Chapter 1 Intoduction to Pneumatic PREPARED BY MOHD

Chapter 1 Intoduction to Pneumatic PREPARED BY MOHD SHAHRIL SHARIFF

Introduction of Transmission Power System Three basic methods of transmitting power 1. Mechanical Power System 2. Electrical 3. Pneumatic Fluid Power 4. Hydraulic In practice, most application actually use the combination of the three methods to achieve the most efficient overall system.

Introduction of Transmission Power System (cont. ) Comparison of Power Systems

Introduction of Transmission Power System (cont. ) Fluid power is the method of using pressurized fluid to transmit energy. Liquid or Gas is referred to as a fluid. Accordingly, there are two branches of fluid power; Pneumatics, and Hydraulics. Hydraulic systems use liquid to transfer force from one point to another. Pneumatic systems use air to transfer force from one point to another. Air is

Introduction of Transmission Power System (cont. ) Air is Compressible: (This describes whether it is possible to force an object into a smaller space than it normally occupies. For example, a sponge is compressible because it can be squeezed into a smaller size). liquid is Incompressible: (The opposite to compressible. When a “squeezing” force is applied to an object, it does not change to a smaller size. Liquid, for example hydraulic fluid, possesses this physical property).

Definitions & Principle Definition Greek pneuma = breath (bernafas) while the "matic" refers to the ‘power’. The term pneumatics describes the use of compressed air in drive and control engineering. The introduction of pneumatics into mechanisation and automation began in the middle of the 20 th century.

Definition & Principle (cont. ) PNEUMATICS is application of compressed air (pressurized air) to power machine or control or regulate machines may be defined as branch of engineering science which deals with the study of the behavior and application of compressed air can also be defined as the branch of fluid power technology that deals with generation, transmission and control of power using pressurized air Gas in a pneumatic system behaves like a spring since it is compressible.

Definition & Principle (cont. ) For example, in tires and air-cushioned springs, compressed air acts as a cushion to absorb shock. Air brakes on locomotives and large trucks contribute greatly to the safety of railroad and truck transportation. Pneumatic principle

Application Areas of use Nowadays, compressed air can be found in almost all field of engineering, e. g. : - Industry Rail transport Motor vehicles Shipping Construction - Trade Air transport Mining Medicine Defence

Application Areas (cont. ) Application Area Generation of linear motion Example clamping, feeding, lifting and lowering, opening & closing, pneumatic press, transfer table, tool loading, industrial robot, etc Generation of rotary motion screw drivers, grinders, tread cutters, drill, etc sequence control, monitoring, locking, etc workshop air, paint spraying, etc Applications in control Others

Characteristics of Air A characteristic of air is its minimal cohesion forces, i. e. the forces between the air molecules are to be disregarded for operating condition usual in pneumatic. In common with all gases, air has no particular shape. Air is a mixture of different gases (78%, 21% oxygen, carbon dioxide, argon, hydrogen, neon, helium, krypton, xenon and water vapour) . For practical application within normal temperature and pressure ranges, air can be considered as an ideal gas, and the equation of state for gases can be applied

Compressed Air Fundamental Compressed Air (pressurized air) Compressed atmospheric air which stores energy in its compressed state (usually greater than that of the atmosphere) and has the potential to perform work. Among the simplest ways that air can be taken from the atmosphere and compressed within a smaller volume is through the use of a hand pump. To see how a hand pump works, look no further than a simple bicycle pump, which takes air and pumps it into a bike tire when a person repeatedly pushes a hand or foot pedal. When the pedal is compressed, air enters the pump through an intake and is “pushed” into the bike tire via a plunger within the pump casing. Once the air has entered the tire, it officially has become compressed air, and the more air that enters the tire results in higher air pressure within the volume of the tire.

Compressed Air Fundamental (cont. ) Gauge pressure Pressure measuring devices normally measure the difference between applied pressure and atmospheric pressure and thus indicate gauge pressure (or vacuum pressure in the case of a vacuum gauge). The equivalent absolute pressure is determined by relating the gauge pressure to zero pressure as a datum. In the case of positive pressure above atmosphere, absolute pressure is the sum of the gauge and the atmospheric pressure (normally assumed to be 1 bar). Since pneumatics are mainly concerned with gauge pressure less than 10 bar, the difference between absolute and gauge pressure can be significant.

Compressed Air Fundamental (cont. ) Pressure measurement Instruments used to measure pressure are called pressure gauges or vacuum gauges. Standard model for pressure gauge: 1. Bourdon tube pressure gauge 2. Diaphragm pressure gauge 3. Piston spring pressure gauge

Compressed Air Fundamental (cont. ) Perfect Gas principle (ideal gases) Boyle's law states that the volume (V) of a gas, at constant temperature varies inversely with the pressure (P). = constant Charles's law states that the volume of a gas, at constant pressure, varies directly with the absolute temperature (T). = constant Amonton's law states that the pressure of a gas, at constant volume, varies directly with the absolute temperature. = constant

Compressed Air Fundamental (cont. ) Compressed air in motion (a) Law of Conservation of mass (continuity equation) Matter cannot be created or destroyed - (it is simply changed in to a different form of matter). ρ1 v 1 A 1 = ρ2 v 2 A 2 = constant =mass flow rate (steady state) Law of Bernoulli’s equation Bernoulli’s states: “if a liquid of specific gravity flows horizontally through a tube with varying diameters, the total energy at point 1 and point 2 is the same” P 1 + 1/2ρv 1 + z 1 = P 2 + 1/2ρv 2 + z 2

Compressed Air Fundamental (cont. ) (b) Type of flow 1. Laminar flow 2. Turbulent flow Laminar flow, occurs when a fluid flows in parallel layers, with no disruption between the layers. In laminar flow the motion of the particles of fluid is very orderly with all particles moving in straight lines parallel to the pipe walls. Turbulent flow is the opposite of laminar flow which occurs at higher velocities where small packets of fluid particles form leading to lateral mixing. Example : Smoke rising from a cigarette. For the first few centimetres, the flow remains laminar, and then becomes unstable and turbulent as the rising hot air accelerates upwards.

Compressed Air Fundamental (cont. ) (c) Pressure loss / Pressure drop is a term used to describe the decrease in pressure from one point in a pipe or tube to another point downstream. Pressure drop is the result of frictional forces on the fluid as it flows through the tube. The main factors impacting resistance to fluid (or air) flow: 1. Flow velocity through the pipe 2. Fluid viscosity 3. Surface roughness 4. Type of flow (laminar / turbulent flow)

Choice of Working Medium and System • When the system requirement is high speed, medium pressure (usually 6 to 8 bar) and less accuracy of position, then pneumatic system is preferred. • If the system requirement is high pressure and high precision, a fluid system with oil is good. • When the power requirement is high like in forging presses, sheet metal press, it is impossible to use air system. Oil hydraulics is the only choice • Air is used where quick response of actuator is required.

Choice of Working Medium and System (cont. ) • If temperature variation range in the system is large, then the use of air system may run into condensation problems and oil is preferred. • If the application requires only a medium pressure and high positional accuracy is required then hydro –pneumatic system is preferred • Air is non-explosive, it is preferred where fire/electric hazard are expected. Oil systems are more prone to fire and electrical hazards and are not recommended in such applications. • Because air contains oxygen (about 21%) and is not sufficient alone to provide adequate lubrication of moving parts and seals, oil is usually introduced into the air stream near the actuator to provide this lubrication preventing excessive wear and oxidation.

Advantages of Pneumatics • Air is available practically everywhere in unlimited quantities. • Air can be easily transport in pipelines, even over large distance. • Compressed air can be stored in a reservoir and removed as required. In addition, the reservoir can be transportable. • Compressed air is relatively insensitivity to temperature fluctuations. This ensure reliable operation, even under extreme conditions • Compressed air offers no risk of explosion or fire • Unlubricated exhausted air is clean. Any unlubricated air which escapes through leaking pipes does not cause contamination • Simple construction and relatively inexpensive. • Very fast working medium and high working speed.

Disadvantages of Pneumatics System • Suitable only for low pressure and hence low force applications • Compressed air actuators are economical up to 50 k. N only. • Generation of the compressed air is expensive compared to electricity • Exhaust air noise is unpleasant and silence has to be used. • Rigidity of the system is poor • Air cannot seal the fine gaps between the moving parts unlike hydraulic system • Less precise. It is not possible to achieve uniform speed due to compressibility of air • Pneumatic systems is vulnerable to dirt and contamination

Comparison Between Pneumatics & Hydraulics System Hydraulic It employs a pressurised liquid as fluid Pneumatic It employs a compressed gas usually air as a fluid Oil hydraulics system operates at pressure up to Pneumatics system usually operates at 5 to 700 bar 10 bar Generally designed for closed system Pneumatic systems are usually designed as open system System get slow down of leakage occurs Leakage does not affect the system much more Valve operation are difficult Easy to operate the valves Heavier in weight Light in weight Pump are used to provide pressurised liquids Compressors are used to provide compressed gas System is unsafe to fire hazards System is free from fire hazards Automatic lubrication is provided Special arrangements for lubrication needed

Pneumatics Component Classification Pneumatic circuit elements are classed into FIVE primary groups. ELEMENT Example 1. AIR SUPPLY AND CONDITIONING ELEMENTS Compressor, Receiver, Pressure regulator, Filter, Dryer, Lubricator 2. INPUT ELEMENTS (electrical or pneumatic) Push-button valve, Roller lever valves, Proximity switch 3. PROCESSING ELEMENTS Logic valves (And / Or, etc), Time delay valves, Pressure control valves, Sequencer 4. CONTROL ELEMENTS Directional control valves, throttle/choke valves 5. ACTUATING DEVICES/ POWER ELEMENT Cylinders, Motors, Semi-rotary actuators

Pneumatics Component Classifications (cont. ) Power element Control Element Processing Element Input Element Supply Element

Basic Components of Pneumatic System AIR SUPPLY AND CONDITIONING ELEMENTS Diagram of structural block Air Compressor Air Receiver Dryer Service Unit Control Valve Actuator

A. Air Compressor (generation of compressed air) A air compressor converts the mechanical energy of an electric or combustion motor into the potential energy of compressed air compressors can be split into positive displacement devices (intake air is compressed into decreasing volume to obtain the output pressure) and dynamic devices (intake air is accelerated by turbine and the kinetic energy of the air is converted to pressure). The vast majority of air compressors are of the positive displacement type. Pressure in the receiver is generally higher than that required at the operating position, with local pressure regulation being used.

A. Air Compressor (generation of compressed air) Piston type of compressors are used commonly in Industries.

1. Piston type compressor (single-stage compressor) Air taken in at atmospheric pressure is compressed to the required pressure in a single stroke. Downward movement of the piston increase volume to create a lower pressure than that of the atmosphere, causing air to enter the cylinder through the inlet valve. At the end of the stroke, the piston move upwards, the inlet valve closes as air is compressed, forcing the outlet valve to open discharging air into a receiver tank. This type of compressor is generally used in systems requiring air in the 37 bar ranges.

1. Piston type compressor (multi-stage compressor) As the pressure of the air increases, its temperature rises. It is essential to reduce the air temperature to avoid damage of compressor and other mechanical elements. The multistage compressor with intercooler inbetween is shown in the figure. It is used to reduce the temperature of compressed air during the compression stages. The compressed air from the first stage enters the intercooler where it is cooled. This air is given as input to the second stage where it is compressed again. The multistage compressor can develop a pressure of around 250 bar (4 stages).

Working principle of Multi-stage reciprocating compressor

Components arrangement for Multi-stage reciprocating compressor

Advantage Piston Type Compressor • Piston type compressors are available in wide range of capacity and pressure • Very high air pressure (250 bar) and air volume flow rate is possible with multi-staging. • Better mechanical balancing is possible by multistage compressor by proper cylinder arrangement. • High overall efficiency compared to other compressor

Disadvantage Piston Type Compressor • Reciprocating piston compressors generate inertia forces that shake the machine. Therefore , a rigid frame, fixed to solid foundation is often required • Reciprocating piston machines deliver a pulsating flow of air. Properly sized pulsation damping chambers or receiver tanks are required. • They are suited for small volumes of air at high pressures.

2. Diaphragm type compressor In piston compressors the lubricating oil from the pistons walls may contaminate the compressed air. The contamination is undesirable in food, pharmaceutical and chemical industries. For such applications diaphragm type compressor can be used. As the piston moves down it pulls the hydraulic fluid down causing the diaphragm to move along and the air is sucked in. When the piston moves up the fluid pushes the diaphragm up causing the ejection of air from the outlet port. Since the flexible diaphragm is placed in between the piston and the air no contamination takes place

Rotary compressor Screw-type compressor is a rotary compressor with two (2) shafts. They work according to the displacement principle and deliver continuous supply with no pulsations or pressure fluctuation. Advantages : less moving parts compared to piston type compressor. Disadvantage : Need lubricant oil to reduce friction between screw.

Rotary compressor vane compressor Sliding vane compressor is a single shaft rotary compressor which work according to the displacement principle. The air inlet is placed where the volume of the compression chamber is greatest, the outlet where the volume is smallest. Consequently, as the vanes turn, the space between them is reduced. This reduction in volume compresses the air as it travels from the inlet to the outlet.

B. Air Receiver Tank • Air Receiver provide constant air pressure in a pneumatic system, regardless of varying or fluctuating consumption. • A further function of receivers is the emergency supply to the in cases of power failure. • Air receiver should be large enough to suit the compressor flow rate, and must be matched to the selected compressor regulating system. • The size of a compressed air receiver depends on the: 1. Delivery volume of the compressor 2. Air consumption for the application 3. Network size 4. Type of compressor cycle regulation 5. Permissible pressure drop in the supply network

B. Air Receiver Tank (cont. ) Air Receiver Tank and its accessories

B. Air Receiver Tank (cont. ) An Air Receiver serves FOUR (4) main functions: • storage of compressed air, thus eliminating the need for the compressor to run continuously. • pulsation damping to smooth the pulsing flow of air from the compressor. • heat exchange to assist air cooling and thus produce condensate drop out before the air enters the distribution system. • collection and drop out point for dirt and condensate accumulating in the air after compress.

B. Air Receiver Tank (cont. ) • Receiver are usually fitted with an automatic condensate drained, or if manually operated must be periodically drained. • Air receivers must also be fitted with safety air relief valve.

C. • • • Air Dryers The service life of pneumatic systems is considerably reduced if excessive moisture is carried through the air system to the elements. It is important to fit the necessary air drying equipment to reduce the moisture content to a level which suits the application and the elements used. There are three auxiliary methods of reducing the moisture content in air: 1. Low temperature drying (coolant drying) 2. Adsorption drying 3. Absorption drying

Low Temperature Drying • • • Dew point is the temperature at which airborne water vapor will condense (100% humidity) to form liquid dew The most common type of dryer today is the refrigeration dryer. The compressed air is passed through a heat-exchanger system through which a refrigerant flow. The aim is to reduce the temperature of the air to a dew point(2˚ to 5˚) which ensure that the water in the air condenses and drops out in the quantity required. Dew point temperature is the temperature to which a gas must be cooled to condense water vapour contained in the gas. Before the compressed air is output into the network, the air is heated to bring the back to ambient conditions.

Low Temperature Drying Low temperature drying.

Adsorption Dryers Adsorption method means that the water from the air will stick to the surface of the chemicals. Usually composed of silica gel (decrease local humidity ) or activated alumina is filled into the cylinder In practice, two tanks are used. When the gel in one tank is saturated, the air flow is switched to the dry (heated). Second tank and first tank is regenerated by hot-air drying. The lowest dew point can be achieved (down to - 90˚)

Adsorption Dryers (cont. ) Schematic diagram of a heat regenerated adsorption dryer.

Absorption Drying Using wet chemical type of fluid to absorb water from the air. After absorbing this chemical water will become liquid. Among the chemicals most commonly used are urea, lithium and calcium chloride The features of the absorption process are: 1. Simple installation of the equipment. 2. Low mechanical wear because there are no moving parts in the dryer. 3. No external energy requirements

Absorption Drying (cont. ) Compressed air to flow in from the bottom of the cylinder and flows up through the absorbent material level before the dry air passes out. Chemicals that absorb moisture from the air will be moist and liquid and drip down. It is not major significance in present day practice (high operating cost & low efficiency.

D. Air Service Equipment • The final stage of compressed air servicing or conditioning is a process carried out on the air supply, directly before its point of usage. • This process is accomplished by three devices 1. Filter 2. Regulator 3. Lubricator

D. Air Service Equipment • Three aims of the air service unit is: 1. to provide the air consuming equipment (actuators, motors, air tools and control circuit) with compressed air of suitable cleanliness. 2. should also provide pressure stabilized air at no more than the required maximum pressure. 3. it provides an air supply (flow), which carries lubricating oil in the correct adjusted quantities to lubricate valves, actuators(cylinders /motors).

D. Air Service Equipment (cont. )

D. Air Service Equipment (cont. ) detailed symbol With lubricator Without lubricator simplified symbol

1. Compressed air filter • To remove all contaminants from the compressed air flowing through it (quality) as well as water which already condensed. • Liquid particles and larger particles of dirt are separated centrifugally ( due to baffles) collecting in the lower part of the filter bowl. • A further important characteristic of compressed air filters is the degree of separation, or efficiency, which indicates the percentage of particles of a particular size (as small as 5 microns) which can be separated out.

1. Compressed air filter (cont. ) Compressed air filter

2. Compressed Air Pressure regulation valve To maintain working pressure virtually constant regardless of fluctuations of the line pressure and air consumption. When the pressure is too low, it results in poor efficiencies and when the pressure is too high, energy is wasted and equipment’s performance decay faster. In pneumatic system, pressure fluctuations occur due to variation in supply pressure or load pressure. It is therefore essential to regulate the pressure to match the requirement of load regardless of variation in supply pressure or load pressure.

2. Compressed Air Pressure regulation (cont. ) Generally pressure is regulated in pneumatic system at two places. At the receiver tank In the load circuits Pressure regulation valve at the receiver tank is required as a safety measure for the system. In the load circuits, pressure regulator is used to regulate the pressure for downstream components such as valves and actuators. The best economic and technical compromise between compressedair generation and efficiency of the components is approximately: 600 k. Pa (6 bar) in the power section and 300 to 400 k. Pa (4 bar) in the control section

2. Compressed Air Pressure regulation (cont. ) Types of Pressure regulation valve Diaphragm type regulator Piston type regulator Diaphragm type regulator is commonly used in Industrial pneumatic system. There are two types of diaphragm type regulator Non- relieving or non-venting type. Relieving or venting type is commonly used

2. Compressed Air Pressure regulation (cont. ) Relieving or Venting Type Pressure regulation valve Outlet pressure is sensed by a diaphragm preloaded with a adjustable pressure setting spring. The compressed air , which flows through a controlled cross section at the valve seat, acts on the other side of the diaphragm. The diaphragm has large surface area exposed to secondary (outlet) pressure and is quite sensitive to its fluctuations. The movement of diaphragm regulates the pressure.

2. Compressed Air Pressure regulation (cont. ) If the outlet pressure is low: whenever the more compressed air is consumed on secondary side or load side, then load pressure reduces. Therefore less force acts on diaphragm. The opposing higher spring force pushes the diaphragm in such a way as to move the valve disc more and permitting more air to flow to secondary side and thus increasing the pressure again. Pressure regulator: relieving

2. Compressed Air Pressure regulation (cont. ) If the outlet pressure is high: whenever the less compressed air is consumed on secondary side or load side, then load pressure increases. Therefore more force acts on diaphragm. The opposing higher spring force pulls down the diaphragm in such a way as to move the valve disc less and permitting air to flow to vent hole and thus decreasing the pressure again Pressure regulator: relieving

3. Compressed Air lubricator To reduce friction & corrosion in air valves, linear actuator & air motors. The compressed air passing through the lubricator causes a pressure drop between the oil reservoir and the upper part of the lubricator The pressure difference is sufficient to force the oil upwards through a duct where it then drips into the nozzle. The main function of the check valve is to control the amount of oil passing through it

3. Compressed Air lubricator (cont. ) Lubricator are necessary in certain cases: i. Where extremely rapid oscillating motions are required ii. With cylinder of large diameter, lubricators should where possible be installed only directly upstream of the consuming cylinders (>125 mm)

An Industrial compressed air system.