| Troubleshooting a pneumatic system has been | | | | Along with schematics supplied by the manufacturer, |
| considered an art, a science, or just hit-or-miss luck. | | | | another set of documents, the service/maintenance |
| In the minds of maintenance personnel, production | | | | manual and its service bulletin updates, may be |
| managers, and plant managers, the word | | | | available to assist in the diagnosis and repair of the |
| troubleshooting conjures up images of hours of | | | | machine. These may contain information about the |
| downtime and lost production. | | | | problem that has occurred. |
| However, when reduced to its basic elements, | | | | Operate the machine |
| troubleshooting a pneumatic system is a step-by-step | | | | After becoming familiar with the components and |
| procedure. Using this process can speed up the ability | | | | operation of the pneumatic system, start the |
| to determine what the problem is, the probable | | | | machine and operate it to get a first-hand view of |
| cause of the malfunction or failure, and a solution. | | | | the malfunction. See if the malfunction that has been |
| Every pneumatic circuit has a logical sequence of | | | | reported occurs again. While operating the machine, |
| operation that can involve timing logic, pressure | | | | perform a visual inspection. |
| sensing, position sensing, and speed regulation. | | | | Some questions to ask during the inspection: |
| Troubleshooting is initiated when the circuit does not | | | | Is there any excessive air leakage? |
| operate properly. | | | | Are system pressures at the levels specified on the |
| Certain general diagnostic and testing steps can be | | | | schematic or in the maintenance manual? |
| applied to any troubleshooting problem, whether the | | | | If there are manual controls for the machine, do they |
| problem occurred at startup of a new system or at | | | | feel stiff or loose in their operation? |
| a breakdown of an existing system. | | | | Are components that move, moving smoothly or |
| Think safety first | | | | erratically? |
| Safety should always be a prime concern of | | | | By operating the machine, any abnormalities may |
| maintenance personal. Compressed air is a volatile | | | | become obvious, shortening troubleshooting time. |
| element in a pneumatic circuit. Air receiver tanks have | | | | Recheck all services |
| exploded, causing severe injury to personnel and | | | | Before attempting repair on the machine after it has |
| damage to property. It is imperative to relieve | | | | been operated, once again check to see if power |
| pressure in a receiver tank prior to making any | | | | supplied to the machine has been turned off. Check |
| repairs. | | | | to see if any stored pressure remains in the system, |
| Air is also highly compressible, which is another reason | | | | because this stored pressure can cause premature |
| to be cautious in the approach to troubleshooting a | | | | actuation of the system's actuators and cause injury |
| pneumatic system. When working with overhead | | | | to personnel and damage to the machine. |
| loads that are supported by cylinders, but not | | | | Isolate subsystems |
| mechanically locked into position, block the load | | | | A malfunction in one part of the machine can be |
| before servicing the system to prevent falling or | | | | caused by a malfunction in a different subsystem on |
| drifting. | | | | the machine. Isolating the subsystems, can help focus |
| Many pneumatic systems are controlled by electrical | | | | on one system at a time. Narrowing the diagnostic |
| or electronic devices. Before attempting service or | | | | area by isolation of subsystems requires extra |
| repair on these components, be sure the electrical | | | | precaution while operating the machine. |
| power supply has been turned off. | | | | Any lines that have been disconnected and any ports |
| Pneumatic directional control valves that use electrical | | | | that have been opened should be plugged properly |
| solenoids to operate the valve spool are often | | | | to prevent unnecessary air leakage and the entrance |
| equipped with manual overrides (Fig. 1) that can be | | | | of contaminants. |
| used during troubleshooting to operate the system. | | | | While operating the machine, a close watch should be |
| Pneumatic lockout valves (Fig. 2) are excellent safety | | | | kept on the pressures within the system, so |
| devices that, when used properly on pneumatic | | | | maximum allowable pressures are not exceeded. |
| systems, can prevent accidental operation. Ensuring a | | | | Caution and safety are the two keys to this |
| safe condition should always be the first step in | | | | diagnostic step. |
| troubleshooting pneumatic systems. | | | | Make a list |
| Ask the three Ws | | | | During the previous step, the immediate problem may |
| When a breakdown in the system occurs, the | | | | be quite obvious. However, in troubleshooting, the |
| pressures of downtime loom large in the minds of all | | | | obvious may not be the root cause. |
| concerned. Before beginning repair of a system, stop | | | | As an example, the obvious problem may be slow |
| and ask these three questions: | | | | actuator speed but the root cause of the problem |
| What is or is not occurring in the system's operation? | | | | could be insufficient lubrication, no lubrication due to a |
| When did the problem begin? Was it a sudden failure | | | | faulty lubricator (Fig. 4), or bad seals within the |
| or a gradual failure? | | | | directional control valve that controls the actuator. |
| Where in the machine cycle does the problem occur? | | | | After making a list of possible causes, check those |
| Was it at startup or after the system has been | | | | items on the list and eliminate them without going |
| operating for a while? | | | | back over ground previously covered. This list will also |
| What is or is not occurring in the system can often | | | | reduce the time required for troubleshooting and can |
| be answered by the system operator. Answers to | | | | eliminate the parts exchanging syndrome that often |
| questions such as slow actuator speed or inability of | | | | accompanies troubleshooting. |
| the actuator to move could lead to looking for a low | | | | The example of slow actuator speed shows why a |
| flow rate or low pressure. | | | | thorough understanding of component and system |
| Asking, "When did the problem begin?' can often lead | | | | operating principles is required to accurately match |
| to troubleshooting steps looking for worn | | | | the problem to the cause. |
| components or leaks. Sudden malfunctions can point | | | | After making a list and narrowing the possible causes, |
| to breaks and possible mechanical problems, ruptures | | | | it is now time to make a decision on which one of |
| in lines, or other catastrophic failures. By determining | | | | the remaining causes is most likely to be the reason |
| the when, the problem search can be narrowed in its | | | | for the malfunction. Reaching this conclusion may, at |
| scope. | | | | first, appear difficult but this step is essentially the |
| Asking, "Where in the machine cycle does the | | | | starting point for the repair portion of |
| problem occur?" can reveal a reoccurring condition. | | | | troubleshooting. Up to now the system has been |
| If good maintenance records have been kept, | | | | evaluated, now it is time to test the conclusion. |
| reoccurring problems should have been recorded. This | | | | In the example, testing the conclusion may be merely |
| information makes the troubleshooting process much | | | | the need to add lubricant to the lubricator or make |
| easier. | | | | an adjustment to the drip rate of the lubricator. |
| A maintenance person who stops and asks the three | | | | Conducting various tests such as pressure checks |
| Ws can reduce downtime by not having to guess at | | | | with an accurate gauge, checking actuator alignment, |
| what is wrong. However, if these questions do not | | | | checking flow rate in the system with a flow meter, |
| yield a satisfactory diagnosis the maintenance person | | | | or temperature checking of the air system, can |
| must begin the mechanics of troubleshooting by | | | | further reduce the number of causes remaining on |
| visually inspecting the machine. | | | | the list and accurately pinpoint the cause. |
| Make a visual inspection | | | | Repair or replace |
| Walking around the machine will often uncover | | | | Testing the conclusion automatically leads to deciding |
| problems such as worn or burst hoses, loose | | | | whether to repair or replace a component. Many |
| components, and broken components. This is the | | | | factors can influence this step. Repairing parts |
| time to become familiar with the components | | | | immediately for reinstallation on the machine increases |
| contained in the pneumatic system. | | | | downtime, and the cost factor of this downtime is a |
| If unfamiliar with the components, or if unfamiliar with | | | | significant consideration. |
| the machine operation, ask as many pertinent | | | | To simply replace the part with a new or rebuilt |
| questions about the system as possible. Before trying | | | | component would reduce the amount of downtime; |
| to operate the system or attempt repairs, | | | | however, the question of inventory cost now |
| understand the interrelations of all the components | | | | becomes a factor. |
| and the sub-systems found on the machine. | | | | Another point that may influence the repair-or-replace |
| Read the schematics | | | | question is component availability. Obviously if the |
| Every pneumatic system should have two forms of | | | | component is not readily available, then repairing may |
| documentation that will assist in troubleshooting. One | | | | be the only alternative. Still another aspect may be |
| document is a schematic drawing of the pneumatic | | | | the inhouse capability to make repairs. |
| circuit (Fig. 3). The schematic is a road map. It not | | | | After the malfunction has been corrected, one final |
| only explains the operating function of the | | | | step remains, the need to report the findings. |
| components but also is a valuable diagnostic tool. | | | | Report what you did |
| The schematic contains useful information about | | | | Paperwork is often neglected, but in the case of |
| pressure test point locations; pressure settings of | | | | pneumatic troubleshooting it is a vital part of the |
| regulators and other pressure valves; flow rates | | | | procedure. This paperwork helps to maintain a record |
| within the system; cylinder stroke lengths, and air | | | | of changes, problems, and solutions that have |
| motor speeds as well as a bill of materials for the | | | | occurred to individual machines. Schematic updates |
| system. This type of information can aid in | | | | are necessary to keep this diagnostic tool current |
| determining if the system is operating within its | | | | and accurate. Report making also serves as a good |
| design parameters. | | | | reference should any problems reoccur in the future. |