Chapter 19. Applying Pneumatic Power. Typical Circuits and Systems

Transcription

1 Chapter 19 Applying Pneumatic Power Typical Circuits and Systems 1

2 Objectives Describe basic circuits that are frequently used to assemble complex pneumatic systems. Identify the placement and explain the function of workstation air-preparation components. Compare the design and operation of basic pressure-control circuits used in pneumatic systems. Goodheart-Willcox Co., Inc. 3 Objectives Explain the design and operation of control circuits used to regulate actuator operating speeds in pneumatic systems. Describe the operation of circuits using fourand five-port pneumatic four-way directional control valves. Goodheart-Willcox Co., Inc. 4 2

3 Objectives Explain the design and operation of basic motion-control circuits for pneumatic cylinders. Explain the design and operation of pneumatic quick-exhaust valves. Describe a two-handed safety circuit used to provide operator safety. Goodheart-Willcox Co., Inc. 5 Basic Circuits and System Analysis and Design Pneumatic systems use a number of components to produce the force and motion needed to operate a machine These components typically form basic circuit segments responsible for: Conditioning air Controlling air pressure and flow rates Producing a desired movement Goodheart-Willcox Co., Inc. 6 3

4 Basic Circuits and System Analysis and Design Pneumatic systems are typically designed using variations of basic circuit segments Familiarity with basic component and circuit segments is essential when designing pneumatic circuits or performing diagnostic and service work Goodheart-Willcox Co., Inc. 7 Workstation Air- Preparation Components Air preparation at the workstation of a pneumatic system involves: Air filtration Pressure reduction Addition of a lubricant, if needed Goodheart-Willcox Co., Inc. 8 4

5 Workstation Air- Preparation Components These air-preparation functions are performed by individual filter, pressure regulator, and lubricator components These components are often assembled into a close-fitted package This package is identified as an FRL or trio unit Goodheart-Willcox Co., Inc. 9 Workstation Air- Preparation Components The FRL (trio) unit in a basic circuit Goodheart-Willcox Co., Inc. 10 5

6 Workstation Air- Preparation Components Individual sections of FRL units may also be used at remote locations in a circuit This is done to provide appropriate air filtration, pressure control, or lubrication at all points in a circuit Goodheart-Willcox Co., Inc. 11 Workstation Air- Preparation Components A second lubricator providing additional lubrication for a remotely located cylinder Goodheart-Willcox Co., Inc. 12 6

7 Controlling System Air Pressure Air pressure in the distribution lines is higher than that required for operation of workstation circuits Reducing distribution line pressure to the level needed for the workstation: Provides a safer working pressure Increases system operating efficiency by reducing the volume of atmospheric air that must be compressed Goodheart-Willcox Co., Inc. 13 Controlling System Air Pressure The maximum operating pressure of a workstation circuit is determined by the pressure regulator in the FRL unit Pressures lower than the workstation regulator setting can be obtained using additional pressure regulators Locating these elements downstream from the FRL unit can allow actuators to function at a variety of lower pressures Goodheart-Willcox Co., Inc. 14 7

8 Controlling System Air Pressure Multiple pressures in a workstation circuit Goodheart-Willcox Co., Inc. 15 Controlling System Air Pressure Multiple pressures in a workstation circuit Goodheart-Willcox Co., Inc. 16 8

9 Controlling System Air Pressure Pilot-operated pressure regulators allow adjustment of system pressure from a remote location The use of these units allows a large, pilotoperated regulator to be close fit in the circuit, while adjustment is controlled from a remote location Goodheart-Willcox Co., Inc. 17 Controlling System Air Pressure Pilot-operated regulator application Goodheart-Willcox Co., Inc. 18 9

10 Controlling System Airflow Rate The flow rate of air to an actuator controls the operating speed of the unit Pneumatic systems use both meter-in and meter-out circuits for airflow control Meter-out circuits are preferred as the design pressurizes both sides of the actuator to provide more stable movement Goodheart-Willcox Co., Inc. 19 Controlling System Airflow Rate Meter-out circuit controlling both cylinder extension and retraction Goodheart-Willcox Co., Inc

11 Controlling System Airflow Rate The most common flow control valve in pneumatic circuits is a needle valve with an integral bypass check valve The tapered needle allows fine adjustment to provide accurate metering The check valve allows unrestricted reverse airflow through the valve Goodheart-Willcox Co., Inc. 21 Controlling System Airflow Rate Needle valves with integral check valves placed in meter-out circuits control both cylinder extension and retraction Goodheart-Willcox Co., Inc

12 Controlling System Airflow Rate The most consistent control of actuator speed is obtained when the flow control valve is located as close to the actuator as practical This is directly related to the compressibility of air The most accurate control is achieved when the controlled air volume in the actuator and lines is as low as possible Goodheart-Willcox Co., Inc. 23 Controlling System Airflow Rate When four-port, four-way directional control valves are used, flow control valves are typically placed between the actuator and directional control valve This arrangement requires the use of a flow control with an integral check valve to allow reverse airflow Goodheart-Willcox Co., Inc

13 Controlling System Airflow Rate When five-port, four-way directional control valves are used, flow control valves can be placed in the exhaust port lines of the directional control valve This arrangement eliminates the need for check valves to allow reverse flow Goodheart-Willcox Co., Inc. 25 Controlling System Airflow Rate Flow control valves with a five-port valve Goodheart-Willcox Co., Inc

14 Controlling System Airflow Rate Multiple actuator speeds require a number of airflow rates These flow rates can be produced using mechanically or solenoid-operated valves to direct airflow through a circuit Goodheart-Willcox Co., Inc. 27 Controlling System Airflow Rate Multiple flow rates providing control of cylinder extension, feed, and retraction speeds Goodheart-Willcox Co., Inc

15 Controlling Actuator Motion Control over actuator movement can involve: Simple, manually operated directional control valves Circuit segments consisting of several components using mechanically, pilot-, or solenoid-operated valves Goodheart-Willcox Co., Inc. 29 Controlling Actuator Motion Automatic cylinder return Goodheart-Willcox Co., Inc

16 Controlling Actuator Motion Continuous reciprocation of a cylinder Goodheart-Willcox Co., Inc. 31 Circuits for Other System Functions Pressure boosters can be used to produce a pressure higher than that available from distribution system Basically a small reciprocating pump Provide intensified air pressure for a segment of a circuit Goodheart-Willcox Co., Inc

17 Circuits for Other System Functions Air-to-air pressure booster Goodheart-Willcox Co., Inc. 33 Circuits for Other System Functions Quick-exhaust valves reduce back pressure in the exhaust lines of cylinders Reducing backpressure increases the operating speed of the cylinder Valves are close fit to a cylinder port to provide a direct route to the atmosphere for the exhaust air Goodheart-Willcox Co., Inc

18 Circuits for Other System Functions Quick-exhaust valve application Goodheart-Willcox Co., Inc. 35 Circuits for Other System Functions Pneumatic components can provide basic logic functions such as those used in microprocessors Functions include AND, OR, and NOR Several manufacturers produce small-moving-part pneumatic valves specifically designed for these applications These valves are combined to produce circuit control segments that produce the desired system operation Goodheart-Willcox Co., Inc

19 Circuits for Other System Functions Basic pneumatic logic circuit that provides a start/stop function from momentary valve activation Goodheart-Willcox Co., Inc. 37 Circuits for Other System Functions The sequence of operation can be timed using pilot-operated directional control valves Timing is obtained by pressurizing the valve pilots using air metered through needle valves into timing reservoirs Directional control valves shift only when the reservoir reaches the pressure level required to shift the pilot mechanism Goodheart-Willcox Co., Inc

20 Circuits for Other System Functions Basic time-delay circuit Goodheart-Willcox Co., Inc. 39 Circuits for Other System Functions Injuries to machine operators is a major concern Pneumatic circuits often include control segments that are specifically designed to reduce accidents Goodheart-Willcox Co., Inc

21 Circuits for Other System Functions A two-hand safety circuit requires an operator to use both hands to initiate and maintain machine operation These circuits will not properly function if the operator ties down one of the control valves or releases one during machine operation Goodheart-Willcox Co., Inc. 41 Circuits for Other System Functions Basic two-hand safety circuit Goodheart-Willcox Co., Inc

22 Review Question What is a logic function? Logic functions include AND, OR, and NOR functions such as used in microprocessors. They are used to provide system control. Goodheart-Willcox Co., Inc. 43 Review Question The three air-preparation components located at the workstation are often close fitted into a unit referred to as the. trio or FRL unit Goodheart-Willcox Co., Inc

23 Review Question Whenever additional pressure regulators are used downstream from the air-preparation unit, they can regulate pressures to a level the pressure setting of the workstation unit. below Goodheart-Willcox Co., Inc. 45 Review Question Where are flow control valves often placed when used with five-port, four-way directional control valves? In the valve s exhaust lines. Goodheart-Willcox Co., Inc

24 Review Question The challenge of understanding the operation of a pneumatic system can be reduced if it is considered groups of basic and working together to produce a desired result. components; subcircuits Goodheart-Willcox Co., Inc. 47 Review Question What is the purpose of a time-delay circuit? To automatically time cylinder movement. Goodheart-Willcox Co., Inc

25 Review Question Quick-exhaust valves are designed to increase the operating speed of cylinders. How is this achieved? By reducing back pressure in the exhaust lines of circuits by directly venting exhaust air to the atmosphere. Goodheart-Willcox Co., Inc. 49 Review Question In most two-hand safety circuits, what happens if one of the controls is tied down? Machine operation is partially or completely stopped. Goodheart-Willcox Co., Inc