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HYDRAULICS AN INTRODUCTION

HOW THE HYDRAULIC SYSTEM WORKS

The simple diagram shown above shall help to understand the working of the hydraulic system in a more graphic manner. The name hydraulic comes from a greek word "hydro" meaning water & "aulous" meaning "pipe".
The study of Hydraulics deals with the use and characteristics of liquids. Since the beginning of time, man has used to ease his burden.
It was not however until the 17th century that the branch of hydraulics with which we are to be concerned first came into use.
Based upon a principle discovered by the French scientist "Pacsal" it relates to the use of confined fluids in transmitting power, multiplying force and modifying motions.

ADVANTAGES OF HYDRAULICS


1. Varible Speed
2. Reversible
3. Overload Protection
4. Small Packages
5. Can be stalled

Simply stated, Pascal's law says this

"Pressure applied on a confined fluid is transmitted undiminished in all directions, and acts with the equal force on equal areas, and at right angles to them." This percept explains why a full glass bottle will break if a stopper is forced into the already full chamber. Perhaps it was the very simplicity of Pascal's law that prevented men from realising its tremendous potential for some two centuries. Then in the early stages of the industrial revolution a British mechanic named Joseph Bramah utilised Pascal's discovery in developing a hydraulic press. Bramah's first hydraulic press used water as a transmitting medium. However the most common liquid used in the hydraulic system is the oil. Oil transmits power readily because it is only very slightly compressible. It is desirable because of its lubricating quality. The hydraulic fluid must lubricate most of the moving parts of the component. The hydraulic system is not a source of power. The power source is a prime mover such as an electric motor or an engine which drives the pump. It is the versatility of the hydraulic system which gives it advantages over other methods of transmitting power.

A hydraulic jack or for that matter any device using hydraulic power in its simplest possible shape consists of five fundamental components.

The hydraulic RESERVOIR storing the hydraulic oil (oil is used as the medium to transmit force and motion-such fluids are called hydraulic oils) should be thoroughly clean, whether integrally built-in or used as a separate tank. PUMP, either of the integral or the remote control type, comprises of highly precision engineered pump plunger, cylinder, suction and delivery valves, safety valves with conical or steel balls matched with micron tolerances. Very often O Rings and special seals are used, made from specially treated leather or synthetic nitrile rubber or Teflon or other modern substitutes for greater resistance to wear and sealing power. It is imperative that these must function at peak efficiency by regular cleaning and flushing of foreign particles which enter into the hydraulic system and may clog the delicate valves, damage the seals and affect the functioning of other elements in the hydraulic circuit. A pump by itself would be useless without a system of VALVES to govern the flow of hydraulic oil to perform the desired function. The transmission of hydraulic oil from the reservoir by the pump through the valves to Ram & Cylinder which converts the hydraulic pressure into a mechanical force is by means of a HYDRAULIC CIRCUIT which is nothing but a network of passages in hydraulic systems. These passages are formed with the help of Steel Tubes, Flexible Hydraulic Hoses or through internal holes or cavities in metal blocks. It is of the utmost importance that the circuit is always leak proof as well as free from obstacles. Each joint or coupling must be securely tightened or replaced forthwith. No air lock or foreign particles should be allowed to interrupt or block the free flow of hydraulic oil. All Hydraulic Cylinders consist of two basic elements-the outer housing is called the CYLINDER body and the inner sliding element is called the Ram (or piston or plunger) which actually converts the hydraulic pressure into mechanical force and transmits to the desired point for performing the function. The movement of Ram is always in line with cylinder under pressure. Hydraulic oil is pumped into the cylinder and as more and more oil is forced into the cylinder pressure builds up and when enough oil is forced into the cylinder the resultant pressure will cause the ram,plunger or piston to move and consequently lift, press, push, pull or bend any object as the case may be. The Ram and Cylinder are also precision engineered and mostly fitted with high quality seals which give it the necessary compression holding capacity and prevent leakages.

The five fundamental components already illustrated and described combined together perform the specified job by a synchronous follow through of their individual functions.

The release valve is closed tightly to ensure flow of oil frcm the pump to the cylinder only. As soon as the pump is operated oil is sucked in from the reservoir. As the pump plunger is raised up oil passes from all the reservoir into pump cylinder with the suction valve opening up to allow oil from reservoir to enter into pump cylinder. When the Pump Plunger is pressed down the delivery valve opens up to allow the passage of oil from the pump in to the cylinder at the same time the suction valve automatically closes to prevent oil returning to the reservoir. By repeating the above two operations successively more and more oil is pumped into the cylinder resulting in the generation of pressure by the action of the load being lifted. When the load is desired to be lowered, the pressure within the cylinder is released by operating the Release Valve. The oil flows back into the reservoir as shown in the diagram above. Due to neglect or other causes pressure within the system may continue to increase beyond the predetermined safe working limit. To prevent damage to the system a safety relief valve is located between the cylinder and the reservoir to release excessive pressure by the opening up to the safety valve and discharge of oil into the reservoir (very often the safety overload preventive relief valve is located in between the reservoir and the pump - the pump automatically cuts off without delivery of oil to the cylinder due to generation of excessive pressure within the pump)..