hydraulics training

04/08/2023 04:23:16 PMBasic Hydraulic

HYDRAULICS

Objective of The Programm

Understand what is hydraulic Different components used in hydraulic Hydraulic symbol How to read hydraulic circuit

WHY HAUDRAULIC ?

Variable Speed Reversible Overload protection Small Packages Can Be Stalled Less Noisy

What is Hydraulic ?

The engineering science of liquid pressure and flow.

hydraulics is used for the generation, control, and transmission of power by the use of pressurized liquids

.This drive section consists of cylinders or hydraulic motors, depending on the application in question

The energy control section consists of the various valves used to provide control and regulate the flow rate, pressure and direction of the hydraulic fluid

The power supply section contains pump and drive motor and the components for the preparation of the hydraulic fluid

Pascal's law states that when there is an increase in pressure at any point in a confined fluid, there is an equal increase at every other point in the container.

Pascal's Principle and Hydraulics

How Hydraulic Works ?

Power transmission

If a force F1 is applied to an area A1 of a liquid, a pressure p results. If, as in this case, the pressure acts on a larger surface A2, then a larger counter-force F2 must be maintained. If A2 is three times as large as A1, then F2 will also be three times as large as F1.

Hydraulic power transmission is comparable to the mechanical law of levers.

04/08/2023 04:23:17 PM

Displacement transmission

If the input piston of the hydraulic press travels a distance s1, a volume of fluid will be displaced. This same volume displaces the output piston by the distance s2. If the area of this piston is larger than that of the input piston, the distance s2 will be shorter than s1.Hydraulic displacement transmission is comparable to the mechanical law of levers

Basic Hydraulic

Displacement transmission

The Energy transfer hereEqual 10 Kg X 10 Cm = 100 Kg Cm

The Energy transfer hereAlso is 100 Kg Cm (1 Cm X 100 Kg = 100 Kg Cm)

F = P X AF1 = 10 X 10 = 100

F2 = 10 X 100 = 1000

S1= 10 CmS2= 1 Cm

FORCE PRESSURE & AREA

HYDRAULIC POWER UNIT

The hydraulic power unit (power supply unit) provides the energy required for the hydraulic installation. Its most important components are the reservoir (tank) , drive (electric motor), hydraulic pump, pressure relief valve (safety valve), filter and cooler. The hydraulic power unit may also act as a carrier for other devices (gauges, directional control valves).

CIRCUIT SYMBOLS FOR ENERGY TRANSFERThe symbols shown

are used in circuit diagrams for energy transfer and hydraulic-fluid preparation.

In the interests of clarity, the lines in the circuit diagram should be drawn without cross-overs as far as possible.

CIRCUIT SYMBOLS FOR ENERGY TRANSFER

The direction of the arrows in the circuit symbols for the heater and cooler correspond to the direction of heat flow

HYDRAULIC FLUID FILTERS

SignificanceHydraulic systems need clean and uncontaminated fluid to operate properly. Contaminants

inadvertently introduced into the hydraulic system or metal debris from normal component wear can damage hydraulic components.

OperationA filter element traps solid particles while allowing fluid to pass through. Many filters also use a bypass

valve that allows fluid to flow through the filter housing without passing through the actual filter element. This allows the system to remain operational for some time, even if the filter is clogged.

Filters used to described by nominal & absolute rating in microns.A filter nominally rated as 10 microns, for example ,would trap most particle 10 microns in size or larger, The Filter absolute rating however would be somewhat heigher size ,perhaps 25 microns

CIRCUIT DIAGRAM: RETURN FLOW FILTERAn oil filter situated in

the return line to the tank has the advantage that the filter is thus easy to maintain. A disadvantage, however, is that contamination is removed from the hydraulic fluid only after it has passed through the hydraulic components.

This configuration is often used.

CIRCUIT DIAGRAM : PUMP INLET FILTER With this

configuration, the pump is protected from contamination. The filter is, on the other hand, less easily accessible.

If these filters have a too fine mesh, suction problems and cavitation effects may occur. Additional coarse filters upstream of the pump are recommended.

WATER COOLERWith this design of cooler, hydraulic fluid is fed through tubes over which coolant (water) flows. The heat which is discharged can be re-usedThe operating temperature in hydraulic installations should not

exceed 50 - 60ºC, since this would cause an

unacceptable reduction in viscosity, leading to premature

aging of the fluid. In comparison with air cooling,

operating costs a higher due to the required coolant and the susceptibility to corrosion. Temperature difference of up to approx. 35ºC can be handled

HEATING ELEMENT

Heaters are often required to ensure that the optimum operating temperature is reached quickly. Heating elements or flow preheaters are used for heating and pre-heating hydraulic fluid.

If the viscosity is to high, the resulting increase in friction and cavitation leads to greater wear.

CIRCUIT SYMBOLS FOR ENERGY CONVERSION

Hydraulic pumps are shown by a circle with a part representation of a drive shaft. Triangles in the circles show the direction of flow. The triangles are shown solid, since pressure fluid is used in hydraulics.

If the pressure medium is gaseous, as in the case of pneumatics, the triangles are shown in outline.

Hydraulic pumps should convert mechanical energy (torque ,speed ) into hydraulic

Energy

When choosing Pump following points must be taken in account

1. Operating medium2. Required rang of pressure3. Expected range of speed4. Minimum & Maximum operating temperature5. Installation6. Type of drive7. Expected life time8. Maximum Level of noise9. Ease of servicing10. possible given maximum cost

Power supply section

PUMPGear pumpsGear pumps (with external teeth) (fixed displacement) are simple and economical pumps. The swept volume or displacement of gear pumps for hydraulics will be between about 2 cm3 (0.002 liter) and 200 cm3 (0.2 liter). They have the lowest volumetric efficiency of all three basic pump types (gear, vane and piston pumps) These pumps create pressure through the meshing of the gear teeth, which forces fluid around the gears to pressurize the outlet side

Parameter Displacement volume : 0.02 to 200 cm3Max Pressure : Up to 300 Bar(Size Dependent)Rating Of speed : 500to 6000 RPM

INTERNAL GEAR PUMPHow Internal Gear Pumps Work

1. Liquid enters the suction port between the rotor (large exterior gear) and idler (small interior gear) teeth. The arrows indicate the direction of the pump and liquid.

2. Liquid travels through the pump between the teeth of the "gear-within-a-gear" principle. The crescent shape divides the liquid and acts as a seal between the suction and discharge ports.

3. The pump head is now nearly flooded, just prior to forcing the liquid out of the discharge port. Intermeshing gears of the idler and rotor form locked pockets for the liquid which assures volume control.

4. Rotor and idler teeth mesh completely to form a seal equidistant from the discharge and suction ports. This seal forces the liquid out of the discharge port.

Parameter Displacement Volume : 3 to 250Cm 3Operating Pressure: Up to 300 barRating Of Speed : 500 to 3000 RPM

PUMPRotary vane pumpsRotary vane pumps (fixed and simple adjustable displacement) have higher

efficiencies than gear pumps, but are also used for mid pressures up to 180 bars in general. Modern units can exceed 300 bars in continuous operation, although vane pumps are not regarded as "high pressure"

The simplest vane pump is a circular rotor rotating inside of a larger circular cavity. The centers of these two circles are offset, causing eccentricity. Vanes are allowed to slide into and out of the rotor and seal on all edges, creating vane chambers that do the pumping work. On the intake side of the pump, the vane chambers are increasing in volume. These increasing volume vane chambers are filled with fluid forced in by the inlet pressure. Inlet pressure is actually the pressure from the system being pumped, often just the atmosphere. On the discharge side of the pump, the vane chambers are decreasing in volume, forcing

PUMPScrew pumpsScrew pumps (fixed displacement) are a double Archimedes' screw, but closed. This

means that two screws are used in one body. The pumps are used for high flows and relatively low pressure (max 100 bar). They were used on board ships where the constant pressure hydraulic system was going through the whole ship, especially for the control of ball valves, but also for the steering gear and help drive systems. The advantage of the screw pumps is the low sound level of these pumps; the efficiency is not that high.

The major problem of screw pumps is the hydraulic reaction forces which is transmitted axially opposed to the flow direction,

Piston PumpAll Piston pump operate on principle of that a piston reciprocating in abore will drae fluid in as

it is retracted & expel it as it moves forward Two basic design is available

1. A radial piston pump piston arrange radially in cylinder block

2. Axial Piston pump piston in axial units are parallel to each other & to axis of the cylinder

Piston pumps are highly efficient unit ,available in a wide range of

capacities .They are capable of operating medium to high pressure range (1500-3000 psi)

Axial piston pump may be further divided in to inline(swash plate) & bent axis type

Radial piston pump

The outer ring for bracing of the pumping pistons is in eccentric position to the hollow shaft in the center. This eccentricity determines the stroke of the pumping piston.The piston starts in the inner dead center (IDC) with suction process. After a rotation angle of 180° it is finished and the workspace of the piston is filled with the to moved medium. The piston is now in the outer dead center (ODC). From this point on the piston displaces the previously sucked medium in the pressure channel of the pump.

Animation

RADIAL PISTON PUMP ANIMATION

Return

Axial piston pumpAn axial piston pump has a number of pistons (usually an odd

number) arranged in a circular array within a housing which is commonly referred to as a cylinder block, rotor or barrel. This cylinder block is driven to rotate about its axis of symmetry by an integral shaft that is, more or less, aligned with the pumping pistons (usually parallel but not necessarily).

Axial piston pumps using the swashplate principle

Like radial piston pump ,the displacement of axial piston pump s is determine by the size & number of piston ,as well as stroke length

In variable displacement model s of the inline pump ,the swash plate is installed in movable yokePivoting the yoke on pintled change the swash plate angle to increase or decrease the piston

strokeThe yoke can be positioned by any several means ,including manual control, pressure& load

sensing & pressure limiter control compensator control

Maximum angle on this unit is limited by construction to 17.5 degrees

Fix displacement Variable displacement

WOBBLE PLATE PISTON PUMP This pump has pistons in a stationary block, and a rotating wobble plate.

There might be 4, 5, or more pistons (usually an odd number are used) -- only two shown here.

Each piston has a valve within it and another valve behind it. Fluid comes in on the wobble plate side (on the bottom left in this drawing) and exits under pressure in the back (on the right here).

The pistons are pushed against the wobble plate with large springs. A pair of smaller springs force the valves (small metal balls) closed. The spring inside the piston is fairly weak, since only suction is used to force it open.

This type of pump can develop incredible pressure -- 10,000 P.S.I. or more. It is commonly used for low-volume applications. ergency fuel pumps on

some early aircraft.

PUMPBent Axis Pump.

Bent axis piston pumps have a rotating cylinder containing parallel pistons arranged radially around the cylinder centre line. The cylinder is driven by an shaft which is arranged at an angle to the cylinder axis. the shaft includes a flange with a mechanical connection to each piston. As the shaft rotates the pistons are made to reciprocate over a stroke based on the relative angle of the shaft and cylinder.

The displacement of this pump varies between 0 to 30 degree .Fix displacement model are usually availabe eith 23 to 30 degrees .In variable displacement ,yoke with externally control is used to change the angle ,with some control

CIRCUIT SYMBOLS FOR HYDRAULIC MOTORS

The symbols for hydraulic motors are distinguished from the symbols for hydraulic pumps by the fact that the arrows showing the direction of flow are the other way round.

HYDRAULIC MOTORSA hydraulic motor is a mechanical actuator that converts hydraulic pressure and flow into torque and

angular displacement (rotation). The hydraulic motor is the rotary counterpart of the hydraulic cylinder. Conceptually, a hydraulic motor should be interchangeable with a hydraulic pump because it performs the opposite function

It has to be part of a hydraulic circuit that incorporates a hydraulic pump along with other hydraulic gadgetry such as valves, filters, high-pressure hoses, metal tubing, hydraulic fluid reservoir etc.

The pump draws hydraulic fluid from the reservoir and supplies it under pressure to the hydraulic motor linked mechanically to the workload. The pump receives mechanical power for its operation through a prime mover that is either an internal combustion engine or an electric motor.

Where electric motors, which can deliver only rotational power and must be sized to suit the load application, hydraulic motors are much smaller in size even when the application involves heavy loads. In a heavy electromechanical system a big electric motor needs to be directly located on the motion axis which may not be always feasible

For the same application, a relatively small hydraulic motor can be placed with ease and connected to a pump located remotely within the system through an arrangement of high-pressure flexible hoses that can be conveniently routed even through disadvantageous twists and bends.

HYDRAULIC MOTOR APPLICATIONSDue to the high torque at low speeds, loaders and other construction equipment use heavy hydraulic

motors to drive the wheels for moving the machines around. There is one motor for each wheel and the diesel engine is used to drive the pump, which deliver hydraulic fluid to the motors. A hydraulic motor with the right specifications needs to be fitted to enable the machine to function properly.

1. Oil pipeline inspection equipment2. Undersea camera manipulation3. Jumbo jet maintenance jacks4. Milling and sawing applications5. Dynamite blast hole pump drive6. Automatic clamping7. Textile washing agitators8. Orange peeling machines9. Fan drives10. Diamond wheel dresser11. Drill and tap machine tool12. Chicken processing machinery13. Conveyor drives14. Electric motor coil winding

TYPES OF HYDRAULIC MOTORS Hydraulic motors delivering rotary power are mainly of two types and are classified on torque

and rotational speed. One is referred to as HSLT or High Speed Low Torque and the other as LSHT or Low Speed High Torque motor.

The LSHT motor can have a speed range from 0.1 to 1000 revolutions per minute whereas HSLT motor speeds can range from 1000 to 5000 revolutions per minute.

The size advantage can be gauged from the fact that the size of a 5hp hydraulic motor will be roughly that of a 350ml beer can. In addition, there would be very low level noise and vibration generation and much higher efficiency. HSLT and LSHT.

Hydraulic motors are available in different types

Piston

Radial

TYPES OF HYDRAULIC MOTORS

Gear type hydraulic motors

can be classified as internal gear or 'gerator' type and external gear motors. Gerator motors are very quiet in operation and designed to transmit rotary power through an output shaft connected to a rotor moving inside an outer stator. Supply of hydraulic fluid under pressure makes the rotor move eccentrically along the inner periphery of the stator. An external gear hydraulic motor has a set of meshing gears enclosed in a sealed housing have passages supply and return of hydraulic fluid. Pressurized hydraulic fluid flowing into the housing has an action on the gear teeth and makes the gears rotate. The rotational movement of the gears is transmitted to the workload through an output shaft connected to the rotating gears and passing through the motor housing.

Internal gear type (Gerator)

TYPES OF HYDRAULIC MOTORSA radial piston hydraulic motor

has a bank of cylinders arranged like a car engine with a series of pistons riding on cams along a camshaft, which is attached to the output shaft. The reciprocating movement of the pistons gives rotary movement to the camshaft/output shaft that is tapped for power. In another variation cylinders are arranged radially like that of an aircraft engine with the pistons moving inwards to push against a cam located in center causing it to rotate. The cam is mechanically linked to the output shaft/workload. Yet another type of radial piston hydraulic motor with cylinders placed radially like an aircraft engine has the pistons moving outwards to push against cams in a housing that surrounds the motor. This makes the housing rotate. The rotating housing is tapped for power. These motors are generally used as wheel motors and for other suitable applications like forklifts

They are available in displacements from 40cc/rev up to about 12 litres/revCrankshaft type Radial Piston Motors are capable of running at "creep" speeds and some can run

seamlessly up to 1500 rpm whilst offering virtually constant output Torque chacteristics. This makes them still the most versatile design.

Vane type hydraulic motors have movable vanes connected to a

centrally located output shaft. The whole arrangement is enclosed in a housing/ case that receives hydraulic fluid under pressure from the pump. This fluid exerts force of the vanes to make them move like fan blades. This action results in rotating the output shaft, which is tapped for power.

Axial piston motors

The axial piston motor is of the 'swashplate type' and has a bank of cylinders arranged in a circle (360 degrees) parallel to each other. Each cylinder has a piston, which reciprocates with one end of the piston pushing against an eccentric swash-plate located at one end of the bank of cylinders. There is a mechanical arrangement through which the eccentric plate is connected to an output shaft that is axially aligned with the cylinders. During motor operation, the cylinders are filled with high-pressure hydraulic fluid in a particular sequence making the pistons move outwards to push sequentially against the swash-plate causing it to rotate. On the return stroke of the piston the fluid is swept back at low pressure to return to a reservoir. The operation imparts rotational movement to the output shaft, of which one end is connected to the swash-plate and other to the workload. This is a design that caters to a very compact cylindrical hydraulic motor. Most axial hydraulic motors are HSLT.

CIRCUIT SYMBOLS FOR SINGLE ACTING CYLINDERS

Single acting cylinders have one port, i.e. pressure fluid can be applied only to the piston side. With these cylinders, the return stroke is produced either by external force, shown in the symbol by an opening bearing cap, or by a spring is shown within the symbol in this latter case.

CIRCUIT SYMBOLS FOR DOUBLE ACTING CYLINDERS

Double acting cylinders have two ports to allow pressure fluid to be applied to both cylinder chambers. The symbol for a differential cylinder is distinguished from the symbol for a double acting cylinder by the two lines added to the end of the piston rod. The area ratio is generally 2:1. In the case of cylinders with double- ended piston rods, the symbol shows that the piston areas are of equal size (synchronous cylinders

WHAT ARE HYDRAULIC CYLINDERS?

An actuation device that makes use of a pressurized hydraulic fluid is known as a hydraulic pump.

This mechanism is used for producing linear motion and force in applications that transfer power. In other words, a hydraulic cylinder converts the energy stored in the hydraulic fluid into a force used to move the cylinder in a linear direction.

BarrelPiston rod

Piston Seal

CYLINDER CUSHIONING

Cushioning of some sort normally is required to decelerate a cylinder's piston before it strikes the end cap. Reducing the piston velocity as it approaches the end cap lowers the stresses on cylinder components and reduces vibration transmitted to

PARTS OF A HYDRAULIC CYLINDERCylinder barrelThe cylinder barrel is mostly a seamless thick walled forged pipe that must be machined internally.

The cylinder barrel is ground and/or honed internallyCylinder base or capIn most hydraulic cylinders, the barrel and the bottom portion are welded together. This can damage

the inside of the barrel if done poorly. Therefore, some cylinder designs have a screwed or flanged connection from the cylinder end cap to the barrel. (See "Tie rod cylinder", below) In this type the barrel can be disassembled and repaired.

Cylinder headThe cylinder head is sometimes connected to the barrel with a sort of a simple lock (for simple

cylinders). In general, however, the connection is screwed or flanged. Flange connections are the best, but also the most expensive. A flange has to be welded to the pipe before machining. The advantage is that the connection is bolted and always simple to remove. For larger cylinder sizes, the disconnection of a screw with a diameter of 300 to 600 mm is a huge problem as well as the alignment during mounting.

PistonThe piston is a short, cylindrical metal component that separates the two parts of the cylinder barrel

internally. The piston is usually machined with grooves to fit elastomeric or metal seals. These seals are often O-rings, U-cups or cast iron rings. They prevent the pressurized hydraulic oil from passing by the piston to the chamber on the opposite side.

piston rodThe piston rod is typically a hard chrome-plated piece of cold-rolled steel which attaches to the piston

and extends from the cylinder through the rod-end head. In double rod-end cylinders, the actuator has a rod extending from both sides of the piston and out both ends of the barrel. The piston rod connects the hydraulic actuator to the machine component doing the work.

Rod glandThe cylinder head is fitted with seals to prevent the pressurized oil from leaking past the interface

between the rod and the head. This area is called the rod gland. It often has another seal called a rod wiper which prevents contaminants from entering the cylinder when the extended rod retracts back into the cylinder.

CLASSIFICATION OF CYLINDERS ACCORDING TO SPECIFICATIONS

Plunger Cylinders:

These cylinders are also known as Ram cylinders. These types of hydraulic cylinders are placed in an upright position. This is done so that once the supply of the fluid is stopped, the weight on the cylinder will make it return to its original position. The cylinders used in automobile service centers are a good example of the plunger cylinders.

Telescoping CylindersTelescopic cylinders are also known as multistage hydraulic cylinders. These cylinders have

at the most six stages. These are specially used in applications where there is less area. Telescopic cylinders can either be single action or double action. The stroke of these cylinders is long and is used in applications such as cranes and forklifts, etc.

Cable CylindersThe cable cylinders can either be hydraulic or pneumatic powered cylinders that are of the

double acting type. These cylinders have long strokes and produce moderate force. The cable cylinders can be operated in limited space.

Diaphragm CylindersDiaphragm cylinders are of two types i.e. flat diaphragm and rolling diaphragm. These

cylinders have zero leak around the piston.

CLASSIFICATION OF CYLINDERS ACCORDING TO FUNCTION

Single Acting Cylinders:In single acting cylinders the fluid is pressurized from only one side

of the cylinder during both the expansion as well as the retraction process. A spring or an external load is used to return the cylinder top to its original position i.e. when pressure of the fluid is cut off.

Double Acting CylindersIn the double acting cylinders, the pressure from the fluid is applied

in both the directions. Single cylinders that consist of springs are not used in large stroke applications because there are inherent mechanical problems associated with the spring. The double acting rods could be of two types:

• Single rod ended• Double rod ended

DIRECTION CONTROL VALVESDirection control valves are use in hydraulic system to

direct the flow of fluid in a desired direction & location in the circuit

There are two fundamental positions of directional control valve namely normal position where valve returns on removal of actuating force and other is working position which is position of a valve when actuating force is applied.

CIRCUIT SYMBOLS FOR DIRECTIONAL CONTROL VALVES

Designations for directional control valves always give firstly the number of ports and then the number of switching positions. Directional control valves always have at least two ports and at least two switching positions. The number of squares shows the number of possible switching positions of a valve. Arrows within the squares show the direction of flow. Lines shown how the ports are interconnected in the various switching positions of the valve. The designations always relate to the normal position of the valve

This illustration shows the circuit symbols for 4/2- and 5/2-way valves.

There are two general methods for the designation of ports, using either the letters P, T, R, A, B and L or consecutively using A, B, C, D etc.; the first method is the preferred one in the relevant standard

The illustration shows the circuit symbols for 4/3-way valves with various mid-positions

CIRCUIT SYMBOLS FOR MANUAL OPERATION

The switching position of a directional control valve can be changed by various actuation methods. The symbol for the valve is accordingly supplemented by a symbol indicating the actuation methods shown, such as pushbuttons and pedals, a spring is always necessary for resetting. Resetting can, however, also be achieved by actuating the valve a second time, for example in the case of valves with hand levers and detents.

CIRCUIT SYMBOLS FOR MECHANICAL ACTUATION

This illustration shows the symbols for stem or push button, spring and roller stem

CIRCUIT SYMBOL FOR PRESSURE VALVES Pressure valves are

represented using squares. The flow direction is indicated by an arrow. The valve ports can be designated as P (supply port) and T (tank return port) or as A and B. The position of the arrow within the square indicates whether the valve is normally open or normally closed. Adjustable pressure valves are indicated by a diagonal arrow through the spring. Pressure valves are divided into pressure relief valves and pressure regulators.

PRESSURE RELIEF VALVES

PRESSURE REDUCING VALVE

CIRCUIT SYMBOLS FOR FLOW CONTROL VALVES A distinction is made in flow

control valves between types which are affected by viscosity and those which are unaffected. Flow control valves unaffected by viscosity are termed orifices. A 2-way flow control valve consists of restrictors, one adjustable restrictor which is unaffected by viscosity (orifice) and a regulating restrictor (pressure compensator). These valves are represented by a rectangle containing the symbol for the adjustable restrictor and an arrow to represent the pressure compensator. The diagonal arrow through the rectangle indicates that the valve is adjustable.

CIRCUIT SYMBOLS FOR NON-RETURN VALVES

The symbol for non-return valves is a ball which is pressed against a seat. Delockable non-return valves are shown by a square containing the symbol for a non- return valve. The pilot control for unlocking the non- return valve is indicated by a broken line at the pilot port. The pilot port is designated by the letter X.

CIRCUIT SYMBOLS FOR MEASURING DEVICES

The illustration shows the symbols for measuring devices used in hydraulics

ACCUMLATOR

A hydraulic accumulator is a pressure storage reservoir in which a non-compressible hydraulic fluid is held under pressure by an external source. The external source can be a spring, a raised weight, or a compressed gas. An accumulator enables a hydraulic system to cope with extremes of demand using a less powerful pump, to respond more quickly to a temporary demand, and to smooth out pulsations. It is a type of energy storage device.

Compressed gas accumulators, also called hydro-pneumatic accumulators, are by far the most common type.

TYPES OF ACCUMULATORS

Towers Raised weight Compressed gas (or gas-charged)

closed accumulator Compressed gas open accumulator Spring type Metal bellows type

COMPRESSED GAS ACCUMULATOR

It is widely used accumulator in present scenario. It is popularly known as “hydro-pneumatic accumulator”. It apply force to the liquid by using a compressed gas that acts as the spring. It uses inert gas (nitrogen) under pressure that provides the compressive force on fluid. Oxygen is not used because oxygen and oil can form an explosive mixture when combined under pressure As the volume of the compressed gas changes the pressure of the gas, and pressure of the fluid, changes inversely.

BLADDER TYPE ACCUMULATORbladder accumulator consists of seamless high-

pressure cylinder with an internal elastomeric bladder with pressurized nitrogen on it and hydraulic fluid on the other(external) side. The accumulator is charged with nitrogen through a valve installed on the top. The accumulator will be pre-charged to nominal pressure when the pumps are not operating. The maximum flow rate of the accumulator is controlled by the opening orifice and the pressure difference across the opening. Bladder material widely used are epichlorohydric rubber(ECO) and Acrylonitrile butadiene rubber

ADVANTAGES : Fast acting Not susceptible to contamination Consists behavior under similar

conditionLIMITATIONS : Compressed ratio is limited, approximately

4:1 Bladder failure.(NBR).

PISTON TYPE ACCUMULATOR

This accumulator consists of a cylinder assembly, a piston assembly, and two end-cap assemblies. An accumulator contains a free-floating piston with liquid on one side of the piston and pre-charged air or nitrogen on the other side. An increase of liquid volume decreases the gas volume and increases gas pressure, which provides a work potential when the liquid is

allowed to dis-charged.ADVANTAGES : High compression ratio up to 10:1

Higher flow rate than bladder type.LIMITATIONS : They are more susceptible to fluid

contamination Lower response time than the bladder and diaphragm

METAL BELLOW ACCUMULATORThe metal bellows accumulator is

similar to bladder type, expect the elastic is replaced by a hermitically sealed welded metal bellows. Fluid may be internal or external to the bellows. Internal It is used when a fast response time is not critical, yet reliability is important. Metal bellow types are pre-charged by supplier and then permanently sealed leading to a maintenance free accumulator.

LIMITATIONS : Response time is more High cost External

SPRING TYPE ACCUMULATOR It uses the energy stored in

springs to create a constant force on the liquid contained in an adjacent ram assembly. The load characteristics of a spring are such that the energy storage depends on the force required to compress s spring. The free (uncompressed) length of a spring represents zero energy storage. As a spring is compressed to the maximum installed length, high pressure value of the liquid in a ram assembly is established. As liquid under pressure enters the ram cylinder, causing a spring to compress, the pressure on the liquid will rise because of the increased loading required to compress the spring.

FUNCTIONS OF ACCUMULATOR Emergency and safety: An accumulator which is kept

constantly under pressure is valuable in the event of an electrical power failure as it can provide flow and pressure to perform an additional function or complete a machine cycle.

Shock or pulsation dampening: An accumulator can be used to cushion the pressure spike from sudden valve closure, the pulsation from pumps or the load reaction from sudden movement of parts connected to hydraulic cylinders.

Leakage compensation: An accumulator can be used to maintain pressure and make-up for lost fluid due to internal leakage of system components including cylinders and valves.

Thermal expansion: An accumulator can absorb the pressure differences caused by temperature variations in a closed hydraulic system.

Noise reduction: An accumulator is effective at reducing hydraulic system noise caused by relief valves, pump pulsations, system shock and other circuit generated noises.

ACCUMLATOR SYMBOL

HYDEAULLIC HOSE

HYDRAULIC HOSEHydraulic tubes are seamless steel precision pipes, specially manufactured for hydraulics. The tubes have standard sizes for different pressure ranges, with standard diameters up to 100 mm. The tubes are supplied by manufacturers in lengths of 6 m, cleaned, oiled and plugged. The tubes are interconnected by different types of flanges (especially for the larger sizes and pressures), welding cones/nipples (with o-ring seal), several types of flare connection and by cut-rings. In larger sizes, hydraulic pipes are used. Direct joining of tubes by welding is not acceptable since the interior cannot be inspected.

Hydraulic pipe is used in case standard hydraulic tubes are not available. Generally these are used for low pressure. They can be connected by threaded connections, but usually by welds. Because of the larger diameters the pipe can usually be inspected internally after welding. Black pipe is non-galvanized and suitable for welding.

Hydraulic hose is graded by pressure, temperature, and fluid compatibility. Hoses are used when pipes or tubes can not be used, usually to provide flexibility for machine operation or maintenance. The hose is built up with rubber and steel layers. A rubber interior is surrounded by multiple layers of woven wire and rubber. The exterior is designed for abrasion resistance. The bend radius of hydraulic hose is carefully designed into the machine, since hose failures can be deadly, and violating the hose's minimum bend radius will cause failure. Hydraulic hoses generally have steel fittings swaged on the ends. The weakest part of the high pressure hose is the connection of the hose to the fitting. Another disadvantage of hoses is the shorter life of rubber which requires periodic replacement, usually at five to seven year intervals.

Tubes and pipes for hydraulic applications are internally oiled before the system is commissioned. Usually steel piping is painted outside. Where flare and other couplings are used, the paint is removed under the nut, and is a location where corrosion can begin. For this reason, in marine applications most piping is stainless steel.

HYDEAULLIC HOSE SAE 100R1 hose should be used with petroleum- and water-based

hydraulic fluids, within a temperature range from140° to 100° C. Type A consists of an inner tube of oil-resistant synthetic rubber, a

single wire braid reinforcement, and an oil- and weather-resistant synthetic rubber cover. A ply, or braid, of suitable material may be used over the inner tube or over the wire reinforcement (or both) to anchor the synthetic rubber to the wire.

Type AT has the same construction as Type A, except AT has a cover designed to assemble with fittings that do not require removal of the cover or any portion of it.

SAE 100R2 hose should be used with petroleum- and water-based hydraulic fluids, within a temperature range from140° to 100° C. It consists of an inner tube of oil-resistant synthetic rubber, steel-wire reinforcement according to hose type, as detailed below, and an oil- and weather-resistant synthetic rubber cover. A ply, or braid, of suitable material may be used over the inner tube and/or over the wire reinforcement to anchor the synthetic rubber to the wire.

Type A has two braids of wire reinforcement Type B has two spiral plies and one braid of reinforcement Type AT is the same as Type A, but AT has a cover designed to

assemble with fittings that do not require removal of the cover or any portion of it.

Type BT is the same as Type B, but BT has a cover designed to assemble with fittings that do not require removal of the cover or any portion of it.

HYDEAULLIC HOSE

SAE 100R3 hose should be used with petroleum- and water-based hydraulic fluids, within a temperature range from140° to 100° C. It is constructed with an inner tube of oil-resistant synthetic rubber, two braids of suitable textile yarn, and an oil- and weather-resistant synthetic rubber cover.

SAE 100R4 hose should be used in low pressure and vacuum applications, with petroleum- and water-based hydraulic fluids, within a temperature range from140° to 100° C. It is constructed with an inner tube of oil-resistant synthetic rubber, a reinforcement consisting of a ply, or plies, of woven or braided textile fibers with a suitable spiral of body wire, and an oil- and weather-resistant synthetic rubber cover.

HYDEAULLIC HOSE

SAE 100R5 hose should be used with petroleum- and water-based hydraulic fluids, within a temperature range from140° to 100° C. It is constructed with an inner tube of oil-resistant synthetic rubber reinforced with two textile braids separated by a high-tensile-strength steel-wire braid. All of the braids are impregnated with an oil- and mildew-resistant synthetic rubber compound.

SAE 100R6 hose (above) should be used with petroleum- and water-based hydraulic fluids within a temperature range from140° to 100° C. It consists of an inner tube of oil-resistant synthetic rubber, one braided ply of suitable textile yarn, and an oil- and weather-resistant synthetic rubber cover.

HYDEAULLIC HOSE SAE 100R7 thermoplastic hose (above)

should be used for synthetic, petroleum-, and water-based hydraulic fluids in a temperature range from140° to 93° C. It consists of a thermoplastic inner tube resistant to hydraulic fluids with suitable synthetic-fiber reinforcement and a hydraulic fluid- and weather-resistant thermoplastic cover. Nonconductive 100R7 is identified with an orange cover and appropriate lay line. Its pressure capacity is similar to that of 100R1.

SAE 100R8 hose is high-pressure thermoplastic hose that should be used with synthetic, petroleum- and water-based hydraulic fluids within a temperature range from140° to 93° C. It consists of a thermoplastic inner tube resistant to hydraulic fluids with suitable synthetic-fiber reinforcement and a hydraulic fluid- and weather-resistant thermoplastic cover. Nonconductive 100R8 is identified with an orange cover and appropriate lay line. Its pressure capacity is similar to that of 100R2.

SAE 100R9 hose should be used with petroleum- and water-based hydraulic fluids within a temperature range from 140° to 100° C.

Type A consists of an inner tube of oil-resistant synthetic rubber, four spiral plies of wire wrapped in alternating directions, and an oil- and weather-resistant synthetic rubber cover. A ply, or braid, of suitable material may be used over the inner tube and/or over the wire reinforcement to anchor the synthetic rubber to the wire.

Type AT has the same construction as Type A, but AT has a cover designed to assemble with fittings that do not require removal of the cover or any portion of it.

SAE 100R10 hose should be used with petroleum- and water-based hydraulic fluids within a temperature range from140° to 100° C.

Type A consists of an inner tube of oil-resistant synthetic rubber, four spiral plies of heavy wire wrapped in alternating directions, and an oil- and weather-resistant synthetic rubber cover. A ply, or braid, of suitable material may be used over the inner tube and/or over the wire reinforcement to anchor the synthetic rubber to the wire.

Type AT has the same construction as Type A, but AT's cover is designed to assemble with fittings that do not require removal of the cover or any portion of it.

HYDEAULLIC HOSE

SAE 100R11 hose should be used with petroleum- and water-based hydraulic fluids within a temperature range from 140° to 100° C. It consists of an inner tube of oil-resistant synthetic rubber, six spiral plies of heavy wire wrapped in alternating directions, and an oil- and weather-resistant synthetic rubber cover. A ply, or braid, of suitable material may be used over the inner tube and/or over the wire reinforcement to anchor the synthetic rubber to the wire.

SAE 100R12 hose should be used with petroleum- and water-based hydraulic fluids, within a temperature range from 140° to 121° C. It consists of an inner tube of oil-resistant synthetic rubber, four spiral plies of heavy wire wrapped in alternating directions, and an oil- and weather-resistant synthetic rubber cover. A ply, or braid, of suitable material may be used over the inner tube and/or over the wire reinforcement to anchor the synthetic rubber to the wire.

HYDEAULLIC HOSE

SAE 100R13 hose should be used with petroleum- and water-based hydraulic fluids, within a temperature range from 140° to 121° C. It is constructed with an inner tube of oil-resistant synthetic rubber, followed by multiple spiral plies of heavy wire wrapped in alternating directions, and concluding with an oil- and weather-resistant synthetic rubber cover. A ply, or braid, of suitable material may be used over the inner tube and/or over the wire reinforcement to anchor the synthetic rubber to the wire.

SAE 100R14 hose should be used with petroleum-, synthetic-, and water-based hydraulic fluids within a temperature range from 154° to 204° C.

Type A consists of an inner tube of polytetrafluorethylene (PTFE) reinforced with a single braid of type 303XX stainless steel.

Type B has the same construction as Type A, but B has the additional feature of an electrically-conductive inner surface to prevent buildup of an electrostatic charge.

HYDEAULLIC HOSE

SAE 100R15 hose should be used with petroleum-based hydraulic fluids within a temperature range from 140° to 121° C. It consists of an inner tube of oil-resistant synthetic rubber, multiple spiral plies of heavy wire wrapped in alternating directions, and an oil- and weather-resistant rubber cover. A ply, or braid, of suitable material may be used over or within the inner tube and/or over the wire reinforcement to anchor the synthetic rubber to the wire.

SAE 100R16 hose should be used with petroleum- and water-based hydraulic fluids, within a temperature range from140° to 100° C. It consists of an inner tube of oil-resistant synthetic rubber, steel wire reinforcement of one or two braids, and an oil-and weather-resistant synthetic rubber cover. A ply, or braid, of suitable material may be used over the inner tube and/or over the wire reinforcement to anchor the synthetic rubber to the wire.

HYDRAULIC FLUID Hydraulic fluids, also called hydraulic liquids, are the

medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water.Examples of equipment that might use hydraulic fluids include excavators and backhoes, hydraulic brakes, power steering systems, transmissions, garbage trucks, aircraft flight control systems, lifts, and industrial machinery.

Hydraulic systems like the ones mentioned above will work most efficiently if the hydraulic fluid used has low compressibility.

HYDRAULIC OIL FUNCTIONS AND PROPERTIES

Function & property

Medium for power transfer and control

1. Low compressibility (high bulk modulus)2. Fast air release3. Low foaming tendency4. Low volatility

Medium for heat transfer 5. Good thermal capacity and conductivity

Lubricant

Viscosity for film maintenanceLow temperature fluidityThermal and oxidative stabilityHydrolytic stability / water toleranceCleanliness and filterabilityDemulsibilityAntiwear characteristicsCorrosion control

HYDRAULIC OIL FUNCTIONS AND PROPERTIES

Pump efficiency

1. Proper viscosity to minimize internal leakage2. High viscosity index

Special function

Fire resistanceFriction modificationsRadiation resistance

Environmental impact

Low toxicity when new or decomposedBiodegradability

CHARACTERISTICS OF A GOOD HYDRAULIC FLUID

Viscosity Viscosity is a measure of a hydraulic fluid's resistance to flow. It is a

hydraulic fluid's most important characteristic and has a significant impact on the operation of the system.

When a hydraulic oil is too thin (low viscosity), it does not seal sufficiently. This leads to leakage and wear of parts. When a hydraulic oil is too thick (high viscosity), the fluid will be more difficult to pump through the system and may reduce operating efficiency.

All hydraulic fluids must be able to retain optimum viscosity during operation in cold or hot temperatures, in order to consistently and effectively transmit power. .

Compressibility Compressibility is a measure of the amount of volume reduction due to

pressure. Although hydraulic oils are basically incompressible, slight volume reductions can occur under certain pressure ranges.

Compressibility increases with pressure and temperature and has significant effects on high-pressure fluid systems. It causes servo failure, efficiency loss, and cavitation; therefore, it is important for a hydraulic oil to have low compressibility.

Wear Resistance

Wear resistance is a hydraulic fluid's ability to reduce the wear rate in frictional boundary contacts. Antiwear hydraulic fluids contain antiwear components that can form a protective film on metal surfaces to prevent abrasion, scuffing, and contact fatigue. Antiwear additives enhance lubricant performance and extend equipment life.

Oxidation Stability

Oxidation stability is a hydraulic oil's resistance to heat-induced degradation caused by a chemical reaction with oxygen. Hydraulic oils must contain additives that counteract the process of oxidation, improve the stability and extend the life of the fluid. Without these additives, the quality of the hydraulic oil will deteriorate quickly.

Thermal Stability

Thermal stability is the ability to resist breakdown at elevated temperatures. Antiwear additives naturally degrade over time and this process can be accelerated at higher temperatures. The result of poor thermal stability is the formation of sludge and varnish which can clog filters, minimize flow and increase downtime. In addition, as these antiwear agents decompose at high temperatures, acids are formed which attack bronze and yellow metals in piston pumps and other hydraulic system components. Hydraulic oils can be formulated with very high levels of thermal stability to minimize these issues and help extend the life of the hydraulic fluid and the components of the hydraulic system.

Filterability

Water can react with additives in hydraulic fluids forming oil insoluble material. These contaminants can precipitate from the lubricant and block filters, valves and other components resulting in decreased oil flow or the system going on bypass. Blockage can eventually result in unplanned downtime. Hydraulic fluids are designed to be filtered with modern filtration systems without fear of the additive being depleted or removed from the system. This enables systems to stay clean without sacrificing critical performance requirements such as antiwear, rust protection or foam inhibition.

Rust and Corrosion Protection

In many systems, water can enter as condensation or contamination, and mix with the hydraulic oil. Water can cause rusting of hydraulic components. In addition, water can react with some additives to form chemical species which can be aggressive to yellow metals. Hydraulic oil formulations contain rust and corrosion inhibitors which prevent the interaction of water or other chemical species from attacking metal surfaces.

Foam Resistance

Foam results from air or other gases becoming entrained in the hydraulic fluid. Air enters a hydraulic system through the reservoir or through air leaks within the system.

A hydraulic fluid under high pressure can contain a large volume of dissolved or dispersed air bubbles. When this fluid is depressurized, the air bubbles expand and produce foam. Because of its compressibility and poor lubricating properties, foam can seriously affect the operation and lubrication of machinery.

Proper foam inhibitors modify the surface tension on air bubbles so they more easily break up.

Demulsibility

Water that enters a hydraulic system can mix or emulsify with the hydraulic oil. If this 'wet' fluid is circulated through the system, it can promote rust and corrosion. Highly refined mineral oils permit water to separate or demulsify quickly. However, some of the additives used in hydraulic oils promote emulsion formation, preventing the water from separating and settling out of the fluid. Demulsifier additives are incorporated to promote water separation from hydraulic fluids.

Hydrolytic Stability

When hydraulic fluids come into contact with water, the water can interact with the additive system of the hydraulic oil resulting in the formation of acids. Hydraulic fluids that lack hydrolytic stability hydrolyze in the presence of water to form oil insoluble inorganic salts that can block filters and valves inhibiting oil flow. This can result in hydraulic system failure. Properly formulated hydraulic fluids are designed to contain additives that are resistant to interactions with water, helping to extend the life of the equipment.

Seal Compatibility Leaking hydraulic fluids can cause many issues from

simple housekeeping problems to more serious safety concerns and lubrication failures. Most hydraulics systems utilize rubber seals and other elastomers to minimize or prevent hydraulic oil leakage. Exposure of the elastomer to the lubricant under high temperature conditions can cause the rubber seals to harden, crack and eventually leak. On the other hand, hydraulic oil exposure can seals to swell excessively preventing hydraulic valves and pistons from moving freely. Hydraulic oils are tested against a variety of seal materials to ensure that the hydraulic fluid will be compatible with seals under various conditions.

BASIC HYDRAULIC CIRCUIT

BASIC HYDRAULIC CIRCUITControl of a Single Acting HydraulicCylinder

Two PositionThree WayManually ActuatedSpring Offset DCV

BASIC HYDRAULIC CIRCUITControl of a Double ActingHydraulic Cylinder

Three PositionFour WayManually ActuatedSpring Centered DCV

Regenerative Circuit

1) Pressurized fluid discharge returned to system

2)Speed up extending speed

3) Retraction bypass

A regeneration circuit can double the extension speed of a single-rod cylinder without using a larger pump. This means that regeneration circuits save money because a smaller pump, motor, and tank can produce the desired cycle time. It also means that the circuit costs less to operate over the life of the machine.

BASIC HYDRAULIC CIRCUITDrilling Machine Application

1) Spring centered position – Rapid spindle advance

2) Left envelope – Slow feed

3) Right envelope – Retracts piston

PUMP Unloading circuit

1) Unloading valveunloads the pumpat the ends ofextending andretracting strokes

2) As well as inspring centeredposition of DCV

BASIC HYDRAULIC CIRCUITDouble Pump Hydraulic System

1)Punch Press Initial LowPressure highflow rate req.

2)When punchingoperation begins,increasedpressure opensunloading valveto unload lowpressure pump.

Counterbalance Valve

To keep verticallymounted cylinder inupward position whilepump is idling.

Counterbalancevalve is set to openat slightly above thepressure required tohold the piston up.

BASIC HYDRAULIC CIRCUITHydraulic Cylinder SequenceCircuit

1)Left Env: Left Cylextends completelyand then Right Cylextend.

2)Right Env: Right Cylretracts fully andthen Left Cylretracts.

Cylinder Synchronizing Circuit

Pump pressure should overcome loadacting on both cylinders.P1Ap1- P2(Ap1-Ar1) = F1P2Ap2- P3(Ap2-Ar2) = F2

Fail Safe Circuit

Designed to prevent injury to operator ordamage to equipment.

Prevent Cylinder fromaccidentally falling on anOperator in the event of:

Hydraulic line ruptures Person inadvertently operatesmanual override on Pilotactuated DCV when pump notoperating

Two hand Safety Circuit

Designed to protectan operator frominjury.

For circuit tofunction, operatormust depress bothmanually actuatedvalves.

Any one buttonprevents operation.

BASIC HYDRAULIC CIRCUITHydraulic Motor Braking System

OPEN & CLOSE CIRCUIT As Open Loop the pumps have a Suction line connected to tank and an Outlet line connected to Directional Control Valves like most hydraulic circuits no matter the pump type. The Directional Control Valves determine actuator function and direction. They can be Fixed Volume, Pressure Compensated and/or Variable Volume.

As Closed Loop the flow lines are directly connected to an actuator (Commonly a Hydraulic Motor) and all oil leaving one pump flow port goes to the actuator and all oil from the actuator returns to the opposite pump flow port.

In closed loop system, one additional pump is used for making up the circuit fluid. And the direction of the direction of the movement of the actuator is controlled by the swash plate of the variable displacement pump.

The open loop hydraulic system has advantage of less heat generation and on the other hand the closed loop circuit is preferred for better (precise) response of the actuation.

CYLINDER CUSHIONING

Closed Circuit One-DirectionClosed Circuit thatof motor rotation. Motor speed varied bychanging pumpdisplacement.

Torque capacity of motoradjusted by pressuresetting of the relief valve

BASIC HYDRAULIC CIRCUITClosed Circuit Reversible DirectionHydrostatic Transmission

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