Source of Pneumatic Power

Source of Pneumatic Power
Chapter 13, Part 1 Source of Pneumatic Power Compressed-Air Unit and Compressor

Objectives Describe the function of a compressed-air unit.
Name and explain the function of each of the components in a compressed-air unit. Identify the basic designs used in air compressor construction. Compare the operating characteristics of positive- and non-positive-displacement air compressors.

Objectives Compare the operating characteristics of rotary and reciprocating air compressors. Describe the general construction characteristics of the various compressor types. Explain the operation of the various systems used to control the maximum air pressure available from the compressed-air unit.

Objectives Identify the factors that must be considered to estimate the required output of a compressor to meet the air demands of a pneumatic system. Interpret performance data supplied by a compressor manufacturer.

Compressed-Air Unit The source of compressed air for a pneumatic system is the compressed-air unit Prime mover Compressor Other components to condition and store the pressurized air used by the system workstations Compressed air units vary in size

Compressed-Air Unit Very small packages may produce only a fraction of a cubic foot of air per minute (cfm) DeVilbiss Air Power Company

Compressed-Air Unit Large, industrial units may produce thousands of cfm Badger Iron Works, Inc.

Compressed-Air Unit Compressed-air units can be classified as portable units or central air supplies Physical size is not the only factor in placing a unit in one of these classes Easy transport of a unit from one location to another is a more important factor Many portable units have a larger capacity than many stationary central air supplies

Compressed-Air Unit A portable unit may be large or small

Compressed-Air Unit Portable units allow the compressor to be moved to the work site Atlas Copco

Compressed-Air Unit A compressed-air unit consists of: Prime mover
Compressor Coupling Receiver Capacity-limiting system Safety valve Air filter May have a cooler and dryer

Compressed-Air Unit The prime mover in a compressed-air unit may be:
Electric motor Internal combustion engine Steam or gas turbine A coupling connects the prime mover to the compressor

Compressed-Air Unit Belt coupling DeVilbiss Air Power Company

Compressed-Air Unit Mechanical coupling DeVilbiss Air Power Company

Basic Compressor Design
A variety of designs are used for air compressors in the compressed-air unit Reciprocating piston Rotary, sliding vane Rotary screw Dynamic

Reciprocating-piston compressors are the most common Rotary screw compressors are popular in new installations

Inline, reciprocating compressor DeVilbiss Air Power Company

The basic operation of any compressor includes three phases Air intake Air compression Air discharge Component parts and physical operation varies between compressor designs

Basic Compressor Classifications
Compressors are classified as: Positive or non-positive displacement Reciprocating or rotary Positive-displacement compressors mechanically reduce the compression chamber size to achieved compression Non-positive-displacement compressors use air velocity to increase pressure

Basic Compressor Classifications
A reciprocating compressor has a positive displacement DeVilbiss Air Power Company

Compressor Design and Operation
Reciprocating compressors use a cylinder and a reciprocating piston to achieve compression Rotary compressors use continuously rotating vanes, screws, or lobed impellers to move and compress the air

Reciprocating compressors are commonly used in pneumatic systems Very small, single-cylinder, portable compressors for consumer use Large, industrial, stationary units may produce thousands of cubic feet of compressed air per minute

Large, industrial, reciprocating compressor Atlas Copco

Reciprocating compressors are available in single- or multiple-cylinder designs Multiple cylinders may be arranged as: Inline Opposed V type W type Other cylinder configuration

Inline reciprocating compressor DeVilbiss Air Power Company

V-type reciprocating compressor DeVilbiss Air Power Company

Reciprocating compressors use a single-acting or double-acting compression arrangement Single-acting compressors compress air during one direction of piston travel Double-acting compressors have two compression chambers, allowing compression on both extension and retraction of the piston

Double-acting compressor

Rotary, sliding-vane compressors use a slotted rotor containing movable vanes to compress air Rotor is placed off center in a circular compression chamber, allowing the chamber volume to change during rotation These volume changes allow the intake, compression, and discharge of air during compressor rotation

Centrifugal force keeps the vanes in contact with the walls

Rotary screw compressors use intermeshing, helical screws to form chambers that move air from the atmosphere into the system on a continuous basis This produces a nonpulsating flow of air at the desired pressure level

Rotary screw compressors have intermeshing, helical screws Atlas Copco

Rotary screw compressors have become popular for larger industrial installations Lower initial cost Lower maintenance cost Adaptable to sophisticated electronic control systems

Sliding vane and screw compressor designs often inject oil into the airstream moving through the compressors Reduces wear on vane and screw contact surfaces Improves the seal between the surfaces Oil is removed by a separator to provide near-oilless compressed air for the pneumatic system

The basic operating theory of dynamic compressors is converting the kinetic energy of high-speed air into pressure Dynamic compressor designs are either: Centrifugal Axial

Centrifugal dynamic compressor: An impeller increases airspeed Prime mover energy is converted into kinetic energy as airspeed rapidly increases through the impeller Kinetic energy is converted to air pressure as air movement slows in the volute collector

Centrifugal dynamic compressor

Impeller assembly of a centrifugal dynamic compressor

Axial-flow dynamic compressor: Rotating rotor blades increase airspeed Fixed stator blades decrease airspeed Kinetic energy is converted to air pressure Series of rotor and stator sections are staged to form the axial-flow compressor

Axial-flow dynamic compressor

Pressure is created when high-speed air is slowed by the fixed stator blades

Dynamic compressor designs are used to compress air and other gases for large, industrial applications Oil refineries Chemical plants Steel mills

Lobe-type compressors consist of two impellers with two or three lobes that operate in an elongated chamber in the compressor body Spinning impellers trap air in chambers that form between the lobes As the impellers turn, this trapped air is swept from the inlet port to the outlet port to increase system pressure

Impellers from a lobe-type compressor Atlas Copco

Lobe-type compressors are often called blowers They are typically used in applications requiring air pressure of only 10 to 20 psi

Compressor staging involves connecting a number of basic compressor units in series to raise air pressure in small increments This method permits easier control of air temperature, which results in more-efficient compressor package operation

Inline, staged, reciprocating compressor DeVilbiss Air Power Company

Compressor-Capacity Control
Compressor-capacity control refers to the system that matches the compressed-air output to the system-air demand The better the air output of the compressor matches system consumption, the more cost effective the operation of the system

Compressor-capacity control systems include: Bypass Start-stop Inlet valve unloading Speed variation Inlet size variation

Bypass control uses a relief-type valve to exhaust excess air Air is continuously delivered to the system at the compressor’s maximum flow rate This type of control is not considered desirable as it is inefficient

Start-stop capacity control is commonly used with small, electric motor-driven compressor packages that operate pneumatic systems consuming air on an intermittent basis

Start-stop control uses a pressure-sensitive switch to start and stop the compressor to maintain a preselected pressure range

Start-stop control: compressor start

Start-stop control: compressor stop

Inlet valve unloading controls compressor output by holding the inlet valve open whenever maximum system pressure is achieved Allows the prime mover to operate continuously Can be used in systems having internal combustion engines or electric motors as the prime mover

Varying compressor speed can control compressor capacity Can be used with reciprocating and rotary compressor designs Primarily used on large, industrial installations Sensors monitor pressure and send a signal to control compressor speed

Varying the size of the compressor inlet can control compressor capacity Compressor operates at a constant speed The volume of air that can enter the compressor is restricted Output varies with the size of the inlet Primarily used on dynamic compressors

Selecting a Compressor Package
Establishing the level of system air consumption is a key factor when selecting a compressor This can be accomplished by identifying: Actuators used in the system Compressed-air needs of each item Percentage of time each functions

Selecting a Compressor Package
Other factors must be considered during system compressor selection Compressor and prime mover type Method of compressor-capacity control Auxiliary controls such as coolers, separators, and driers System instrumentation

Gay-Lussac’s Law Charle’s Law Boyle’s Law

Review Question Compressed-air units may be classified as a(n) _____ or _____. portable unit; central air supply

Review Question List the components found in a typical compressed-air unit and describe their function. A. Prime mover to supply system energy; B. coupling to mechanically connect prime mover and compressor; C. compressor to pressurize atmospheric air; D. receiver to store conditioned air; E. capacity-limiting switch to limit the maximum pressure produced by the compressor; F. safety valve to vent pressure if the capacity-limiting switch fails; and G. may also include filters, coolers, and dryers.

Review Question The simplest compressor in both design and operating theory is the single-acting, _____ compressor. reciprocating

Review Question Dynamic compressors can also be classified as _____-displacement compressors. non-positive

Review Question The continuous rotating motion of the compression elements identifies a(n) _____ compressor design. rotary

Review Question Describe the double-acting compressor design.
A connecting rod and crosshead are used to convert the rotary motion of the crankshaft to the reciprocating motion. Compression chambers on either side of the piston allow compression and intake during each piston stroke.

Review Question In a two-stage, reciprocating compressor, the outlet port of the first compression chamber is connected to the _____ port of a second compression chamber. inlet

Review Question Compressor-air output and system-air demand are matched by using some type of _____ system. compressor-capacity control

Review Question Name four factors that make selecting a compressor difficult. A. The variety of compressor designs, B. load variations in a pneumatic system, C. the variety of auxiliary equipment available, and D. demands of future growth of the system.

Glossary Air filter Capacity-limiting system
A component designed to remove solid particles, moisture, and/or lubricant from pneumatic system air. Capacity-limiting system A system used to control the maximum air pressure produced by the pneumatic system compressor. Compressor start-stop, inlet valve unloading, and other methods can control capacity.

Glossary Compressed air unit
Commonly used to designate a pneumatic compressor station that includes a prime mover, compressor, reservoir, and pressure control components.

Glossary Cooler Coupling
A pneumatic system dryer that uses a refrigeration element to lower the temperature of system air for the purpose of removing moisture. Coupling A general term used for devices that connect system components such as fluid conductors and power transmission shafts.

Glossary Double-acting compressor
A compressor design in which air intake and compression are completed in chambers located on both the top and underside of the compressor pistons. These compressors were common in larger industrial installations, but are being replaced by current rotary designs.

Glossary Dryer The pneumatic system component designed to remove water vapor from the compressed air. The unit is usually located in the compressor station area and may use refrigeration, chemical, or mechanical means to reduce the water content of the air.

Glossary Dynamic compressor
A device that compresses air or other gas using rotating vanes or impellers. These moving components increase pressure by converting the energy in the high velocity air to pressure.

Glossary Lobe-type compressor
Usually provide only low-pressure air. Construction involves specially-designed elements with lobes that provide a sealed pumping chamber. Air is swept from the compressor inlet to the outlet as the lobes rotate. Often referred to as blowers.

Glossary Non-positive-displacement compressor Positive displacement
A compressor that does not have a variable-volume pumping chamber. An impeller or other device is used to move the fluid. The inertia of that fluid movement produces pressure when flow is resisted. Positive displacement A pump or rotary actuator design with a positive seal between the inlet and outlet, which produces a constant volume of fluid for each revolution.

Glossary Prime mover Receiver
The source of energy for any fluid power system. Commonly used prime movers are electric motors and internal combustion engines. Receiver A tank in a pneumatic system, located close to the compressor, that stores and assists in conditioning compressed air.

Glossary Reciprocating compressor
A common compressor design using a cylinder, piston, crankshaft, and valves similar to an internal combustion engine. The reciprocating action of the piston brings air into the cylinder, where it is compressed and then moved into the system.

Glossary Rotary compressor
A compressor design that compresses air using a continuous process rather than the stop-and-go action of a reciprocating unit. Examples include positive-displacement screw and vane units and non-positive-displacement centrifugal and axial-flow dynamic compressors.

Glossary Rotary screw compressor
A compressor unit that uses intermeshing screws to form chambers that linearly move air through the compressor. The design provides a continuous, positive displacement of the air.

Glossary Rotary sliding-vane compressor
A compressor unit using a rotor with chambers separated by sliding vanes. Turning the unit produces an almost pulsation-free stream of compressed air.

Glossary Single-acting compressor
A reciprocating-piston compressor in which intake and compression occur in the cylinder space above the piston during one rotation of the compressor crankshaft. The design may contain multiple cylinders, but the cylinders are not staged.

Glossary Staging A process commonly used in the design of pneumatic compressors where the outlet of one compressor cylinder is connected to the intake of the next cylinder to obtain higher system pressures.

Chapter 13, Part 2 Work Performers of Pneumatic Systems
Cylinders, Motors, and Other Devices

Objectives Describe the construction features of basic, pneumatic linear and rotary actuators. Compare the design and operation of pneumatic cylinders. Compare the design and operation of pneumatic motors. Explain the performance characteristics used to rate the operation of pneumatic motors.

Objectives Describe the basic design and operation of specialized pneumatic tools commonly used in consumer and industrial applications. Size pneumatic cylinders and motors to meet the force and speed requirements of a basic work application. Interpret manufacturer specifications for basic, pneumatic cylinders, motors, and power tools.

Pneumatic Actuators Pneumatic systems convert the potential energy of compressed air into force and movement using: Cylinders Motors Variety of other specially designed actuators and processes

Pneumatic Actuators Cylinders provide straight-line movement and force for use in mechanically operated equipment Often called linear actuators Force generated is controlled by system pressure Speed of movement is determined by the volume of air allowed to enter the unit

Pneumatic Actuators Pneumatic motors convert the potential energy of compressed air into torque and rotary movement Often called rotary actuators Torque depends on air pressure and the internal structure of the motor Operating speed is determined by the internal displacement of the motor per revolution and the volume of compressed air passing through the motor

Pneumatic Actuators Other processes and actuator designs use compressed air to assist in or complete a task Reciprocating movement Process assistance Nozzles Impact tools

Pneumatic Cylinder Construction
Typical pneumatic cylinders Parker Hannifin

The basic structure of pneumatic cylinders is very similar to those used in hydraulic systems Lower system operating pressures allow the use of lighter materials in pneumatic-system components Water vapor present in compressed air requires the use of corrosion-resistant materials or coatings for component parts

Basic pneumatic cylinder construction IMI Norgren, Inc.

Some manufacturers produce nonlubricated pneumatic cylinders Do not require the addition of oil to the system compressed air Special coatings on the surface of the cylinder bore and other bearing surfaces provide lubrication Coatings are not scraped off during the operation of the actuator

Resilient seals prevent both internal and external leaks IMI Norgren, Inc.

Pneumatic cylinders may be single or double acting The operating principles of single-acting and double-acting pneumatic cylinders are basically the same as the cylinders designed for hydraulic applications

Typical, single-acting cylinder IMI Norgren, Inc.

The construction techniques used to manufacture pneumatic cylinders are very similar to those used to produce hydraulic cylinders Lower operating pressures allow some difference in construction Cylinder ends and barrel may be attached by metal rolling, rather than with tie rods, threads, or snap rings

Rolled-metal ends on a cylinder Parker Hannifin

Pneumatic Cylinder Sizing
Two factors are basic to determining required actuator size Cylinder force output Absolute air consumption required to produce desired system performance

The force output of a cylinder is determined by system air pressure and the effective area of the cylinder piston F = P × A

Air consumption of a cylinder can be estimated Calculate the volume of air displaced during one cycle of the cylinder Multiplying it by the number of cycles per minute and the absolute pressure ratio CFM = V × Pr × N

Two factors make the accurate calculation of air consumption in a pneumatic system difficult Air leaks Variations in the actual volume of cylinder air chambers

Manufacturers provide a variety of specific information about the cylinders they produce Construction materials Available sizes Pressure ratings Specific features such as cushions and mountings

Pneumatic Rotary Motors
Typical rotary motors Atlas Copco

Pneumatic motors are used to power: Many large stationary machines A large variety of portable hand tools These motors range in size from fractional-horsepower units to motors producing over 50 horsepower

Air motors are available in many designs Vane Piston Turbine Other, specialized designs The vane air motor is the most common design

Vane motors can be found in hand tools and large, stationary installations Atlas Copco

Operation of a vane motor

Piston air motors are most often found in installations requiring higher horsepower output They are available in both axial and radial piston designs

Parts of an axial-piston motor

Turbine motors incorporate air nozzles to direct air onto a turbine Nozzle produces high-speed air, which results in very high output-shaft speeds In specialized applications, the speed of turbine motors can reach 100,000 rpm

Turbine air motor Atlas Copco

Most manufacturers of rotary air motors publish tables and graphs that provide details about: Horsepower Torque Air consumption These data cover a wide range of operating speeds

Pneumatic Reciprocating Motors
Pneumatic reciprocating motors use percussive or nonpercussive techniques to transfer energy from compressed air to a workpiece Percussive tools provide multiple, physical impacts to overcome resistance Nonpercussive devices generally repeat a cycle to provide linear motion that is used to directly operate a machine

Total input force of a percussion-type reciprocating motor is determined by: System air pressure Area of the piston

The paving breaker is a very common application of a reciprocating motor Often called a jackhammer Used in a number of applications Models available ranging in size from hand tools to large units mounted on mobile support equipment

Example of a reciprocating motor Atlas Copco

Reciprocating motors are used to power a variety of tools found in the foundry, construction, and general metal fabrication industries Sealing hammers Chipping hammers Riveting hammers Tampers Rammers

Chipping hammers are used in foundries Atlas Copco

Using a tamper on a casting mold Badger Iron Works, Inc.

Reciprocating motors commonly operate from under 1000 to over 3000 movements per minute of operation The operating rate depends on the task performed and the type of material being cleaned, formed, or trimmed

Other Pneumatic-Powered Functions and Equipment
Compressed air is often used to assist functions without applying force to linear or rotary actuators Spraying Drying Material agitation Material transfer

Insecticide is usually sprayed USDA

Compressed air is used to agitate material Assure proper mixing of liquids Prevent the settling of solid materials in a suspension Provide oxygenation

Agitation is used in sewage treatment

A nozzle is a very important device in many systems using compressed air In turbine motors, nozzles produce rapid airflow to assure the high speed rotation of the turbine output shaft Nozzles may be convergent or convergent-divergent

Nozzle designs

A blowgun is a simple example of a nozzle IMI Norgren, Inc.

Blowguns are simple tools, but must be very carefully handled Produce high air velocity Can cause serious injury Designs are available with a bleed-off to increase safety

Bleed-off safety feature on a blowgun IMI Norgren, Inc.

Pneumatic-powered impact wrenches are commonly used in service and manufacturing industries These tools are used to tighten or remove bolts and nuts

Construction of an impact wrench Chicago Pneumatic

Parts of a pneumatic impact wrench Chicago Pneumatic

Nutsetters are specialized impact wrenches for installing multiple fasteners Atlas Copco

Nail drivers are used to install staples, nails, or other fasteners in wood and other materials Pneumatic models have become popular for use by general consumers, as well as by the construction industry

Typical pneumatic nail driver

Pneumatic powered nail drivers use high-impact force from an air-driven piston and piston rod to quickly and easily install fasteners Caution: special care must be taken to prevent the accidental discharge of these units, which can cause injury

Pneumatic nailer at idle Chicago Pneumatic

Pneumatic nailer when actuated Chicago Pneumatic

Pneumatic rock drills are commonly used in quarries, mining, and road construction The holes bored by this equipment are used for the placement of explosive charges that break the rock along a line connecting the holes

Pneumatic rock drill Atlas Copco

Pneumatic-powered gripping tools are used by robotic equipment to handle materials Robot is responsible for accurately locating and then opening and closing the gripper Gripper must provide accurate clearances and grip forces

Grippers are used by industrial robots

Grippers are often designed for a specific application IMI Norgren, Inc.

Review Question Because of the relatively low operating pressure of pneumatic cylinders, metal _____ techniques can be used to permanently attach the barrel to the cylinder head and cap. rolling

Review Question What are the four primary types of information provided by cylinder manufacturers in their catalogs and data sheets? A. Construction materials, B. available sizes, C. pressure ratings, and D. features.

Review Question List three performance factors that make piston air motors desirable in many pneumatic system applications. A. High power output, B. high starting torque, and C. accurate speed control.

Review Question What determines the speed of an air motor?
The displacement of the motor and the volume of air that is metered through the unit.

Review Question Name six tools that use reciprocating motors to power their operation. A. Paving breaker (or jackhammer), B. Scaling hammers, C. chipping hammers, D. riveting hammers, E. tampers, and F. rammers.

Review Question An air motor should be sized to operate on what fraction of the workstation pressure to allow for the extra power needed for starting loads and unexpected overloads? 2/3

A. Air pressure and B. piston area.
Review Question Identify the two factors that determine the impact force of a percussive, reciprocating air motor. A. Air pressure and B. piston area.

Glossary Air nozzle Blowgun
A device located on the end of an air line and containing an outlet orifice designed to maximize kinetic energy from the controlled release of pressurized system air. Often used in a blowgun. Blowgun A device containing an air nozzle and designed for cleaning parts and equipment with a high-velocity airstream.

Glossary Chipping hammer Force
A handheld, pneumatic, reciprocating tool designed to chip material from concrete, masonry, plaster, or other substances. Force An influence on a body that causes it to accelerate (move).

Glossary Gripper Impact wrench
An actuator commonly used with robots to handle parts in machining or assembly operations. Impact wrench A portable hand tool, often operated by compressed air, used to install or remove bolts or nuts with a series of rapid-impact, rotary blows.

Glossary Linear actuator Material agitation
A term often used to indicate a hydraulic or pneumatic cylinder. It converts fluid pressure and flow into linear mechanical force and movement. Material agitation The use of compressed-air systems to mix or compact materials in process, packaging, or other industries.

Glossary Material transfer Metal rolling
The use of compressed-air systems to move powder or small-particle materials through tubes from one process or storage point to another. Metal rolling A metal-forming technique that is used by some manufacturers to attach the barrel to the cap and rod ends of the cylinder.

Glossary Nail driver Nut setter
A portable pneumatic tool used to drive nails. Nut setter A specialized pneumatic impact wrench designed for assembly line work. The device installs nuts on bolts and torques them to a specified tightness. Available in single- and multiple-driver heads.

Glossary Paving breaker
A pneumatic percussion tool used for breaking pavement, compacted soil, and a variety of other materials or processes. The unit may be handled by an individual operator or mounted on mobile equipment.

Glossary Pneumatic reciprocating motors Rammer
Air-powered motors that produce a repeated back-and-forth, linear motion. For example, this type of motor powers a jackhammer used in street maintenance. Rammer A pneumatic, portable, reciprocating tool used to compact sand in foundry molds and other applications.

Glossary Riveting hammer Rock drill
A pneumatic, portable, reciprocating tool used to place and form the end of rivets. Rock drill A pneumatic tool often used to make rock cuts in quarries, mines, and highway construction. May use a drill or a percussion tool for cutting.

Glossary Rotary actuator Scaling hammer
A fluid power actuator used to produce torque and rotary motion. Commonly called a hydraulic motor or pneumatic motor. Scaling hammer A pneumatic, reciprocating hand tool used to remove flux and spatter from welds in fabricated products.

Glossary Spraying Tamper
A process function involving the use of compressed air to apply paint, agricultural chemicals, or other materials. Tamper A portable, pneumatic, reciprocating tool used to compact dirt at construction sites and other applications.

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