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CIRCUITS
PNEUMATIC LOGIC CIRCUITS
FLUIDICS
ELECTRICAL AND ELECTRONIC CONTROLS
TRANSFER DEVICES AND FEEDERS
ROBOTICS
ROBOTIC SENSORS
ROBOT END EFFECTORS
ROBOT PROGRAMMING
APPLICATIONS OF ROBOTS
ROBOTS USING REAL-TIME EMBEDDED SYSTEMS
INDEX
PREFACE
AUTOMATION
INTRODUCTION
DEFINITION OF AUTOMATION
Automation is the process in industry where various production operations are converted from a manual process, to an automatic or mechanized process. Manual, direct labor work will be progressively transformed into work, which will be cleaner, easier, safer and more rewarding for the worker, who through the process of automation will himself be trained for the more skilled performance required in the better jobs of the future.
MECHANIZATION VS AUTOMATION
Automation is a technology that deals with the application of mechatronics and computers for the production of goods and services. Automation creates jobs for skilled workers at the expense of unskilled and semi-skilled workers.
ADVANTAGES OF AUTOMATION
GOALS OF AUTOMATION
SOCIAL ISSUES OF AUTOMATION
Currently, for manufacturing companies, the goal of automation has shifted from increasing productivity and reducing costs to increasing quality and flexibility in the manufacturing process. Living standards rise with the increase in productivity, and automation is the sure method of increasing productivity.
LOW COST AUTOMATION
For uncomplicated situations, a simple LCA device can be constructed using any of the above systems with a rapid techno-economic assessment. However, in most practical applications, hybrid systems are used because they can make use of the advantages of different devices while minimizing individual disadvantages.
Issues in Low Cost Automation
TYPES OF AUTOMATION
Fixed Automation (Hard Automation)
Programmable Automation
Flexible Automation (Soft Automation)
With a flexible automation system, it is possible to quickly incorporate changes to the product (which can be redesigned in response to changing market conditions and consumer feedback) or to quickly introduce a new product line. Flexible automation allows the manufacturer to produce more products cheaply in combination than individually.
CURRENT EMPHASIS IN AUTOMATION
For example, Honda is widely credited with using flexible automation technology to introduce 113 changes to its motorcycle product line in the 1970s. Another major change in automation is the increased emphasis on flexibility and convertibility in the production process.
REASONS FOR AUTOMATION
Hazardous processes such as oil refining, industrial chemical production, and all forms of metalworking have always been early candidates for automation.
REASONS FOR NO AUTOMATION
ISSUES FOR AUTOMATION IN FACTORY OPERATIONS
STRATEGIES FOR AUTOMATION
EXERCISES
BASIC LAWS AND PRINCIPLES
FLUID PROPERTIES
Pressure
Atmospheric Pressure
Atmospheric pressure is defined as the pressure due to the weight of the atmosphere (air and water vapor) on the earth's surface. Mean atmospheric pressure at sea level is defined as 1.01325 bar, or 14,696 pounds per square inch absolute (PSIA).
Absolute Pressure
Atmospheric pressure is determined by a mercury column barometer, therefore it is sometimes called barometric pressure.
Gauge and Vacuum Pressure
Pascal’s Law
Flow and Flow Rate
Bernoulli’s Equation
Venturi Effect
There is a pressure drop at the taper, as indicated by the height of the column, and is due to energy conservation. The fluid experiences an increase in kinetic energy and a drop in pressure as it enters the constriction; this effect is called the Venturi effect, named after the Italian physicist Giovanni Battista Venturi.
Continuity Equation
Specific Weight, Density, and Specific Gravity
Density is defined as the ratio of an object's mass to its volume. The ratio of the density (or specific gravity) of a substance to the density (or specific gravity) of a standard liquid is called specific gravity or relative density.
Compressibility and Bulk Modulus
On the other hand, the volume of the gases can be easily changed by applying an external pressure to the gas. An internal combustion engine is a good example of the ease with which gases can be compressed.
Viscosity and Viscosity Index
The hydraulic braking systems used in most cars operate on the principle that there is essentially no change in the volume of brake fluid when pressure is applied to this fluid. Where B is called the bulk modulus of elasticity and is defined as the ratio of change in pressure to volumetric stress (change in volume/original volume) across a fluid element.
Gas Laws
Any two of the three gas laws of Boyle, Charles or Gay-Lussac can be combined, hence the name, combined gas law. This relationship can be used to predict pressure, volume, and temperature relationships where any five of the six variables are known.
Moisture in the Air
The dew point is the temperature at which water vapor begins to condense from the air. The pressure dew point is the temperature value at which moisture present in the air begins to condense at pressures higher than atmospheric pressure.
Energy, Work, and Power
Atmospheric dew point is the value of the temperature at which moisture present in the air begins to condense at atmospheric pressure, i.e. at 1.01325 bar. Energy is the ability to do work and is expressed in foot pounds (ft lb) or Newton meters (Nm).
BASIC PNEUMATIC AND HYDRAULIC SYSTEMS
INTRODUCTION TO FLUID POWER
Fluid power encompasses most applications that use fluids or gases to transmit power in the form of mechanical work, pressure, and/or volume in a system. Fluid power is used in the steering, braking system and automatic transmissions of cars and trucks.
BASIC ELEMENTS OF FLUID POWER SYSTEM
ADVANTAGES AND DISADVANTAGES OF FLUID POWER
Motion can be transferred without the backlash inherent in using solid machine parts. These forces can be transported up and down or around corners with a small loss of efficiency and without complicated mechanisms.
APPLICATIONS OF FLUID POWER
Low Speed Torque: Unlike electric motors, air or hydraulic motors can produce large amounts of torque (turning force) at low speeds. Fluid actuators, hydraulic or pneumatic, are well suited for walking robots because they are powerful, low-speed actuators.
Mobile
Safety in Hazardous Environments: Liquid power can be used in mines, chemical plants, near explosives and in paint applications because it is essentially non-sparking and can tolerate high temperatures. The main disadvantage of a liquid system is the preservation of precision parts when they are exposed to bad climates and dirty atmospheres.
Industrial
Low running costs: Fluid power systems are economical to operate their high efficiency with minimal friction loss keeps the cost of a power transmission to a minimum. Fluid power is used to provide power transmission and motion control for industrial machinery.
Aerospace
PNEUMATICS VS. HYDRAULICS
ADVANTAGES AND DISADVANTAGES OF PNEUMATICS
Compressed gas can be stored, enabling the use of machines when electrical power is lost.
ADVANTAGES AND DISADVANTAGES OF HYDRAULICS
APPLICATIONS OF PNEUMATICS
APPLICATIONS OF HYDRAULICS
BASIC PNEUMATIC SYSTEM
The compressor turns off automatically when the pressure is about to exceed the high limit, and it also turns on automatically when the pressure is about to drop below the low limit. Safety valve: The function of the safety valve is to release additional pressure if the pressure inside the receiver tends to exceed the safe pressure limit of the receiver.
BASIC HYDRAULIC SYSTEM
Directional control valve: Directional control valves are devices used to change the direction of fluid flow within a pneumatic/hydraulic circuit. Strainers, filters and magnetic plugs are used to remove foreign particles from the hydraulic fluid and are effective protection against contamination.
HYDRAULIC SYSTEM DESIGN
The oil level must be as high as possible above the opening to the suction line of the pump. The vent allows air to leave or enter the space above the oil as the oil level rises or falls.
FLUIDS USED IN HYDRAULICS
Some components must be mounted in a certain position in relation to other components or pipes. The correct working pressure is the lowest pressure that will allow adequate performance of the system function while remaining below the maximum rating of the components and machine.
Petroleum-Based Fluids
Synthetic Fire-Resistant Fluids
Water-Based Fire-Resistant Fluids
What are the properties of pneumatic power that make it suitable for engineering applications.
PUMPS AND COMPRESSORS
PUMPS VS. COMPRESSORS
POSITIVE DISPLACEMENT VS. NON POSITIVE DISPLACEMENT DEVICES
Devices without positive displacement are those in which the fluid is compressed by the dynamic action of rotating vanes or rotors that impart velocity and pressure to the fluids.
CLASSIFICATION OF HYDRAULIC PUMPS
POSITIVE DISPLACEMENT PUMPS
ROTARY PUMPS
Gear Pump
They are one of the most common types of pumps for hydraulic fluid power applications. Gear pumps are fixed displacement, meaning they pump a constant amount of fluid for each revolution.
External Gear Pump
Refer to Figure 4.3 (b).) As the gears emerge from the mesh, they create expanding volume on the inlet side of the pump. Finally, the meshing of the gears forces oil through the outlet port under pressure as shown in Figure 4.3 (c).
Internal Gear Pump
An internal gear is engaged with the drive shaft and has one less tooth than an external gear. During rotation, each tooth of the internal gear is in constant contact with the external gear.
Lobe Pump
As the rotors begin to rotate, an expanding cavity is formed by the rotation of the lobes, creating a vacuum at the inlet port, which draws fluid into the pump chamber. Fluid moves around the inside of the casing in the pockets between the lobes and the casing.
Vane Pump
Complex housing and many parts Not suitable for high pressures Not suitable for high viscosity Not good with abrasives.
Peristaltic Pump
The flow rate of the pump is directly related to the diameter of the pipe and the rotational speed of the drive. Some common applications include pumping aggressive chemicals, high solids slurries and other materials where isolation of the product from the environment and the environment from the product is critical.
Screw Pump
Twin-Screw Pumps
Multi-Screw Pumps
In multi-screw pumps, the fluid is transferred under the action of a number of screws attached together in a casing provided with channels to fit the screws. These pumps are used in the chemical process industry and in the oil industry for applications on oil rigs.
Piston Pumps
Each piston interfaces with the inlet and outlet ports via a special valve arrangement so that as it moves out of its cylinder, it draws in fluid and as it moves back, it expels the fluid.
Radial Piston Pump
Swash Plate Pump
The pistons draw fluid in during half a revolution and expel fluid during the other half. The greater the swashplate angle relative to the cylinder centerline, the longer the stroke of the pistons and the more fluid they transfer.
Wobble Plate Pump
Bent Axis Pump
The cylinder block is mounted on a shaft and this shaft is connected to the drive shaft with a universal joint. Due to the alternating action of the pistons, the liquid is forced through the inlet port with atmospheric pressure and discharged from the outlet port.
Flexible Impeller Pump
This linkage ensures that the drive shaft and cylinder block are properly aligned and rotate together. When the drive shaft rotates, the pistons are forced in and out of their bores because the distance between the cylinder block and the shaft flange changes.
Benefits of Impeller Pumps
RECIPROCATING PUMPS
Types of Reciprocating Pumps
Piston Pump/Plunger Pump
Diaphragm Pump
These pumps are suitable for abrasive materials such as acids, chemicals, concrete, coolants, flammable or corrosive materials and waste water. These pumps are used in a variety of industries such as aerospace or defense, agriculture or horticulture, automotive, brewery or distillery, construction, cryogenic, dairy or flood control applications, medical applications.
METERING PUMP
DYNAMIC/NON POSITIVE DISPLACEMENT PUMPS
CENTRIFUGAL PUMPS
Mixed flow: a centrifugal pump in which the pressure is developed on the liquid partly by means of centrifugal force and partly by the lifting of the wheels of the impeller. Axial flow: a centrifugal pump in which the pressure is developed by the driving or lifting action of the wheels of the impeller on the liquid.
PUMP SELECTION PARAMETERS
Fluid Handling Suitable for a wide range of clean, clear, non-abrasive fluids to fluids with an abrasive solids content.
AIR COMPRESSORS
Used in the foundry to clean large castings and to remove weld deposits, rust and paint in other industries. Grinding, wire brushing, polishing, sanding, shot blasting and polishing are efficiently performed with compressed air in the automotive, aircraft, railcar, locomotive, ship shops, shipbuilding, other heavy machinery and other industries.
TYPES OF AIR COMPRESSORS
POSITIVE DISPLACEMENT COMPRESSORS
ROTARY COMPRESSORS
Screw Compressor
The heat of compression is dissipated outside the compressor, limiting it to single-stage operation. In the oil-flooded screw compressor, the lubricant is injected into the air, which is trapped in the stator.
Lobe Compressor
In the dry screw type, the rotors run inside a stator without a lubricant (or coolant). Advantages of the rotary screw compressor include smooth pulse-free air output in a compact size with high output volume for long life.
Vane Compressor
RECIPROCATING COMPRESSORS
During the upward stroke, the piston compresses the air and forces it through a discharge control valve and out of the compressor. The reciprocating compressor is considered single-acting when compression is achieved using only one side of the piston.
PISTON COMPRESSORS
The reciprocating air compressor accomplishes this by using a piston inside a cylinder as the compressive and displaceable element. As the piston enters the downstroke, air is drawn from the atmosphere into the cylinder through an air intake valve.
Single-Stage Piston Compressor
The upward movement of the piston compresses the air in the cylinder, causing the intake valve pressure to equalize and the intake valve to reset. When the discharge valve is open, the air compressed in the cylinder is released until the piston completes its stroke.
Two-Stage Piston Compressor
When the pressure drops below the pressure on the other side of the intake valve, the valve opens and lets air in until the pressure is equal across the intake valve. The piston continues to compress air during the rest of the upstroke until the cylinder pressure is great enough to open the discharge valve against the valve spring pressure.
DIAPHRAGM COMPRESSOR
DYNAMIC COMPRESSORS
Centrifugal/Axial Compressors
To do this efficiently, centrifugal compressors rotate at higher speeds than the other types of compressors. These types of compressors are also designed for higher capacity because the flow through the compressor is continuous.
Axial Flow Compressor
Compared to other types of compressors, axial compressors are mainly used for applications where the required head is low. The operation of the axial flow compressor is a function of the rotational speed of the blades and the turning of the flow in the rotor.
SPECIFICATIONS OF COMPRESSORS
The stationary blades (stator) are used to spread the flow and convert the speed that is increased in the rotor to a pressure increase. Sketch constructional details of a variable displacement axial piston pump, name its components and explain how it works.
FLUID ACCESSORIES
AIR RECEIVER
Wet Air Receivers: Wet receivers provide additional storage capacity and reduce moisture. The large surface area of the air receiver acts
As moisture is reduced at this point in the system, the load on the filters and dryers will be reduced.
Dry Air Receivers: When sudden large air demands occur, dry air receivers should have adequate capacity to minimize a drop in system air
AFTERCOOLER
In some systems, aftercoolers are an integral part of the compressor package, while in other systems the aftercooler is a separate piece of equipment. The aftercooler should be located as close as possible to the discharge of the compressor.
Types of Aftercoolers
Much of the remaining 20% moisture is removed by an air dryer or series of air dryers. Typically, the compressed air flows through the tubes in one direction while water on the shell side flows in the opposite direction.
AIR DRYER
Types of Compressed Air Dryers
The compressed air, now free of liquid moisture, is reheated in the air-to-air precooler/reheater and discharged to the compressed air system. Absorption dryers use chemical granules called desiccant to absorb water vapor from compressed air (see Figure 5.3).
AIR FILTER
It must be installed upstream of all work equipment and in such a way that it cannot be overlooked to avoid damage to these equipment. To properly size a filter for a particular application, the maximum allowable pressure drop that can be caused by the filter must be determined.
Construction and Working of Pneumatic Filter
Clean, dry air protects the air system, reduces maintenance costs and increases the yield of the end product.
Types of Air Filters
PRESSURE REGULATOR
If the chamber pressure is already high, the incoming air must exert more and more pressure on the stem and diaphragm, against the force of the spring. On the other hand, if the pressure in the chamber is less than the force of the spring, air from an inlet port enters freely and quickly without any resistance and maintains the required pressure at which the spring is set.
AIR LUBRICATOR
It helps the system operate more economically by minimizing the amount of pressurized air that is wasted. Extends component life because operating at higher than recommended pressures increases wear rate and reduces equipment life.
AIR SERVICE UNIT (F.R.L.)
PIPELINE LAYOUT
Condensate Control
Another method to control the condensation is to take all the branch connections from the top of the airline. This eliminates condensation from entering the branch connection and allows the condensate to continue to the low points in the system.
Pressure Drop
Piping Material
It is always best to oversize the compressed air piping system you choose to install. Corrosion-resistant piping must be used with any compressed air piping system using oil-free compressors.
SEALS
Plastic pipes can be used on compressed air systems; caution is advised, however, as many plastic materials are not compatible with all compressor lubricants. Ultraviolet light (sunlight) can also shorten the useful life of some plastic materials.
Classification of Seals
-Resistant piping must be used with any compressed air piping system using oil-free compressors. Seal materials are generally made of rubber or metal, and in some cases, leather or felt.
Pneumatic Seals
HYDRAULIC FLUIDS
Lubrication: Hydraulic fluids must provide the lubrication properties and qualities necessary to protect all hydraulic system components against friction and wear, rust, oxidation, corrosion and demulsibility. In these applications, hydraulic fluids must provide the seal between the low-pressure and high-pressure sides of the valve ports.
Properties of Hydraulic Fluids
Prevent Rust: Moisture and oxygen cause iron parts in the system to rust, which can lead to abrasive wear on system components and also act as a catalyst to increase the oxidation rate of the fluid. Excessive water in the oil promotes the accumulation of contaminants, causing sticky valves and accelerated wear.
Types of Hydraulic Fluids
These liquids have low viscosities, excellent fire resistance and good cooling capacity due to the large amount of water. Synthetic Fire Resistant Fluids: These fluids are usually a mixture consisting of phosphate esters, chlorinated hydrocarbons and hydrocarbon based fluids.
HYDRAULIC RESERVOIR
Additives should be used to improve their inherently poor lubricity and to protect against rust. These fluids do not contain water or volatile substances and provide satisfactory operation at high temperatures without loss of essential elements (unlike water-based fluids).
HYDRAULIC FILTER
Hydraulic tanks are usually rectangular, cylindrical, T-shaped or L-shaped and are made of steel, stainless steel, aluminum or plastic. Hydraulic reservoirs vary in capacity, but must be large enough to accommodate thermal expansion of fluids and changes in fluid level due to normal system operation.
Construction and Working of Hydraulic Filter
Types of Filters
Filter Location
Filtering Material and Elements
PRESSURE GAUGES AND VOLUME METERS
HYDRAULIC ACCUMULATOR
Active absorbent materials, such as charcoal and full earth (a very fine-grained clay-like material used in cleaning mineral or vegetable-based oils), are not recommended for plumbing systems. Because of their ability to store excess energy and release it when needed, accumulators are useful tools in developing efficient hydraulic systems.
Applications/Functions of an Accumulator
An accumulator is essentially a pressure storage reservoir in which a non-compressible hydraulic fluid is retained under pressure from an external source. Accumulators are used with hydraulic systems on large hydraulic presses, farm machinery, diesel engine starters, power outages on aircraft, elevators, etc.
Types of Accumulators
The pressure in the fluid depends on the weight on the piston and the size of the piston and can be changed by adding or removing weight from the piston. As the volume of the compressed gas changes the pressure of the gas, and the pressure on the liquid changes inversely.
INTENSIFIER
Cylinder speed: If rapid cylinder action is required, the hydraulic cylinder should be sized so that the reaction force (force required to do work)
LINES
Flexible hose must be installed so that it will be subjected to a minimum of bending during operation. All lines must be installed in such a way that they can be removed without disassembling a circuit's components or without bending or springing them to a bad angle.
FITTINGS AND CONNECTORS
Hose Connections: A hydraulic hose consists of an inner tube through which the fluid is conveyed and comes into direct contact with the hydraulic fluid. The hydraulic hose is an important element in the system that must be checked for reliability and durability during the manufacturing process.
HYDRAULIC SEALS
The hydraulic hoses can be made using a variety of materials, depending on the factors of oil compatibility, wear resistance, etc. Sealing keeps the hydraulic oil in the passage to maintain pressure and prevent foreign materials from entering the hydraulic passages.
CYLINDERS AND MOTORS
Fluid motors are used to transmit power in various pneumatic and hydraulic devices in industry. On the other hand, with variable displacement engines, the relative position of internal and external parts can be changed to obtain different combinations of rotational frequencies.
CYLINDERS
When pressure is applied to a port, it causes that side of the cylinder to fill with fluid. If the fluid pressure and the surface area of the cylinder are greater than the load that is attached, then the load will move.
CLASSIFICATION OF CYLINDERS
CLASSIFICATION OF CYLINDERS ON THE BASIS OF CONSTRUCTION
SINGLE-ACTING CYLINDER
In mobile equipment, flow to and from a single-acting cylinder is controlled by a reversing valve of a single-acting type.
DOUBLE-ACTING CYLINDER
Construction of a Double-Acting Cylinder
Other points where seals are used are at the end cap and joints and between the piston and cylinder. Mounting features are often incorporated into the end caps, including flanges for stationary mounting or clevises for swing brackets.
TYPES OF SINGLE-ACTING CYLINDERS
The barrel is usually a seamless steel tube or cast, and the interior is finished very true and smooth. Seals and wipers are installed in the rod end cap to keep the rod clean and prevent external leakage around the rod.
Ram Type Cylinder
Telescoping Cylinder
Spring Return Cylinder
TYPES OF DOUBLE-ACTING CYLINDERS
Double Rod/Through Rod Cylinder
Tandem Cylinder
OTHER TYPES OF CYLINDERS
Tie-Rod Cylinder
One-Piece Cylinder
Threaded Head Cylinder
Diaphragm Cylinder
Rotating Cylinder
Non-Rotating Cylinder
Duplex Cylinder
CLASSIFICATION OF CYLINDERS ON THE BASIS OF WORKING MEDIUM
HYDRAULIC CYLINDERS
Single-acting hydraulic cylinders require fewer valves and piping than double-acting cylinders. A typical hydraulic double-acting cylinder, complete with all parts, is shown in Figure 6.17, and the parts list is given in Table 6.1.
PNEUMATIC CYLINDERS
APPLICATIONS OF CYLINDERS
CYLINDER CUSHIONING
Working of Cushions
To overcome this problem, a check valve gallery is sometimes provided below the cushion chamber to start the process without spending much time. Ideal damping means that there is no end to impact ie. the piston's direction of motion is the same throughout the shock absorption sequence and that its velocity is exactly zero when it reaches the end of its travel.
CYLINDER MOUNTINGS
Now when the process is complete and the pad nose fully enters the pad chamber, then it will take time to start the forward stroke because the nose area is large, while the fluid inlet is deliberately kept small. The manner in which a cylinder is assembled is critical to its performance and longevity.
Extended Tie-Rods Mounting
Improper installation or using an inappropriate mounting style can result in distortion, which causes damaging lateral loading and bending. NFPA (National Fluid Power Association) recommended mounting styles for connecting rod mounted cylinders are shown in Figure 6.22.
Flange-Mounted Cylinders
Mounting styles recommended by the NFPA (National Fluid Power Association) for flange-mounted cylinders are shown in Figure 6.24.
Side or Lug Mounted Cylinders
NFPA (National Fluid Power Association) recommended mounting styles for cylinders using plugs are shown in Figure 6.26.
Pivot-Mounted Cylinders
Trunnion-Mounted Cylinders
CYLINDER SIZING
Area of a Cylinder
When fluid at the same pressure enters both the inlet and outlet ports, the force acting on the "rodless" side of the piston is greater because the area is greater in that case. Therefore, from the above expression, it is clear that the force F1 on the "rodless" side of the piston is greater than the force F2 on the "rod" side of the piston.
CYLINDER SPECIFICATION
P1 and P2 are the pressures acting on the two sides of the piston provided that P1. Let us assume that A1 and F1 are the area and force acting on the piston on the "rodless" side respectively and similarly A2 and F2 are the area and force acting on the piston rod side.
INTRODUCTION TO MOTORS
The flow of fluid to the motor is controlled by a flow control valve, a two-way directional control valve, or by starting and stopping the power supply. The flow to the motor is usually controlled by either a four-way directional control valve or a variable displacement pump.
MOTOR RATINGS
The speed of the motor can be controlled by varying the speed of the fluid flow to it. In most fluid power systems, the motor must provide motive power in both directions.
HYDRAULIC AND PNEUMATIC MOTORS
Typically, a pump is connected via a carrier line to a motor, which then draws fluid from a reservoir and forces it into the motor. The fluid forces the moving components of the motor into motion, which in turn rotates the attached shaft.
Advantages of Hydraulic Motors
In industrial hydraulic circuits, pumps and motors are usually combined with appropriate valves and piping to form a hydraulic power transmission. Unlike electric motors, many air motors can operate without the need for auxiliary speed reducers.
SYMBOL OF MOTORS
They generally have a higher power density, so a smaller air motor can deliver the same power as its electric counterpart. Air motor speed can be regulated by simple flow control valves instead of expensive and complicated electronic speed control.
CLASSIFICATION OF FLUID MOTORS
Fluid motors are usually classified according to the type of internal element that is directly actuated by flow.
GEAR MOTORS
VANE MOTORS
These have the ability to operate at high speeds; however, they are ineffective at low speeds. Hydraulic vane motors are the most popular general purpose motor, but they are limited by their tolerance of high pressure systems and the higher percentage of slippage or internal leakage relative to the lower total fluid flow at low speeds.
PISTON MOTORS
Swash Plate In-Line-Axis Piston-Type Motors
Swash Plate Bent Axis Piston Type Motors
This design of piston motor is very heavy and bulky, especially the variable displacement motor. Although some piston type motors are controlled by directional control valves, they are often used in combination with variable displacement pumps.
Radial-Piston Motors
This pump-motor combination (hydraulic transmission) is used to provide a power transfer between a moving element, such as an electric motor, and a driven element. Hydraulic transmissions can be used for applications such as a speed reducer, a variable speed drive, a constant speed or constant torque drive, and a torque converter.
APPLICATION OF MOTORS
With the help of a neat sketch, show the different parts of hydraulic and pneumatic double-acting cylinders. With the help of a neat sketch, explain the construction and operation of gear and fan motors.
CONTROL VALVES
CLASSIFICATION OF VALVES
Directional control valve Flow control valve Pressure control valve Check valve Directional control valves are the most important among all other valves because of their frequent use in a fluid power system. Flow control valves are those in which the flow of liquid is varied according to requirements.
DIRECTION CONTROL VALVES
As the name suggests, they are used to direct the fluid flow in a desired direction. All other valves where the free flow of liquid is only allowed in one direction fall under the category of non-return valves, e.g. non-return valve, quick exhaust valve, double pressure valve, non-return valve, etc.
SYMBOL AND DESIGNATION OF DIRECTION CONTROL (DC) VALVE
They are ON, OFF or Neutral (1, 2 or 0) and each position of the valve is shown by a separate box. In the valve symbol shown in Figure 7.5, right side position is the normal position of the valve.
CLASSIFICATION OF DC VALVES
CLASSIFICATION OF DC VALVES ON THE BASIS OF METHODS OF VALVE ACTUATION
Pressure is applied to the handle and the position of the valve changes. When the actuating force is removed, the spring returns the valve to its original position.
SYMBOLS FOR VALVE ACTUATORS
For example, a 3/2 pilot operated DC valve (pneumatic or hydraulic), used to drive the main 5/2 DC valve, is itself controlled by a solenoid valve. The symbols for valve actuators are drawn along the end of the valve boxes.
CLASSIFICATION OF DC VALVES ON THE BASIS OF CONSTRUCTION
All ports are blocked in the intermediate position when the valve rotates, as shown in Figure 7.13 (b). When the coil is moved to either side, the current path is closed, as shown in Figure 7.15 (b).
2/2 DC VALVES
2/2 Spool Type DC Valve
2/2 Seat Type DC Valve
3/2 DC VALVES
3/2 Spool Type DC Valve
3/2 Seat Type DC Valve
4/2 DC VALVES
4/2 Spool Type DC Valve
4/2 Seat Type DC Valve
CENTER CONDITIONS IN 4 WAY DC VALVES
Closed center mode: In closed center mode, all ports are blocked as shown in Figure 7.28. Tandem center mode: In tandem center mode, the pressure port is connected to the tank port and both actuator ports are blocked as shown in Figure 7.29.
CHECK VALVE
Pressurized fluid exiting the cylinder must pass through control valves and variable restrictors. Therefore, the cylinder speed can be reduced by using flow control valves.
PILOT OPERATED CHECK VALVE
PRESSURE CONTROL VALVES
PRESSURE RELIEF VALVE
