary
to understand the principles of hydraulics. Hydraulics is the study of liquids in motion
and pressure in pipes and cylinders.
WHY ARE HYDRAULIC SYSTEMS USED?
There are many reasons. Some of these are that hydraulic systems are versatile,
efficient and simple for the transmission of power. This is the hydraulic system’s job,
as it changes power from one form to another.
The science of hydraulics can be divided into two sciences:
„ Hydrodynamics
„ Hydrostatics
HYDRAULIC PRINCIPLES
There are several advantages for using a liquid:
1. Liquids conform to the shape of the container.
2. Liquids are practically incompressible.
3. Liquids apply pressure in all directions.
Liquids will conform to the shape of any container. Liquids will also flow in any
direction through lines and hoses of various sizes and shapes.
We have three oddly shaped containers shown in Figure 2, all connected together and
filled to the same level with liquid. The liquid has conformed to the shape of the containers.
A Liquid is Practically Incompressible
Hydraulic oil compresses approximately 1 - 1.5% at a pressure of 3000 psi (20,685
kPa). For machine hydraulic applications, hydraulic oil is considered as ideal and
doesn’t compress at all.When a substance is compressed, it takes up less space. A liquid occupies the sameamount of space or volume even when under pressure.Gas would be unsuitable for use in hydraulic systems because gas compresses and takes up less space
Fundamentals of Hydraulic Pumps
A hydraulic pump is a mechanical device that converts mechanical power into hydraulic energy. It generates flow with enough power to overcome pressure induced by the load.
When a hydraulic pump operates, it performs two functions. First, its mechanical action creates a vacuum at the pump inlet which allows atmospheric pressure to force liquid from the reservoir into the inlet line to the pump. Second, its mechanical action delivers this liquid to the pump outlet and forces it into the hydraulic system.
Classification of pumps
All pumps may be classified as either positive-displacement or non-positive-displacement. Most pumps used in hydraulic systems are positive-displacement.
A non-positive-displacement pump produces a continuous flow. However, because it does not provide a positive internal seal against slippage, its output varies considerably as pressure varies. Centrifugal and propeller pumps are examples of non-positive-displacement pumps.
A non-positive-displacement pump produces a continuous flow. However, because it does not provide a positive internal seal against slippage, its output varies considerably as pressure varies. Centrifugal and propeller pumps are examples of non-positive-displacement pumps.
Force = Pressure x Area.
This formula allows the Force to be determined and the Pressure and the Area when
two of the three are known.
P = Pressure = Force per unit of area.
The unit of measurement of pressure is the Pascal (Pa).
F = Force - which is the push or pull acting upon a body. Force is equal to the pressure
times the area (F = P x A).
Force is measured in Newtons (N).
A = Area - which is the extent of a surface. Sometimes the surface area is referred to
as effective area. The effective area is the total surface that is used to create a force in
the desired direction.
Area is measured in square metres (m2).
The surface area of a circle (as in a piston) is calculated with the formula:
Area = Pi (3.14) times radius-squared.
The pressure relief valve in the motor circuit
The diagram shows a hydraulic motor circuit; the direction of rotation of the motor is determined by the position of the 4/3-direction control valve. In the central position of the valve all ports are closed. After activating the left side of the valve, the hydraulic motor starts rotating in the pointed direction.
Generally in hydraulic systems the moment of inertia of the driven load is of a considerable level, so at the moment the 4/3-direction control valve is pushed in the central position the hydraulic motor starts acting as a pump, driven by the load. This will cause a tremendous increase of pressure at the right side of the hydraulic 'motor' and if there was no safety valve, the weakest component would break down or explode! In this system however the pressure relief valve will open and the oil flows back to the left side of the hydraulic motor. Because of the pressure at the right side of the motor the speed of rotation decreases to 0 rpm.
The hydraulic motor has an external leakage line so there will disappear oil from the motorcircuit. This may cause cavitation at the left side of the motor. In this system however the circuit is protected against cavitation by the check valves (suction valves).
The diagram on this page forms a basic diagram for most motor circuits.
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