1、FUNDAMENTALS OF GAS CONTROLS Combined Manual and Workbook EDITION III PREPARED BY Roger Carson Enterprises, Inc. FOR AMERICAN GAS ASSOCIATION 400 North. Capitol Street N.W. Washington, DC 20001 Catalog No. XH0205 Copyright 2002 by American Gas Association Third Edition July 2002 Printed in United St
2、ates of America DISCLAIMER The AGA (together with its members) disclaims liability for any personal injury, property or other damages of any nature whatsoever, whether special, indirect, consequential or compensatory, directly or indirectly resulting from the publication, use of, or reliance on this
3、 document or whether based on information contained in or omitted from this document. All warranties, express or implied, are disclaimed, including without limitation, any and all warranties concerning the accuracy of the information, its fitness or appropriateness for a particular purpose or use, i
4、ts merchantability and its non-infringement of any third partys intellectual property rights. AGA (together with its members) expressly disclaims any and all responsibilities for the accuracy or completeness of the information and makes no representations or warranties regarding the informations com
5、pliance with any applicable statute, rule or regulation. In issuing and making this document available, the AGA (together with its members) is not undertaking to render professional or other services for or on behalf of any person or entity. Nor is the AGA undertaking to perform any duty owed by any
6、 person or entity to someone else. Anyone using this document is doing so at the users own discretion and at its own risk. The user should seek the advice of a competent professional in determining the exercise of reasonable care in any given circumstances. Catalog No. XH0205 Copyright 1975, Revised
7、 July 2002 Registered by American Gas Association Printed in the United States of America Fundamentals of Gas Controls ii Fundamentals of Gas Controls EDITION III FOREWORD This manual was originally prepared under the direction of the American Gas Association and Gas Appliance Manufactures Associati
8、on Joint Committee for Customer Service. It was written by William H Thrasher, Program Manager; James C. Griffiths, Senior Research Engineer; Richard L. Weiser, Testing Department Supervisor; and J. Fred Parr, Manager of Engineering Services, American Gas Association Laboratories, Cleveland, Ohio. T
9、he 2002 Edition was edited and prepared by Mary Smith Carson, Consultant, Roger Carson Enterprises, Inc. The purpose of the manual is to provide a text for self study. Hopefully, it will become a useful tool to vocation-technical schools, appliance service and repairmen, and utility customer service
10、 programs. The text has been prepared so that only a moderate knowledge of mathematics and science is required for understanding. In an effort to assist in the reinforcement of the material found in the text, this edition updates and combines the text of the Fundamentals of Gas Controls Catalog No.
11、XH9004 manual and the Fundamentals of Gas Controls Work Book XH9203. Each chapter review has a list of the possible answers in alphabetical order on the chapter review page. Answer keys to the chapter reviews can be found on pages 136 - 141 of this manual. Other fundamental texts in this series cove
12、r the following subject areas: Gas Combustion Electricity Venting and Ventilation Gas Appliances Customer Service At the end of the text is a glossary of terms used in controls. It is suggested that the student should be familiar with these terms so that the text material will be meaningful. Words t
13、hat are defined in the glossary are noted in bold face type the first time they appear in the text.iii CONTENTS I. INTRODUCTION .1 CHAPTER REVIEW .2 II. CONTROLS AND THEIR FUNCTIONS. 3 Need for Controls.3 Manual and Automatic Operations 3 Basic Elements of Automatic Controls 4 Evolution of Automatic
14、 Controls .5 CHAPTER REVIEW .6 III. MANUAL CONTROL OF GAS APPLIANCES 8 Electric Switches9 Orifices.10 Manual Adjustment of Controllers 11 CHAPTER REVIEW .12 IV. PHYSICAL PRINCIPLES USED IN CONTROLS .16 Thermal Expansion of Gases, Liquids and Metals 16 Electrical Heating of a Resistive Element17 Chan
15、ge of Electrical Resistance with Temperature .18 Thermoelectric Effect 18 Electromagnetism and Solenoids.19 Change in Shape of Coils from Internal Pressure Changes .19 CHAPTER REVIEW .20 V. SENSING DEVICES .21 Temperature Responsive Devices 21 Bimetals .21 Unevenly Heated Shapes .23 Rod and Tube Sen
16、sors .23 Hydraulic and Pneumatic Bulbs.24 Electrical Resistance Coils, RTDs and Thermistors.24 Fusible Links24 Pressure Responsive Devices.25 Metallic Bellows and Diaphragm Sensors .25 Coiled Metallic Tubing25 Flow Sensing Devices26 Liquid Level Sensors .26 Float Type 26 Electrical Contact Type27 Fu
17、ndamentals of Gas Controls iv Rotation Sensors 27 Flame Sensors 28 Thermocouple 28 Bimetal.28 Hydraulic or Mercury VaporizationType 29 Optical Systems29 Flame Rectification29 CHAPTER REVIEW .30 VI. ACTUATION OF CONTROLS 35 Self-Powered Devices35 Use of Motion Due to Expansion or Warping .35 Use of G
18、enerated Pressure .36 Use of Generated Electrical Current 36 Externally-Powered Devices37 CHAPTER REVIEW .38 VII. AUTOMATIC CONTROLS .39 Thermostats 39 Hydraulic Thermostats.39 Rod and Tube Thermostats 39 Bimetal Thermostats 40 Heating/Cooling Thermostats 41 Automatic Offset Thermostats.42 Automatic
19、 Gas Valves .43 Diaphragm Automatic Valves43 Solenoid Valves .45 Heat Motor Automatic Valves .46 Hot-Wire Valves 46 Motorized Valves.47 Limit Controls 47 Thermostatic Limit Controls47 Low Liquid Level Shutoff Controls.49 Gas Pressure Regulators.49 Conventional Gas Pressure Regulator Operation49 Serv
20、o Pressure Regulators .51 Two-Stage Regulators51 Types of Gas Pressure Regulators .52 Capacities of Gas Pressure Regulators 54 Location and Position.54Combination Controls 55 Accessories.55 Automatic Vent Dampers.55 Motors 56 Fans or Blowers .57 Pumps.58 Fundamentals of Gas Controls v Transformers 5
21、8 Pilot Gas Filters58 Miscellaneous Controls59 Time Switches59 Draft Controls 59 CHAPTER REVIEW .60 VIII. IGNITION SYSTEMS.67 Automatic Pilots.67 Pilot Burners 67 Safety Shutoff by Automatic Pilots .69 Means of Ignition.70 Two-Stage Automatic Pilot Systems .71 Oxygen Depletion Sensing (ODS) Pilots.7
22、2 Pilot Relight Systems .73 Intermittent Ignition Devices .74 Direct Spark Ignition74 Hot Surface Ignition.75 CHAPTER REVIEW .76 IX. . APPLICATION TO APPLIANCES.79 Ranges79 Top-Burner Controls 79 Oven and Broiler Burner Controls.81 Modulating Oven Control Systems81 Cycling Oven Control Systems81 Bro
23、iler Burner Controls .82 Self-Cleaning Oven Controls.83 Ranges Features and Accessories 84 Programmed Cooking84 Roast or Meat Probes .85 Timers and Clock Controls 85 Rotisseries 86 Lights .86 Automatic Water Heaters.88 Automatic Storage Heaters 88 Energy Devices 88 Temperature and Pressure Relief Va
24、lve.88 Automatic Circulating Tank Type Heaters 89 Instantaneous Water Heaters90 Swimming Pool Heaters 90 Central Heating Systems90 Steam Heating90 Steam Boiler Safety Controls and Limits 91 Fundamentals of Gas Controls vi Hot Water (Hydronic) Heating 91 Hydronic Zone Control93 Warm Air Heating93 War
25、m Air Furnace Ignition93 Warm Air Heating Fan/Limit Controls 94 Potable Water-Source Space Heating Systems94 Room Thermostats .95 Humidity Control.96 Conversion Burners96 Wiring Considerations .97 Line Voltage Control Circuits97 Low Voltage Control Circuits97 In-Space Heating Appliances.98 Outdoor H
26、eating.98 Clothes Dryers99 Ignition Systems.99 Dryness Sensing.101 Thermostats 101 Moisture Sensors101 Timers 102 Temperature Limit Controls .102 Two-Level Dryer Burners 103 Air Flow Control103 Motor Control 103 Refrigeration 104 Refrigerator Burners 104 Burner Orifice 105 Pressure Regulators105 The
27、rmostats 105 Defrost Systems .105 Incinerators 106 Ignition of Refuse.106 Controls106 Air Conditioners.106 Ignition.107 Cooling Thermostats107 Pilot and Main Burner Valves108 Venting.108 Sail Switch for Flue Gas 108 Limits 108 Low Temperature Limit-Evaporator, Chilled Water .108 High Temperature Lim
28、it-Generator.109 Flow Rate Switch for Chilled Water109 High Pressure Relief Valve109 Special Considerations .109 Motors 109 Fundamentals of Gas Controls vii Fan Capacity109 Water Pump Capacity110 CHAPTER REVIEW .111 X. MAINTENANCE AND REPAIR OF CONTROLS .126 Preventive Maintenance.126 Summary Commen
29、ts127 CHAPTER REVIEW .128 REFERENCE SOURCES129 GLOSSARY 130 ANSWERS TO CHAPTER REVIEW 136 Fundamentals of Gas Controls 1 I. Introduction When man discovered fire, he soon discovered that he could make a fire larger by adding fuel, smaller by removing fuel, and put it out by covering the fire with an
30、 animal skin or dirt or pouring water on it. Only by controlling the fire was he able to make it serve him. When fire was used for cooking or heating of a hut or tent at least some rough control was essential for the fire to be of use. The most primitive and easiest way to control the fire, of cours
31、e, was to regulate the amount of fuel and the rate new fuel was added to the fire. Soon, since combustion of fuel doesnt take place without air, man learned that by changing the amount of air supplied to a fire, the rate of burning or intensity could be changed. Early wood or coal stoves and furnace
32、s used this idea. They had dampers in the vent pipes and adjustable openings in the firebox for heat control. Later, stokers were used on coal furnaces, which could be adjusted to feed coal at almost any desired rate. As liquid and gaseous fuels came into wider use and electricity had begun to be wi
33、dely distributed, man was able to apply his technical knowledge to developing automatic devices, which would start the combustion and control it without his attention. This manual describes the devices used in gas appliance controls*, how they work, on what principles they work, and how they are app
34、lied in systems to provide automatic control of residential gas appliances. * Words, which are defined in the glossary, are noted in boldface type the first time they appear in the text. Fundamentals of Gas Controls 2 CHAPTER REVIEW I. Introduction This review is designed to be a reinforcement of th
35、e information supplied in each chapter. Instructions: Read one chapter of the manual and read the questions in the Chapter Review. Read question and provide an answer in your mind before completing the blank spaces provided. The answers to each page are provided in the column to the far right, howev
36、er, they are not in order. It is your job to select the correct word or words and fill-in the blanks. The correct answers are listed by the numbers at the end of the manual. If you are not correct, review the section of the manual that pertains to that question. EXAMPLE: QUESTION ANSWER KEY 1. DAMPE
37、RS FOR WOOD STOVES AND 2. STOKERS ON COAL FURNACES ARE TWO EXAMPLES OF EARLY CONTROLS USED BY MAN FOR HEATING APPLIANCES. (p. 1) DAMPERS STOKERS Fundamentals of Gas Controls 3 II. Controls and Their Functions NEED FOR CONTROLS With a few exceptions, such as fue l cells, gas appliances are based on t
38、he utilization of heat energy produced by burning the gas fuel. Every control function relates in some way to turning on or turning off the supply or otherwise regulating the flow of gas into the appliances. Some controls act directly on gas flow. For example, a furnace thermostat acts to cause the
39、gas flow to begin or stop. Some controls act in response to the gas flow, for example, a fan switch on a forced air furnace is activated when fuel is burned and heat is produced. Some controls act to begin or stop the gas flow; others act because of it. Controls whose functions are to cause the appl
40、iance to operate for its intended service are called operating controls. Those whose function is to prevent or curtail a hazardous operation are called safety controls. Sometimes a control will function in both of these capacities. Operating controls regulate operation of appliances (such as furnace
41、s) by controlling the flow of fuel (as by thermostats), and other appliance mechanisms (such as fans) which are needed to maintain proper functioning. These operating controls allow unattended (automatic) operation of appliances and help the appliance or equipment to operate in a safe and efficient
42、manner. The foremost need for controls on gas appliances is safety. Gas fuel is a safe and useful servant of man but without precautions, hazards are possible. Safety controls are, therefore, applied to gas appliances, which are intended to override or act independently of operating controls to prev
43、ent a hazardous condition. These safety controls are of the type that shut down equipment or act to relieve excessive temperature or pressure conditions. MANUAL AND AUTOMATIC OPERATION Gas is supplied to appliances through pipes. The valve controlling the gas flow through the pipe, therefore, is the
44、 heart of the gas appliance control system. In the simplest case, the valve is operated by hand (this is called a manual control system). An example is the range-top burner. When operating this burner, the user judges the amount of heat required, and, while watching the flame, adjusts it to the desi
45、red size by turning a knob connected to a gas valve. Manual control is simple and relatively inexpensive. Automatic control is used in most applications of modern appliances. For example, virtually all water heaters sold today are automatic compared to manual operation of over 40 years ago. This has
46、 been made possible by simple, reliable designs of controls and mass production techniques. The range-top burner also has Fundamentals of Gas Controls 4 been fitted with automatic controls in the form of automatic reignition or in some older models the “Burner-with-a-Brain.”* Automatic devices in th
47、is system perform the same task as the user does when exercising manual control. Many central heating systems are controlled with setback thermostats, which automatically change the temperature settings on the thermostat controls during selected periods such as when no one is at home or at night. In
48、 some appliances, manual control is impractical or even impossible. It may be impractical because of safety, a complex ignition or operating sequence, or accessibility to the appliances. Automatic control systems are used most often because they are far superior to manual control in the safe and eff
49、icient utilization of gas. BASIC ELEMENTS OF AUTOMATIC CONTROLS In every control system, three elements are required. These are illustrated in Figure l. First, there must be a device that senses the conditions of operation. In manual control, the eye is used to observe. When the range-top burner is operated, the user will note visually that water is or is not boiling, or the condition of the cooking food. This function is performed in the “Burner-with-a-Brain” system by a sensing device or sensor touching the bottom of the cooking utensil. The actual contr
