Source of Pneumatic Power Chapter 15 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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressed-Air Unit Very small packages may produce only a fraction of a cubic foot of air per minute (cfm) DeVilbiss Air Power Company © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressed-Air Unit Large, industrial units may produce thousands of cfm Badger Iron Works, Inc. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressed-Air Unit A portable unit may be large or small © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressed-Air Unit Portable units allow the compressor to be moved to the work site Atlas Copco © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressed-Air Unit Belt coupling DeVilbiss Air Power Company © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressed-Air Unit Mechanical coupling DeVilbiss Air Power Company © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Basic Compressor Design Reciprocating-piston compressors are the most common Rotary screw compressors are popular in new installations © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Basic Compressor Design Inline, reciprocating compressor DeVilbiss Air Power Company © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Basic Compressor Design The basic operation of any compressor includes three phases Air intake Air compression Air discharge Component parts and physical operation varies between compressor designs © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Basic Compressor Classifications A reciprocating compressor has a positive displacement DeVilbiss Air Power Company © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation 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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation Large, industrial, reciprocating compressor Atlas Copco © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation 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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation Inline reciprocating compressor DeVilbiss Air Power Company © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation V-type reciprocating compressor DeVilbiss Air Power Company © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation 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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation Double-acting compressor © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation 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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation Centrifugal force keeps the vanes in contact with the walls © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation 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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation Rotary screw compressors have intermeshing, helical screws Atlas Copco © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation Rotary screw compressors have become popular for larger industrial installations Lower initial cost Lower maintenance cost Adaptable to sophisticated electronic control systems © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation 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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation 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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation 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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation Centrifugal dynamic compressor © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation Impeller assembly of a centrifugal dynamic compressor © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation 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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation Axial-flow dynamic compressor © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation Pressure is created when high-speed air is slowed by the fixed stator blades © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation Dynamic compressor designs are used to compress air and other gases for large, industrial applications Oil refineries Chemical plants Steel mills © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation 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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation Impellers from a lobe-type compressor Atlas Copco © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation Lobe-type compressors are often called blowers They are typically used in applications requiring air pressure of only 10 to 20 psi © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation 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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor Design and Operation Inline, staged, reciprocating compressor DeVilbiss Air Power Company © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor-Capacity Control Compressor-capacity control systems include: Bypass Start-stop Inlet valve unloading Speed variation Inlet size variation © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor-Capacity Control 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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor-Capacity Control Start-stop capacity control is commonly used with small, electric motor-driven compressor packages that operate pneumatic systems consuming air on an intermittent basis © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor-Capacity Control Start-stop control uses a pressure-sensitive switch to start and stop the compressor to maintain a preselected pressure range © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor-Capacity Control Start-stop control: compressor start © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor-Capacity Control Start-stop control: compressor stop © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor-Capacity Control 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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor-Capacity Control 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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Compressor-Capacity Control 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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Review Question Compressed-air units may be classified as a(n) _____ or _____. portable unit; central air supply © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Review Question The simplest compressor in both design and operating theory is the single-acting, _____ compressor. reciprocating © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Review Question Dynamic compressors can also be classified as _____-displacement compressors. non-positive © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Review Question The continuous rotating motion of the compression elements identifies a(n) _____ compressor design. rotary © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Review Question Compressor-air output and system-air demand are matched by using some type of _____ system. compressor-capacity control © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Glossary Compressed air unit Commonly used to designate a pneumatic compressor station that includes a prime mover, compressor, reservoir, and pressure control components. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.