Mobile Equipment Hydraulics: A Systems and Troubleshooting
Contents
1. Figure 1 3 Locking out the operating controls for fluid power systems ensures that the machinery cannot be operated while maintenance or repairs are being performed Tagging the lock and or operating controls provides anyone attempting to operate the equipment with a warning and infor mation about who to contact An Overview 3 Copyright 2010 Cengage Learning All Rights Reserved May not be copied scanned or duplicated in whole or in part Due to electronic rights some third party content may be suppressed from the eBook and or eChapter s Editorial review has deemed that any suppressed content does not materially affect the overall learning experience Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it Licensed to iChapters User each must also place his or her own lock and tag on the energy isolating device or devices No lock out tag out program should be built using the steps earlier outlined exclusively A qualified committee that includes safety professionals should always determine and approve the exact process for any business school or agency TO GET STARTED Like many technologies that make significant contributions to our world today it is impossible to point to one date or person that invented the technol ogy Hydraulics has much of its beginning in the work of Archimedes an inventor and scientist from the third century BCE Some also speculat2. cations this measurement is usually described in pounds per square inch The metric measurement is usually stated in bar A bar is a pressure equal to 1 million dynes per square centimeter Force Figure 1 6 Force is the ability to do work In a hydraulic system we use force to transfer power from one place to another within the system Force is a function of pressure being applied over an area Figure 1 7 Area is a measurement of the exposed face of a surface In the case of fluid power systems when a fluid under pressure is in contact with a surface a force is produced The amount of the force is equal to the area of the surface times the pressure Figure 1 8 Pressure is the force being applied over a unit of area As a submarine descends into a body of water the water surrounds the submarine and applies a force equal in all directions The amount of force acting on a square unit of measure such as square inches or square centimeters is called pressure An Overview 5 Copyright 2010 Cengage Learning All Rights Reserved May not be copied scanned or duplicated in whole or in part Due to electronic rights some third party content may be suppressed from the eBook and or eChapter s Editorial review has deemed that any suppressed content does not materially affect the overall learning experience Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it License
3. it typically means that the diameter of the cylinder is 6 inches Figure 1 11 Volume is a function of area multiplied by length The first thing that needs to be calculated is the cross sectional area of the cylinder This is done by multi plying the ratio of a circle s diameter to its circumfer ence also known as Archimedes constant or pi by the square of the radius of the cylinder and then taking that result and multiplying it by the length Figure 1 12 It sounds more difficult than it actually is Follow these steps 1 Measure the diameter of the cylinder In this case 6 inches 2 Divide by 2 to find the radius This would be 3 inches 3 Multiply the result by itself In this case 3 times 3 equals 9 This process is called squaring the number 4 Multiply the square of the radius 9 by pi p In almost all hydraulic system calculations pi is rounded to either 3 14 or 3 14159 depending on the level of accuracy required This would give us a product of 28 26 5 The cross sectional area of the cylinder is thus 28 26 square inches Once the area is calculated the volume is found by multiplying the area by the length Figure 1 13 The result will be in cubic inches An area of 28 26 square inches multiplied by 24 inches equals a volume of 678 24 cubic inches If we want the volume measured in gallons simply divide 678 24 by the conversion factor of 231 This will yield a calculation of 2 936 gallons Using these c
4. fluid power and hydraulic systems An Overview 9 Copyright 2010 Cengage Learning All Rights Reserved May not be copied scanned or duplicated in whole or in part Due to electronic rights some third party content may be suppressed from the eBook and or eChapter s Editorial review has deemed that any suppressed content does not materially affect the overall learning experience Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it Licensed to iChapters User Copyright 2010 Cengage Learning All Rights Reserved May not be copied scanned or duplicated in whole or in part Due to electronic rights some third party content may be suppressed from the eBook and or eChapter s Editorial review has deemed that any suppressed content does not materially affect the overall learning experience Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it
5. for This Chapter n When inspecting a system remember that the hydraulic fluid may be under high pressure n When working around a system with leaks remember that hydraulic oil on the floor can be extremely slippery n Remember that when hydraulic fluid is under high pressure and when escaping under high pressure through a small leak that leak may be invisible n Remember that when hydraulic fluid is under high pressure and escaping through a small leak the escaping high pressure fluid can penetrate the skin Injected hydraulic fluid is toxic n Remember that hydraulic systems are designed to move large and heavy loads These loads can be dangerous should they move or shift unexpectedly n ALWAYS wear safety glasses Key Terms area Blaise Pascal Canadian Centre for Occupational Health and Safety force Joseph Bramah lock out and tag out noncompressible Occupational Safety and Health Administration OSHA pressure volume 1 Copyright 2010 Cengage Learning All Rights Reserved May not be copied scanned or duplicated in whole or in part Due to electronic rights some third party content may be suppressed from the eBook and or eChapter s Editorial review has deemed that any suppressed content does not materially affect the overall learning experience Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it Licensed to iChapters User I
6. ice pick can easily cause the point to penetrate tough leather This principle has been applied by humankind since prehistoric times It is the basic principle behind the stone knife Volume Area Length Area also plays a vital role in another principle Unlike in our cone example a modern hydraulic sys tem depends on the movement of flow to and through cylinders and motors through conduits hoses or pip ing Figure 1 10 All of these devices are three di mensional in nature and therefore not only have area but contain a volume Volume is the capacity of a region or of a specified container expressed in cubic units In North American measurement systems the most common measurement is gallons the same gal lons used to measure milk water and other liquids Cubic linear measurements are often used to describe volume in design and troubleshooting The most com mon unit is cubic inches in3 Similarly the most common metric measurement is liters although cubic decimeters dm3 and other length related measurements are sometimes used Imagine a cylinder with a volume of 2 gallons Since there is 231 cubic inches in a gallon we might also say there are 462 cubic inches of volume in the cylinder If the area of the surface that would be formed across the end of the circle was 12 56 inches then the length of the cylinder must be 36 78 inches A PRACTICAL APPLICATION In a more practical application let us calculate the volume
7. large end of a cone will result in what kind of pressure at the small end of the cone A A much greater pressure B A much smaller pressure C The pressure will not change D Only the force will change 1 gallon per minute 1 gallon per minute 1 gallon per minute Figure 1 14 The flow rate of fluid in any given branch of a hydraulic circuit is constant throughout the branch A restriction will cause a change in velocity of the fluid through the restriction This is similar to a river flowing through a narrow channel When the channel is wide the water in the river flows leisurely along As the channel begins to narrow the flow rate of the water will remain a constant but the speed of the water will increase in order to maintain that same flow rate This is best exemplified by the rapids that are often found at the narrow points of a river channel Anyone who has ever seen films or videos of white water rafting has seen a perfect example of this Figure 1 15 All the rules and laws of hydraulic systems and fluid power systems are at play even in this simple bottle jack The user applies a small amount of work many many times to the small piston on the side of the jack Each time the work is applied a small amount of fluid is moved from the small system to the large piston Slowly the extend side of the large piston is moved upward by each sequential movement of the small piston The pressure applied by the small piston to the
8. on mobile equipment hydraulics and therefore it is acceptable to round the 0 4893 minutes to half a minute or 30 seconds The preceding calculations assume that whatever the pump produces can arrive at the cylinder at the same rate the pump is sending it As we will see in subsequent chapters this is seldom the case The di ameter of the hoses leading to and from can limit the flow rate to the cylinder In general the smaller the diameter the lower the flow rate Decreasing the diameter causes a decrease in flow rate and as it causes this decrease in flow rate another characteristic of the fluid flow called velocity will increase As the diameter of the hose decreases the speed of a given drop of fluid must increase in order for the flow rate to be maintained Figure 1 15 This increase in speed is an increase in velocity There will be more on that in later chapters Summary Hydraulics is both an ancient science and a new technology Like any technology many complexities and nuances can affect the operation of a hydraulic system In spite of that fact all of the complexities and nuances follow a rather small number of laws and rules and are governed by a very small set of mathematical principles Understanding these principles regardless of one s skill in mathematics will make a technician efficient and skilled when troubleshooting and repair ing hydraulic systems Review Questions 1 Applying an even pressure on the
9. Licensed to iChapters User Modern Diesel Technology Mobile Equipment Hydraulics A Systems and Troubleshooting Approach Ben Watson Vice President Editorial Dave Garza Director of Learning Solutions Sandy Clark Executive Editor David Boelio Managing Editor Larry Main Senior Product Manager Sharon Chambliss Editorial Assistant Jillian Borden Vice President Marketing Jennifer Baker Executive Marketing Manager Deborah S Yarnell Marketing Specialist Mark Pierro Production Director Wendy Troeger Production Manager Mark Bernard Content Project Manager Cheri Plasse Art Director Benj Gleeksman Technology Project Manager Chrstopher Catalina Production Technology Analyst Thomas Stover c 2011 Delmar Cengage Learning ALL RIGHTS RESERVED No part of this work covered by the copyright herein may be reproduced transmitted stored or used in any form or by any means graphic electronic or mechanical including but not limited to photocopying recording scanning digitizing taping Web distribution information networks or information storage and retrieval systems except as permitted under Section 107 or 108 of the 1976 United States Copyright Act without the prior written permission of the publisher Library of Congress Control Number 2010926037 ISBN 13 978 1 4180 8043 3 ISBN 10 1 4180 8043 8 Delmar 5 Maxwell Drive Clifton Park NY 12065 2919 USA Cengage Learning products are repre
10. NTRODUCTION Modern hydraulic systems perform a wide range of jobs on mobile equipment From earthmoving to re moving trash and refuse to providing services to the disabled mobile equipment hydraulics play a vital role in a wide range of industries This book will limit itself to hydraulic system typically found in motor vehicle applications SAFETY Safety Glasses Most modern repair shops place a great deal of emphasis on eye safety When hydraulic systems suf fer a catastrophic failure such as a ruptured line and fitting they will usually do so under extreme pressure These high pressures can turn metal rubber and oil into high velocity projectiles When working on hy draulic systems safety glasses are a must Figure 1 1 If there is concern about the condition of the system especially pressure related problems a ballistic face shield in addition to the safety glasses is strongly recommended Skin Penetration Risks A rather unique though very real risk when working with hydraulic systems is that of skin penetration Ac cording to the Occupational Safety Handbook published by the Occupational Safety and Health Administra tion OSHA pressures as low as 100 psi can force oils and other fluid through the skin Figure 1 2 In addi tion to severe lacerations once these oils enter the bloodstream they often prove to be highly toxic Never Open a Pressurized Line In addition to the potential for eye damage and injecti
11. alculations if we want to move a 6 inch diameter piston within a cylinder a distance of 24 inches it would take nearly 3 gallons of fluid moving into the cylinder At this point it is easy to become overwhelmed by the math Designing a properly operating hydraulic system is a very math intensive process Although some math is required at times to get a feel for how a system should be operating troubleshooting is gener ally far less dependent on math skills Velocity Flow Rate Diameter As important as the amount of force that a hy draulic system can bring to a job is the speed at which that job can be performed This speed factor is called velocity and it is a direct function of flow rate Flow rate is a function of the capability of the pump and the diameter of the components conduits hoses and pipes carrying the fluid Figure 1 14 Flow rate is measured in gallons per minute or liters per minute Velocity is the time it takes for a mass of fluid or a hydraulic system component to move from point A to point B Velocity is usually measured in feet per second or meters per second Using our previous example of the 6 inch cylinder with a 24 inch length we will now calculate how long it will take for the piston within the cylinder to move the full range of its stroke The first thing we will need to know is the supply capacity of the pump supplying fluid to the system Let us assume that the capacity is 6 gallons per minute Knowing t
12. d to iChapters User Force Area Pressure Perhaps the most critical concept to understand in the design operation and troubleshooting of hydraulic systems is the interrelationship between force area and pressure Within Pascal s law there is a set of formulae that describe this relationship This is often referred to as the FAP or force F area A pressure P relationship F A P A F P P F A Let us say that we apply a pressure of 100 pounds per square over the surface of an object with an area of 100 square inches The force exerted on that object and therefore potentially transmitted by that object is 10 000 pounds of force Figure 1 9 Let us take this a step further Imagine applying these 100 pounds per square inch of pressure over a near cone shaped object where the surface area of one end is 100 square inches and the surface area of the other is 1 square inch The force applied to the 100 square inch surface would be 10 000 pounds If the 1 square inch surface was against another object it would be applying a force equal to the force applied to it on the larger side 10 000 pounds But since the force is spread out over an area of only 1 square inch the pressure applied by the small side to the object it is touching is 10 000 pounds per square inch Although the pressure is multiplied 100 fold the force remains the same Using this principle the force of a human hand on the handle of an awl or an
13. e that the ancient Egyptians may have used hydraulic principles in the building of many of their structures Beyond such conjecture the first patent relating to the practical use of hydraulics was issued to Joseph Bramah in 1795 Figure 1 4 In addition to hydrau lics Bramah was also granted patents on a beverage dispenser a flush toilet and a pick proof lock All of the technologies in these patents are still in use today His 1795 patent was for a simple though effective hydraulic press The operation of that press is the principle behind nearly all modern hydraulic systems In fact it could be said that today s hydraulic systems are exactly what Bramah patented in 1795 but with additional controls added to make them perform in specific ways Bramah s invention of 1795 capitalized on a theory proposed by Blaise Pascal and was in fact a refine ment of an invention by Pascal Blaise Pascal was born in 1623 and actually invented the hydraulic press that was later made practical with the addition of oil soaked leather seals by Bramah a century and a half later Pascal s most important contribution to hydrau lics was the basic operating theory This theory states that when there is an increase in pressure at any point in a confined fluid there will be an increase in pres sure at all other points in the fluid His work went on to state that when a force is applied to a piston against the confined fluid that force will create an
14. ge In a hydraulic system we think of force as the result of applying a pressure over a given area Figure 1 6 As a result the greater the area that a given pressure is applied to the greater the force In accordance with that the greater the pressure applied to a given area the greater the force The pound force or simply the pound is actually a measurement of the force required to accelerate a mass of 453 59 grams at a rate of approximately 32 17 feet per second In the metric system the equivalent to the pound is the dyne or the Newton A dyne is a centimeter gram second unit of force It is equal to the force required to accelerate a mass of one gram at a rate of one centi meter per second A Newton is the unit of force required to accelerate a mass of 1 kilogram at a rate of 1 meter per second A Newton is equivalent to 100 000 dynes Area Area is a measurement that describes the size of a two dimensional face of a solid object Area is cal culated as a measurement of length squared In most hydraulics used in North America the measurement used to describe a surface area is square inches This book will also include metric measurements The common metric measurement for area is square cen timeters Figure 1 7 Pressure Pressure is a measurement of a force applied uniformly over a surface This measurement is de scribed in units of force per square unit of linear measurement Figure 1 8 In North American appli
15. his flow rate we can determine how long it should take to move the piston the full length of the cylinder We have already de termined that the fully extended cylinder will hold 6 inch cylinder Figure 1 11 When documentation of a fluid power system refers to a 6 inch cylinder this means that the diameter of the cylinder is 6 inches r2 Area Figure 1 12 The surface area of the piston is equal to half the diameter also known as the radius times itself in other words squared times pi p r2 Area r2 Area Length Figure 1 13 Multiplying the surface area of the piston times the length of the stroke will yield the volume of the cylinder An Overview 7 Copyright 2010 Cengage Learning All Rights Reserved May not be copied scanned or duplicated in whole or in part Due to electronic rights some third party content may be suppressed from the eBook and or eChapter s Editorial review has deemed that any suppressed content does not materially affect the overall learning experience Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it Licensed to iChapters User 2 936 gallons Dividing the extended cylinder volume by the 6 gallon per minute flow rate would yield a result of 0 4893 minutes or about 29 36 seconds Al though sometimes manufacturing machinery times must be calculated and monitored that accurately this book concentrates
16. increase force B Tends to decrease force C Tends to decrease pressure psi D Both A and C 6 In the United States the agency responsible for establishing guidelines related to employee safety is A United States Safety Department B Office of Management and Safety C Occupational Safety and Health Administration D No such agency exists 7 When a submarine submerges the water applies a pressure around the cylinder of the submarine that is A Equal at all points around the cylinder B Greater on the top than it is the bottom C No pressure is applied there is only force D The force is equal but the pressure changes along the length of the cylinder 8 The lock out tag out procedure is important A To protect the technician from personal injury B To protect the equipment from damage C Both of the above D Neither of the above 9 Personal protective equipment PPE is extremely important in providing a safe working environment for the technician Who is responsible for ensuring that every technician properly wears protective equipment A The individual technician B The technician s employer C The technician s co workers D All of the above 10 A simple hydraulic bottle jack follows all the rules of fluid power and hydraulic systems except for A Flow area pressure B Area pressure velocity C Flow velocity area D It follows all the rules of
17. increase in pressure within the confined fluid That pressure change will then act upon another piston with the same change in pressure The amount of force applied to that second piston by the change in pressure will be proportional to the size of the second piston relative to the first Double the surface area of the second piston with respect to the first and the amount of force is doubled Basic Principles NATURE OF HYDRAULICS The term hydraulics derives from a Greek word that relates to water Water and other fluids have several consistent characteristics foremost among these in the technology of hydraulics is their noncompressible nature It is the nature of liquids to maintain their volume even as pressure is increased upon them Without this characteristic a ship sitting on the sea would compress the water below it the water would give way and the ship would slip to the bottom of the sea As it is the water pushes back as the ship pushes down and the offsetting forces are achieved Figure 1 5 Modern hydraulics takes ad vantage of these offsetting forces so that relatively small machines can accomplish relatively large tasks The noncompressibility of liquids makes them perfect for the immediate transmission of energy from one place to another In a closed system applying a force or setting the fluid in motion produces an im mediate and equal response at all other points in the closed system A related tech
18. large piston is multiplied in force by the surface area of the large piston allowing the bottle jack to move or lift very heavy loads 8 Chapter 1 Copyright 2010 Cengage Learning All Rights Reserved May not be copied scanned or duplicated in whole or in part Due to electronic rights some third party content may be suppressed from the eBook and or eChapter s Editorial review has deemed that any suppressed content does not materially affect the overall learning experience Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it Licensed to iChapters User 2 When fluid flows into a cylinder as the flow rate increases the speed of the piston in the cylinder A Increases B Decreases C Is unaffected D Whether it increases or decreases depends on the diameter of the cylinder 3 A pressure of 200 psi is applied to one end of a piston that has a surface area of 10 square inches What is the total force on the piston A 20 pounds of force B 200 pounds of force C 2 000 pounds of force D This cannot be calculated with the information provided 4 In the preceding question if the other end of the piston has a surface area of 100 square inches what would be the pressure on this larger end A 2 000 psi B 200 psi C 20 psi D 2 psi 5 If all other factors remain the same increasing the surface area of a piston A Tends to
19. ll learning experience Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it Licensed to iChapters User This will protect service technicians and property from damage Lock Out Tag Out Procedures There are usually formal procedures for lock out tag out outlined in company employee manuals or company safety manuals Certain basic procedures always apply Figure 1 3 Before working on repairing adjusting or re placing machinery and equipment the following pro cedures will be utilized to place the machinery and equipment in a neutral or zero mechanical state n Notify all affected employees that the machin ery equipment or system will be out of service n If the machinery equipment or system is in operation shut it down n Move switch or panel arms to Off or Open positions and close all valves or other energy isolating devices so that the energy source s hydraulic pump etc is disconnected or iso lated from the machinery or equipment Accu mulators lines hoses and all other components should be relieved of their stored pressure n Lock out and tag out all energy devices by using hasps chains and valve covers with an assigned individual lock n After ensuring that no employee will be placed in danger test all lock out and tag out processes by following the normal start up procedures n Machinery or equipment is n
20. nology pneumatics is governed by a very similar set of laws and formulae Figure 1 4 In 1795 Joseph Bramah patented a hydraulic press that worked much like the example illustrated here A small piston with a small amount of fluid moved a large piston multiplying the force many times His original press was used by the King of England in the Tower of London to flatten paper Figure 1 5 The principles of hydraulics have been known for thousands of years The basic principle can be applied to a boat or ship simply sitting in water where the weight of the ship applies a force against the water and the water applies an equal force against the ship The end result is offsetting forces combine to keep the ship to afloat 4 Chapter 1 Copyright 2010 Cengage Learning All Rights Reserved May not be copied scanned or duplicated in whole or in part Due to electronic rights some third party content may be suppressed from the eBook and or eChapter s Editorial review has deemed that any suppressed content does not materially affect the overall learning experience Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it Licensed to iChapters User but the springy nature of the pressure medium air significantly slows the response felt at all other points in a closed system SOME DEFINITIONS Force Force is the ability to do work or cause a physical chan
21. of a 6 inch cylinder with a 24 inch stroke Area Pressure Figure 1 9 The amount of force applied to a surface is equal to the amount of pressure times the amount of area the pressure is being applied over A pressure of 1 000 psi applied over a surface area of 1 000 square inches equals 1 000 000 pounds of force Length Figure 1 10 The size of the cylinder being used by an object or to actuate a device will impact the speed at which the device can operate Volume is a measure ment of the cylinder that has a direct impact on the speed of operation Volume is calculated by multi plying the surface area times the stroke or length of movement of the piston times the surface area of the system If the surface area is 10 square inches and the length of the stroke is 15 inches then the volume required to stroke the piston from full retraction to full extension is 150 cubic inches 6 Chapter 1 Copyright 2010 Cengage Learning All Rights Reserved May not be copied scanned or duplicated in whole or in part Due to electronic rights some third party content may be suppressed from the eBook and or eChapter s Editorial review has deemed that any suppressed content does not materially affect the overall learning experience Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it Licensed to iChapters User When a cylinder is referred to as a 6 inch cylinder
22. om this text or product submit all requests online at cengage com permissions Further permissions questions can be e mailed to permissionrequest cengage com Printed in the United States of America 1 2 3 4 5 XX 12 11 10 Copyright 2010 Cengage Learning All Rights Reserved May not be copied scanned or duplicated in whole or in part Due to electronic rights some third party content may be suppressed from the eBook and or eChapter s Editorial review has deemed that any suppressed content does not materially affect the overall learning experience Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it Licensed to iChapters User CHAPTER 1 An Overview Learning Objectives Upon completion and review of this chapter the student should be able to n Describe fluid flow through a typical cylinder based hydraulic system n Describe fluid flow through a typical motor based hydraulic system n Predict how pressure changes as fluid flows through a typical hydraulic system n Predict how temperature changes as fluid flows through a typical hydraulic system n Predict which components in a typical hydraulic system can affect flow n Predict where and how velocity will change in a typical hydraulic system n Describe how changes in pressure cause changes in force n Describe how changes in flow rate cause changes in the speed of operation in a system Cautions
23. on through the skin a pressurized line may be all that is supporting a major component on a vehicle or mobile hydraulic system that is being repaired As a personal anecdote I once arrived to do a class at a city owned repair shop in California Only minutes before a technician had removed a pressurized line from the cylinder on a dump truck bed The dump truck bed was elevated at the time The check valve he had assumed would hold the dump bed in the raised position was apparently defective The dump bed rapidly came down and crushed him Although he lived he was severely injured Never remove a pressurized line or a component from a pressurized line pump motor cylinder or any other component LOCK OUT TAG OUT The purpose of a lock out tag out program is to prevent the accidental operation or start up of equip ment while it is being diagnosed repaired or serviced A B C Figure 1 1 Everyone gets only a single pair of eyes Since accidents and unexpected flying parts can occur at any time while servicing fluid power systems safety glasses should be worn even when performing minor repairs or service 2 Chapter 1 Copyright 2010 Cengage Learning All Rights Reserved May not be copied scanned or duplicated in whole or in part Due to electronic rights some third party content may be suppressed from the eBook and or eChapter s Editorial review has deemed that any suppressed content does not materially affect the overa
24. ow locked out and tagged out n Should the shift change before the machinery or equipment can be restored to service the lock out and tag out must remain If the task is re assigned to the next shift those employees must perform a review of the lock out tag out pro cedure with the previous technician before being allowed to transfer their lock key and tag CAUTION After testing place the controls back in the neutral position Restoring Machinery and Equipment to Service When the task is complete and the machinery equipment or process are ready for testing or returned to normal service n Check the area to ensure that no employee is exposed to a hazard n Account for all tools repair or replace any de fects and replace all safety guards n Remove lock and tag Restore energy sources Test to ensure task has been completed satisfactorily Procedures Involving More Than One Technician In the preceding steps if more than one technician is assigned to a task requiring a lock out and tag out Small Business Safety and Health Management Series OSHA 2209 02R 2005 Figure 1 2 The Occupational Safety and Health Administration and the Canadian Centre for Occu pational Health and Safety provide detailed guide lines and procedures to ensure the safety of workers Procedures and processes are outlined and detailed in various publications of these agencies DANGER EQUIPMENT LOCKED OUT TECHNICIAN DATE
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