Hydraulic Power

basics

Pascal’s Law

Pressure exerted at any point on

a confined liquid is transmitted

undiminished in all directions.

Pascal's law

Hydraulic Terms

Hydraulic Piston Shaft PSI

Pneumatic Stroke Check valve Spool valve

Pump Seal Rockshaft Cylinder

Hydraulic motor

Single-acting Double-acting Input / Output

Hydraulic

Tool or equipment powered by the movement of fluid under pressure. Examples are brakes, jacks & tractor lifts.

Pneumatic

Tool or equipment powered or supported by the movement of compressed air.

PSIPounds per Square Inch

determines amount of force

GPMGallons per Minute

determines speed of action

Pressure applied to piston “A” is transferred equally to a piston of the same size “B” because PSI is the same throughout the system.

Basic principle

If the surface area of piston “B” is 10 times the surface area of piston “A”, then the force applied to piston “A” is multiplied 10 times as the force exerted on piston “B”. PSI is equal throughout the system.

hydraulic advantage

Input / Output

Force input on a hydraulic system or component results in transfer of power to output of force by the system or component.

Pump

Functions in a hydraulic system by pressurizing and moving fluid from one part of the system to another.

Hydraulic pumps are usually one of four types:

PISTONGEARVANE

INTERNAL ROTOR

Piston Pumps

• Work well at PSI’s of 2000 or more• Single piston pump used in bottle jacks• Require several pistons working together to

generate enough volume for tractor applications

• Necessarily involve many moving parts

Gear Pumps• Work well at 1500 PSI and

below• Work with a minimum of

moving parts• Less expensive to

manufacture than piston type pumps

Gear Pump driven gear

idler gear

Hydraulic Motor

Receives power from moving fluid to transfer hydraulic power to mechanical rotating force.

Cylinder

Piece of equipment that transfers hydraulic power into mechanical movement in one or two directions only.

Hydraulic Cylinder

Single-actingRefers to a hydraulic cylinder that works in one direction only.

Double-actingRefers to a hydraulic cylinder that pushes and pulls.

Single-acting cylinder

Double-acting Cylinder

Piston

Internal component of a hydraulic cylinder that is moved in a linear motion by the action of fluid introduced into the cylinder.

Shaft

The polished round bar that is extended from and retracted into a hydraulic cylinder.

Stroke

The length of movement that a hydraulic cylinder is capable of producing.

Seal

Found in hydraulic components; function is to keep fluid from leaking between moving and non-moving parts

Check Valve

Restricts flow of fluid to only one direction; allows pressure to build up or be maintained.

Spool Valve

Controls direction of flow of fluid in a hydraulic system to cause the different parts of the system to function.

The first hydraulic power lift for a tractor was introduced in 1935 by John Deere. This unit only had two positions, up and down, but the hydraulic action cushioned the lowering of the implement.

Rockshaft

Rotating shaft on a modern tractor powered by an internal hydraulic cylinder; used to transfer power to the implement lift.

Hydraulic System of Tractor

INTRODUCTION

Normally, a hydraulic system with reference to a tractor is considered to be a unit responsible for lifting and lowering an agricultural implement.The draft control and weight transfer has become an inevitable function of the hydraulic system.In the hydraulic system the fluid is confined inside pipe lines, reservoir and cylinders. When pressure is applied at any point, the force is transferred by the fluid throughout the system which is utilized to lift the implements and do other jobs with minimum of effort.

The reason for selecting the hydraulic system of power transfer is due to its merits over the mechanical means of power transfer which are enumerated below:The hydraulic system is simpler than the

mechanical linkage system because fluid power can be routed around corners with less problems.

The system is flexible enough, allow the point of application to move to any location with respect to the source of power generation, which is almost constant in the case of the mechanical system.

Power can be engaged or disengaged with ease using a simpler control valve.

In comparison to input heavy forces can be controlled simply by increasing the size of the cylinder.

Because of self lubrication, wear and tear is less and hence the system is economical to operate.

A good range of speed of operation is possible.A hydraulic system is safer than a mechanical

system as the moving parts are minimized.Though the system is preferred but can’t be

called a perfect system without any drawbacks. The efficient operation require a regular cleanliness to avoid rusting, corrosion, dirt and other foreign materials.

Parts of hydraulic system

Hydraulic system fitted with the following basic components are: Reservoir Pump Relief valve Control valve Cylinder and piston Filter or strainer Operating lever Distributor Three point linkage

Reservoir

It is contains sufficient oil to move the piston for lifting the load.

Pump

It forces the fluid from the reservoir to the cylinder.

Relief Valve

It protect the system from high pressure. The valve is set for slightly higher than the working pressure. In case the pressure increase beyond the working pressure, the relief valve opens allowing the fluid to pass on the reservoir. Also when the piston reaches its extreme position, the relief valve opens to bypass the oil.

Control Valve

The control valve is used to allow the operator to direct the flow of fluid either from the pump to the cylinder or from the cylinder to the reservoir.

Cylinder

The cylinder convert the hydraulic power to mechanical power for doing the various jobs.

Hydraulic ValvesA hydraulic system is never complete without valves. These valves vary in shape and function, but ultimately control the circuit by regulating the pressure, direction and volume of oil flow. Based on their function, they can be divided into the following categories –1. Directional-control valves2. Pressure-control valves or safety valves3. Volume-control valves

Hydraulic system can be broadly divided into two major system –1. Open-centre-system2. Closed-centre system The open-centre-system uses a constant-

flow pump with an open-centre spool valve so that when oil is not flowing to the cylinder, it can pass onto the reservoirs.

In the case of the close-centre the pump is of variable flow type and the spool valve is close-centre type. In the neutral position the pump stops pumping oil.

Types of hydraulic system

Implement ControlThe tractor with a built-in lift system is connected to the implement through a specific type of mechanical linkage termed as three-point linkage and the system is known as mounted system. The implement is connected to the tractor hydraulic through three points – two bottom links and one top link. Both the bottom links are connected to two lift arms through lift links. The lift arms are directly mounted on a rock shaft which is further connected to the piston rod.

Any movement of the piston rod. Any movement of the piston is transferred to the bottom links. The top link is used for connecting the third hitch point of the implement and is adjustable for maintaining the implement level and suction angle. Load sensing for the draft control can also be done through the top link which is spring loaded. In some tractors the lower links are spring loaded for draft sensing. Depending upon the soil condition and type of operation the mounted implement can be controlled either by position control or draft control.

Continue

Position Control

The lever position on the quadrant directly represents the corresponding position or depth of the implement. Therefore in position control it is possible to present the working depth. Therefore normally the position control is used for weeders, planting and sowing machines, sprayers and for transportation of the implement.

Draft Control

Under this system of control, the implement is set for a particular draft (drawbar pull) rather than depth. In varied soil conditions the implement automatically takes more or less depth to maintain the predetermined draft. Most of the indigenous tractors possess a draft control system in addition to the position control.

Mixed Position and Draft Control

It is also possible in some Tractor (viz. HMT, Ford, etc) to suitable blend the response through an interlink mechanism so that a desired depth of ploughing is maintained within close limits and draft control too is allowed to function for better traction.

Maintenance and repair of hydraulic system

For successful operation of any hydraulic system, cleaning and periodic maintenance is very essential. If the operator is alert and keeps the machine clean, refills clean oil, replaces or clean the filter regularly, keeps the tubes and rubber hose tight and protects the system from dust and other contaminants, the system will undoubtedly work efficiently with less trouble.

Continuously

Most of the troubles arise because of dirty or improper grade of oil in use. Low oil level also is a cause of a number of troubles. Normally, the following defects may arise:1. System may not work at all.2. System may work slowly but fail to lift

under load.3. Sinking of load may take place.4. Cylinder movement may be jerky.5. System may get hot and foaming.

Continuously

While diagnosing the trouble, one should check whether system is defective due to the pump or some other component. If the pump is fitted outside, it can be observed and its sound can be listened to, but if it is fitted inside, the flow pressure can be checked at the delivery of the pump. The pump can either produce insufficient discharge or can create insufficient pressure. The reasons for low volume and low pressure are enumerated below.

ANY QUESTIONS

By:-Dd Singh, CIMTGovt. I.T.I Kurukshetra, HaryanaE-mail <ddsinghsanch@yahoo.co.in>Mob. +91-94164-49258

Thanks To All