Abstract:
Method, apparatus and computer program product are provided for controlling desiccant regeneration in air dryer equipment for a railroad locomotive. The method allows calculating an amount of air conditioned by the air dryer equipment over a period of time. The method further allows storing predefined criteria for initiating desiccant regeneration in the air dryer equipment. The calculated amount of air conditioned by the air dryer equipment is correlated relative to the predefined criteria, and upon the calculated amount of air conditioned by the air dryer equipment meeting the predefined criteria, desiccant regeneration is initiated in the air dryer equipment.

Description:
[0001]     This application claims the benefit of U.S. Application Ser. No. 60/581,063 which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     It is known to use multi-cylinder air compressors on freight and passenger locomotives to supply compressed air to various locomotive systems, such as the operating and control equipment of a railway air brake system. Prior art techniques for servicing the air compressor system have essentially required uninstalling and shipping major components of the air compressor system, such as the entire compressor, to a specialized compressor servicing site. This approach may lead to unnecessary costs and delays, if the type of component causing the malfunction was one that could be replaced in-situ at the locomotive (i.e., as installed onboard the locomotive) without having to incur the delays and expenses associated with shipping the entire compressor to the specialized servicing site. However, heretofore there was no effective procedure or test apparatus to diagnose locomotive air compressors in-situ to determine if the malfunction was due to an in-situ serviceable component or to a cause that required removal of the air compressor system and servicing off-board of the locomotive. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0003]     The features and advantages of the present invention will become apparent from the following detailed description of the invention when read with the accompanying drawings in which:  
         [0004]      FIG. 1  illustrates a schematic representation of an exemplary locomotive air compressor system that benefits from aspects of the present invention; and  
         [0005]      FIG. 2  is made up of  FIGS. 2A-2C  that collectively depicts a flow chart that illustrates an exemplary sequence of tests that may be performed on the air compressor system of  FIG. 1  for identifying malfunctioning components while the system remains onboard the locomotive.  
         [0006]      FIG. 3  is a schematic representation of one exemplary embodiment of air dryer equipment, as may be configured for performing a condition-based desiccant regeneration process in lieu of regenerating at a fixed time interval. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0007]     The inventor of the present invention has innovatively recognized a sequence of diagnostics techniques that may be performed in-situ onboard a locomotive for identifying in a locomotive air compressor system (out of various components that make up such a system) a specific malfunctioning component that is likely to require a servicing action and further identifying a type of servicing action appropriate for correcting the malfunction. This type of technique is particularly advantageous in the locomotive industry since now one may be able to replace certain identified components in-situ on the locomotive while at a generic or non-specialized locomotive service shop without having to uninstall and ship main components of the compressor system for servicing at a specialized suppliers site. This is a significant improvement over prior art techniques that have essentially required uninstalling and shipping major components of the air compressor system, such as the compressor, regardless of whether in fact there is ultimately determined to be a need for such specialized servicing. For example, a cylinder head including intake and outlet valves could be replaced at the generic service shop without having to uninstall and ship the entire compressor to the specialized suppliers site. Below is a description of an exemplary compressor air system that may benefit from the diagnostics techniques embodying aspects of the present invention.  
         [0008]     FIG. 1  shows an air compressor system  10 , including a pair of intercoolers  12  and  14 , an aftercooler  16 , a main storage reservoir  18 , and associated piping. In one exemplary embodiment air compressor system  10  comprises a multi-cylinder, two-stage, air-cooled compressor having a first low pressure cylinder  20  and a second low pressure cylinder  22  and a high pressure cylinder  24 , each of which may be provided with cooling fins. As shown, the pair of low pressure cylinders  20  and  22  and the high pressure cylinder  24  may be mounted on and supported by a crankcase  26  in the usual manner and include respective pistons which are actuated by connecting rods driven by a rotatable crankshaft  28 . In one exemplary embodiment the crankcase  26  includes a breather valve  27  and an oil-fill plug  29 . One end of the crankshaft  28  may be coupled to and driven by a suitable rotatable prime mover, such as an electric motor  17  or the like, while the other end of the crankshaft  28  may be attached to a rotary cooling fan assembly (not shown). Crankcase seals  21  and  23  are commonly employed to seal both ends of the crankshaft  28  to prevent leakage of lubricating fluid. One or more side removable covers  25  may be provided to provide access to the interior of the crankcase  26 .  
         [0009]     An inlet valve  30  of the low-pressure cylinder  20  is connected by conduit  32  to an intake filter  34 , while an inlet valve  36  of the low-pressure cylinder  22  is connected by conduit  37  to an air intake filter  38 . An outlet valve  40  of the low-pressure cylinder  20  is connected to an inlet header of the first intercooler  12  via a pipe  42 . It will be appreciated that although  FIG. 1  illustrates just one inlet and outlet valve per cylinder head assembly, in one exemplary embodiment, each cylinder head assembly may comprise a pair of inlet and outlet valves per cylinder head. Typically, the valves may be spring-loaded valves responsive to negative or positive pressure to reach either a closed or an open condition.  
         [0010]     An outlet header of intercooler  12  is connected to one inlet of a T-pipe fitting  44 . Similarly, an outlet valve  46  of the low pressure cylinder  22  is connected to an inlet header of the second intercooler  14  via a pipe  48 . An outlet header of intercooler  14  is connected to the other inlet of the T-pipe fitting  44 , while the outlet of the T-pipe fitting  44  is connected to an inlet valve  50  of the high pressure cylinder  24 . An outlet valve  52  of high pressure cylinder  24  is connected by suitable conduits and fittings forming piping  54  to an inlet header of the aftercooler  16 . An outlet header of aftercooler  16  is connected by suitable conduits and fittings forming piping  56  to the inlet of the main storage reservoir  18 .  
         [0011]     Below is a description of an exemplary sequence of tests for identifying in a locomotive air compressor system any of various components that are likely to require a servicing action that, for example may performed in-situ onboard the locomotive or at an specialized compressor servicing site based on the results of the performed test sequence.  
         [0000]     Crankcase Inspection Test:  
         [0012]     Evacuate oil from crankcase and then remove side covers  25  and inspect the interior of the crankcase  26 , e.g., bearings and lubrication system. For example, if one detects the presence of pieces of metal, or bad bearings, then a servicing decision would be to remove the compressor for an overhaul. If this upfront test is passed, one would reattach the side covers  25  and continue with the tests below.  
         [0013]     Intercoolers and Low Pressure Cylinder Tests:  
         [0000]     Test 1A (Pressurizing Intercoolers and One of the Two Low Pressure Cylinders):  
         [0014]     1. Remove air filters  34  and  38 .  
         [0015]     2. Remove oil-fill plug  29   
         [0016]     3. Block breather valve  27   
         [0017]     4. Block one of the intake conduits (e.g., the conduit  32  that provides an intake to one of the low pressure cylinders, e.g., low pressure cylinder  20 ).  
         [0018]     5. Block the pipe that provides a discharge outlet to the aftercooler  16 . That is, block pipe  56 .  
         [0019]     6. Install on the other intake conduit (e.g., conduit  37  that provides an intake to low pressure cylinder  22 ), a pressurizing fixture (e.g., including a pressure gage and valve).  
         [0020]     7. Pressurize to a predefined pressure (e.g., 60 psi) and start to measure time, e.g., start a timer.  
         [0021]     8. Record time elapsed upon reaching one or more predefined pressure levels, e.g., 55, 50, 45 and 40 psi pressure.  
         [0022]     9. Compare the actual elapsed time recorded at the predefined pressure levels relative to predefined threshold times.  
         [0023]     10. Check for possible air leak through intercoolers  12  and  14 , e.g., visual check.  
         [0024]      11 . Check for possible airflow through oil-fill opening  29 .  
         [0025]     The predefined pressure (e.g., 60 psi) applied in step  6  above is sufficiently high to cause intake valve  36  to open and pressurize the low-pressure cylinder  22  as well as intercoolers  12  and  14 . The predefined pressure is also sufficiently low to stay within the pressure ratings of the intercoolers  12  and  14  and avoid actuating the intake valve  50  of the high-pressure cylinder  22  to an open condition. At this point, presuming the outlet valve  40  is operating properly, the head of the low-pressure cylinder  20  has not been pressurized because the outlet valve  40  is in a closed condition in response to the applied pressure. Thus, one would perform another sequence of steps for pressurizing the head of the low-pressure cylinder  20 . More specifically,  
         [0000]     Test 1B (Pressurizing Intercoolers and the Other One of Low Pressure Cylinders):  
         [0026]     1. Block the other one of the intake conduits (e.g., conduit  37 ) that provides an intake to low-pressure cylinder  22 ).  
         [0027]     2. Install on the other intake conduit (e.g., conduit  32  that provides an intake to low pressure cylinder  20 ), the pressurizing fixture  
         [0028]     3. Pressurize to the predefined pressure (e.g., 60 psi) and start to measure time, e.g., start a timer.  
         [0029]     4. Record time elapsed time upon reaching one or more predefined pressure levels, e.g., 55, 50, 45 and 40 psi pressure.  
         [0030]     5. Compare the actual elapsed time recorded at the predefined pressure levels relative to predefined threshold times.  
         [0031]     6. Check for possible air leak through intercooler  12  and  14 , e.g., visual check  
         [0032]     7. Check for possible airflow through oil-fill opening.  
         [0033]     The foregoing sequence is essentially arranged for determining whether there is a leak in any (or both) of the intercoolers  12  and  14  and whether there is a leak in any of the low-pressure cylinder heads, such as air leaking by the piston rings of any of the low-pressure cylinder heads and into the crankcase. The inventor of the present invention has identified failure mode indications associated with respective components of the compressor system that may be observed during the test sequence. One key advantage of the present invention over prior art techniques is being able to accurately distinguish and identify the type of failure modes that may be corrected in-situ from those that will require removal of major equipment from the locomotive for servicing at the specialized servicing site. Occurrence of specific indications would point out to a likely malfunction in a given component. For example, intercooler leaks may be generally characterized as relatively slow leaks compared to a low-pressure cylinder wall leak. The presence of intercooler leaks may be determined by visual inspection and/or a relatively moderate depressurizing rate (e.g., if the elapsed time to reach 40 psi is approximately 15 seconds, this may be indicative of an intercooler leak). Intercooler leaks tend to be visually detectable since intercoolers that have been in operational use for some time tend to collect visually detectable debris in their interior.  
         [0034]     In the event of a low-pressure cylinder wall leak, e.g., air passes into the crankcase from a respective one of the low-pressure cylinder heads, then one may be able to detect airflow through the oil-fill opening. This detection may be accomplished by monitoring the condition of a tape or other suitable thin flexible member placed over the oil-fill opening. In addition, service personnel may feel or hear such airflow. Moreover, a low-pressure cylinder wall leak tends to exhibit a higher depressurizing rate as compared to an intercooler leak. For example, while an intercooler leak may take about 15 seconds to reach 40 psi, a low-pressure cylinder wall leak may take just 5 seconds or less to reach 40 psi. The ability to determine the presence of an intercooler failure versus a cylinder wall failure is significant since the intercoolers may be readily replaced at the locomotive without having to remove the entire compressor whereas a cylinder leak into the crankcase typically requires removal of the entire compressor for an appropriate overhaul at a specialized service site.  
         [0035]     It has been observed from test data that variation in the recorded elapsed times (indicative of different depressurizing rates) obtained during Tests 1A and 1B tend to indicate that the intercoolers  12  and  14  are functioning properly and that the cause of this variation is likely to be caused by some other malfunctioning component, but not the intercoolers. This follows since during Tests 1A and 1B both intercoolers represent an assembly tested in common during each test and thus variations that may arise in the recorded elapsed times would tend to point to a different failure mode, such as leakage in one of the low-pressure cylinder walls.  
         [0000]     Test 2—Aftercooler and High Pressure Cylinder Tests:  
         [0036]     1. Open intake conduits to low-pressure cylinders  20  and  22 .  
         [0037]     2. Install pressurizing fixture at aftercooler discharge outlet. That is, pipe  56 .  
         [0038]     3. Pressurize to a predefined pressure, e.g., 80 psi and start to measure time, e.g., start a timer.  
         [0039]     4. Record time elapsed upon reaching one or more predefined pressure levels, e.g., at 75, 70, 65 and 60 psi.  
         [0040]     5. Compare the actual elapsed time recorded at the predefined pressure levels relative to predefined threshold times.  
         [0041]     6. Check for possible air leak through aftercooler  16 , e.g., visual check  
         [0042]     7. Check for possible airflow through oil-fill opening.  
         [0043]     One aspect of this test allows pressurizing the aftercooler  16  and determining the presence of a leak in the aftercooler. The presence of such a leak may be determined by visual inspection and/or a relatively moderate depressurizing rate (e.g., if the elapsed time to reach 60 psi is approximately 15 seconds, this may be indicative of an aftercooler leak. Another aspect of this test also allows determining a malfunction in the outlet valve  52  of the high-pressure cylinder  24 . For example, if the outlet valve  52  is operating properly, then when the aftercooler  16  is pressurized through pipe  56 , that valve should remain closed and the pressurization should be limited to the aftercooler  16 . In the event of a leaky outlet valve  52  in the high-pressure cylinder, the head of the high-pressure cylinder will also become pressurized. Test data reveals that once a leaky valve has been found in a given cylinder head, there tends to be a likelihood that the remaining valves associated with that cylinder head will also require replacement. Thus, assuming the outlet valve  52  of the high-pressure cylinder is found to be leaky, one would replace the cylinder head for that cylinder. This is a relatively straightforward servicing operation that may be performed without removing the entire compressor from the locomotive. As described in the context of Tests 1A and 1B, monitoring whether there is airflow through the oil-fill port may point to a leak in the high-pressure cylinder head, such as air leaking by the respective high-pressure piston rings and into the crankcase. Once again being able to determine different failure modes is significant since different course of actions will be taken depending on the specific malfunction or failure mode that has been identified. For example, replacement of the aftercooler  16  and/or the high-pressure cylinder head including the respective intake and outlet valves  50  and  52  may be performed at the locomotive whereas a cylinder leak into the crankcase will require removal and shipping of the compressor for overhaul at a specialized compressor service site.  
         [0000]     Test 3—(Crankcase Pressure Test):  
         [0044]     1. Remove test fixture from aftercooler discharge outlet.  
         [0045]     2. Install pressurizing fixture at oil fill port.  
         [0046]     3. Pressurize to a predefined pressure, e.g., 10 psi, and start to measure time, e.g., start a timer.  
         [0047]     4. Compare the actual elapsed time recorded at the predefined pressure levels relative to one or more predefined threshold times, e.g., at 9, 8, 7, 6, 5, 4, 3 and 2 psi pressure.  
         [0048]     This test primarily allows determining the health of the crankcase seals  21  and  23 . In one exemplary embodiment, with the motor  17  installed, physical access to the end of the crankshaft where seal  23  is situated is not realizable. Thus, by pressurizing the crankcase and monitoring a depressurization rate and comparing to a predefined threshold, (e.g., if the elapsed time to reach 2 psi is approximately 60 seconds), one may obtain an indication of crankcase seal health without having to remove the compressor motor.  
         [0049]     Referring back to  FIG. 1 , air dryer equipment  60  may be connected to remove moisture and/or other particulates, such as oil particulates, that may be present in the compressed air to avoid condensation and/or contamination on the surfaces of one or more locomotive equipment (not shown) situated downstream that receive the pressurized air. In one known exemplary embodiment, the dryer equipment may comprise adsorbent-type air dryer that uses a regenerative desiccant that adsorbs moisture, at least up to a certain level of adsorption capacity. The moisture accumulated by the desiccant is then removed via a stream of dried air redirected through the desiccant to purge the moisture into the atmosphere. In one known technique, the air dryer equipment is responsive to a timer signal so that the regeneration process is performed at a fixed interval, (e.g., approximately every 2 minutes) regardless of actual usage of compressed air by the equipment downstream. This known technique forces the air compressor system to turn on and off based on the fixed timing for regeneration regardless of the actual consumption of compressed air by the locomotive equipment downstream.  
         [0050]     In one exemplary embodiment of a system in accordance with aspects of the present invention, a flowmeter  62  may be coupled to provide a signal indicative of the flow rate and/or pressure changes of the compressed air passing therethrough to a controller  64 . The flow rate may be mathematically integrated over a period of time to calculate the actual volume of compressed air passing through the flowmeter  62 . A memory or look-up table  66  may be used to compare the volume of compressed air actually used relative to a predefined volume for performing the regeneration process, as may be based on the adsorption capacity of the desiccant. Once the volume of compressed air actually used equals or exceeds the predefined volume for performing regeneration, a regeneration signal would be sent by controller  64  to the dryer equipment to perform the regeneration process. That is, in lieu of regenerating at a fixed time interval, one commences the regeneration process using a condition-based regeneration technique, such as may based on the actual utilization of pressurized air, as may be actually utilized by the equipment downstream supplied by the air compressor system.  
         [0051]      FIG. 3  is a schematic representation of one exemplary embodiment of air dryer equipment  60 , as may be configured for performing a condition-based desiccant regeneration process in lieu of solely regenerating at a fixed time interval. The description that follows will provide a brief operational overview of air dryer equipment  60 . Furthermore, details will be provided of a relatively low-cost and uncomplicated modification to commercially available air-drying equipment that would allow for performing a condition-based regeneration process embodying aspects of the present invention. By way of example, such a modification may be performed to air dryer model 994 purveyed by Graham-White Manufacturing Co. It will be understood that in its broad aspects, the present invention is not limited to any particular type of air dryer model and/or manufacturer.  
         [0052]     After a coalescer  300  has substantially removed bulk liquids and particulates, e.g., oil particles, from compressed air passing from reservoir  18  ( FIG. 1 ), air that flows from coalescer  300  essentially just includes water vapor. This moist air may be directed though a first set of desiccant-filled towers; let us say desiccant towers  302  and  304 , by an inlet diverter valve  306 . By way of example, air may flow in a first direction (e.g., upwards) in desiccant tower  302  and then in a second direction (e.g., downwards) in desiccant tower  304 . Air from desiccant tower  304  flows through an outlet valve  308  that passes substantially dry, oil-free and clean compressed air. This air passes through a constriction  309  in outlet tube  311  and at least a portion of this air is directed to air-driven equipment (not shown) situated downstream relative to air dryer equipment  60 . As air passes through constriction  309 , a change in pressure (Venturi effect) develops across such a constriction. The inventor of the present invention has innovatively recognized that the addition of a suitable pressure sensor  313  across constriction  309  provides one alternative embodiment for measuring the airflow rate passing through outlet tube  311 . Essentially, this embodiment may be viewed as one practical way for achieving the operational functionality of flowmeter  62  ( FIG. 1 ) without requiring costly and time-consuming equipment redesign. That is, a relatively low-cost and uncomplicated modification can be made to presently existing equipment to provide an airflow rate measurement that may be mathematically integrated by controller  64  to calculate the actual volume of compressed air passing through tube  311 .  
         [0053]     It will be appreciated that controller  64  need not be a separate controller relative to air dryer equipment  60  since the processing functions for performing a condition-based desiccant regeneration may be programmed into an embedded controller, as may be part of the air dyer equipment  60 . Once a condition-based determination is performed relative to the first set of desiccant-filled towers, the inlet diverter valve  306  is actuated to switch the flow of air through a second set of desiccant-filled towers, such as desiccant towers  310  and  312 .  
         [0054]     Although  FIG. 3  illustrates two sets of desiccant towers, wherein each set is made up of two desiccant towers or tanks, it will be appreciated that the present invention is not limited to any specific number of desiccant tanks. Generically, one may use just two desiccant tanks for drying the compressed air. For example the piping and valving may be set for delivering a flow of air to be dried to one tank, e.g., constituting a first tank, and directing a volume of air that has been dried in the first tank to the other tank, e.g., constituting a second tank. One may start regeneration of desiccant in the second tank when the calculated amount of air conditioned by the first tank meets a predefined criteria by reversing the flow of air as between the two tanks. The predefined criteria is based on the amount of air that has been conditioned by the first tank. Once desiccant in the second tank has been reconditioned, a flow of air to be dried is directed to the second tank and a volume of the dried air from the second tank is directed to the first tank to regenerate desiccant in the first tank. The above process of air drying and desiccant regeneration is repeated in alternating fashion switching from one tank to the other tank based on the amount of air that has been conditioned at any given tank, as opposed to performing regeneration based on a fixed time interval that may have little to do with the actual condition of the desiccant.  
         [0055]     Desiccant towers undergoing regeneration, let us say desiccant towers  310  and  312 , may be isolated relative to compressed air flow by inlet diverter valve  306  and outlet shuttle valve  308 . The exhaust valve  314 , which is connected to the desiccant towers undergoing regeneration (e.g., desiccant towers  310  and  312 ), may be opened to reduce to atmosphere the pressure in such desiccant towers. Some amount of dry pressurized air may pass through a self-adjusting purge valve  316 . Details regarding the operation of purge valve are well known to those skilled in the art and for the sake of not burdening the reader with minutia for purposes of the present invention such details are omitted from the present description. Suffices to say that self-adjusting purge valve  316  is responsive to the amount of air that passes through outlet tube  311 . More specifically, the more air that passes through outlet tube  311 , the more air that self-adjusting purge valve  316  passes to the desiccant towers undergoing regeneration.  
         [0056]     In one exemplary embodiment, air that passes through purge valve  316  is directed through one of a pair of purge check valves  320  and then through the desiccant towers undergoing regeneration. As dry air flows through the desiccant beads in desiccant towers  310  and  312 , this dry air flushes adsorbed water from the desiccant beads therein and discharges such air to atmosphere through open exhaust valve  314 . At the end of a regeneration cycle and prior to switching inlet diverter valve  306 , exhaust valve  314  is closed and air from self-adjusting purge valve  316  may be used to gradually repressurize the regenerated desiccant towers. Switching of diverter valve  306  and exhaust valve  314  may be performed in response to pressurizing effects caused upon applying regeneration switching signals to solenoid valves  324  and  326  by controller  64 . That is, aspects of the present invention are directed to a regeneration control strategy that is based on the actual condition of the desiccant beads, as opposed to a purely timed regeneration control strategy regardless of whether or not the desiccant has reached (or is relatively close) to moisture saturation. It is estimated that when using a condition-based regeneration process during a locomotive idling condition, the period of time for initiating a regeneration cycle may be approximately 30 minutes, as compared to performing regeneration approximately every 2 minutes under the known temporal-based regeneration control strategy. It will be appreciated that this regeneration technique substantially reduces the operational demands on air compressing system  10  ( FIG. 1 ) and is conducive to a relatively longer air compressor life as well as incremental reductions in operational and servicing costs for the compressor.  
         [0057]     The inventor of the present invention has further recognized that the flow meter  62  may be used to monitor degradation in the air compressing ability of the air compressor system. For example, the air compressor may be rated to supply a volume of compressed air within a predefined range at a predefined pressure. For example, in one exemplary embodiment, the compressor may be rated to deliver pressurized air in a range from approximately 145 cfm to approximately 180 cfm at a pressure of about 140 psi. As the air compressor ages, the ability to compress air will be gradually diminished, and it is thus desirable to determine whether the air compressor is able to pressurize air within an acceptable range. It is further contemplated that one could, based on past and present air compressing capacity, predict a future point in time when the air-compressing ability of the compressor system may be unacceptable. One may collect data from field-deployed air compressors and/or analytically or empirically derived data to extrapolate in time the present compressing ability of a given compressor to predict the point in time at which the compressing ability of the given compressor may no longer be acceptable so as to perform appropriate maintenance for that given compressor before reaching an unacceptable level of performance. For example, one may collect and store historical data from a plurality of air compressors like the one undergoing inspection to establish reference data for comparing actual data from the compressor undergoing inspection to predict the point in time when that compressor is likely to require a comprehensive servicing action, e.g., compressor overhaul. This data may be collected and stored on a suitable memory device and the data may be downloaded either during a servicing operation at a locomotive service site, or the data may be transmitted by communications equipment onboard the locomotive to a remote diagnostics center. One exemplary sequence for determining air-compressing capacity may be as follows:  
         [0000]     Air Compressing Capacity Test:  
         [0058]     1. Run air compressor for a predefined amount of time (e.g., 30 minutes) with the compressor motor at a predefined first rpm (e.g., 600 rpm).  
         [0059]     2. Hold the pressure at a predefined pressure (e.g., 140 psi).  
         [0060]     3. Monitor parameters indicative of reaching a set of predefined operational conditions, an example of such parameters may be lubrication oil temperature and oil pressure.  
         [0061]     4. Use the signal from the flowmeter  62  to calculate volume of pressurized air actually supplied by the compressor.  
         [0062]     5. Run air compressor for a predefined amount of time (e.g., 10 minutes) with the compressor motor at a second rpm (e.g., 1050 rpm) and repeat steps 2-4 above.  
         [0063]     6. Compare actual volume of pressurized air delivered by the compressor relative to a predefined air volume range indicative of whether the capacity of the compressor to deliver pressurized air is acceptable or not.  
         [0064]      FIG. 2  is a flow chart of a sequence of tests embodying aspects of the present invention for performing diagnostics of an air compressor system on board a locomotive. In one exemplary sequence, as illustrated at block  200 , one may initially perform crank case inspection to determine the health of mechanical components within the interior of the crankcase. As shown at decision diamond  202 , if the crank case inspection is not passed then, as shown at block  244 , the corrective action would be to remove the compressor from the locomotive for compressor overhaul at a specialized service site. If the crank case inspection test is passed one proceeds to block  204  to perform Test 1A, that is pressurizing the intercoolers and one of the two lower pressure cylinders. As shown at decision diamond  206 , if an intercooler leak is detected, as shown at block  208 , one proceeds to replace the leaking intercooler in-situ. To verify that the intercooler leak has been corrected, one would return to block  204  and repeat Test  1 A. As shown at decision diamond  210 , another possible failure mode that may be detected while performing Test 1A is detecting a low-pressure cylinder wall leak. If a low-pressure cylinder wall leak is detected, one proceeds through connecting node  100  to block  244  to remove the compressor from the locomotive for compressor overhaul at a specialized service site.  
         [0065]     Presuming that no intercooler leak or low pressure cylinder wall leak has been detected, one continues at block  212  to perform Test 1B. That is, pressurizing the intercoolers and the other one of the low-pressure cylinders. As shown at decision diamond  214 , if an intercooler leak is detected, as shown at block  216 , one proceeds to replace the leaking intercooler in-situ. To verify that the intercooler leak has been corrected, one would return to block  212  and repeat Test 1B. As shown at decision diamond  218 , another possible failure mode that may be detected while performing Test 1B is detecting a low-pressure cylinder wall leak. If a low-pressure cylinder wall leak is detected, one proceeds through connecting node  100  to block  244  to remove the compressor from the locomotive for compressor overhaul at a specialized service site. Presuming that no intercooler leak or low-pressure cylinder wall leak has been detected, one continues at block  220  to perform Test 2. That is, aftercooler and high-pressure cylinder test. One of the possible failure modes that may be diagnosed while performing Test 2, as shown at decision diamond  222 , is an aftercooler leak. In the event of an aftercooler leak at block  224 , one proceeds to replace the aftercooler in-situ. To verify that the aftercooler leak has been corrected, one would return to block  220  and repeat Test 2. As shown at decision diamond  226 , another possible failure mode that may be detected while performing Test 2 is a malfunctioning high-pressure valve, e.g., a malfunctioning intake high-pressure valve. If a malfunctioning high-pressure valve is detected, then one proceeds to block  228  to perform a corrective action in-situ, such as replacing the high-pressure cylinder head assembly. To verify that the high-pressure valve malfunction has been corrected one may return to block  220  to restart Test 2. As shown at decision diamond  230 , a third possible failure mode that may be detected while performing Test 2 would be to detect a high-pressure cylinder wall leak. If such a high-pressure cylinder wall leak is detected, one proceeds through connecting node  100  to block  244  to remove the compressor from the locomotive for compressor overhaul at the specialized service site.  
         [0066]     Once Test 2 has been successfully passed, one proceeds to block  232  to perform Test 3. That is, the crankcase pressurization test. As shown at decision diamond  234 , in the event no crankcase seal leak is detected, one then proceeds to block  236  to perform the air compressing capacity test. In the event a crank case seal leak is detected, one proceeds to block  238  to replace the crankcase seals. As shown at decision diamond  240 , if the air compressing capacity is determined to be within an appropriate range of volume of pressurized air this would be the end of the test sequence as shown at block  242 . If the air compressing capacity is unacceptable, then one proceeds to block  244  to remove the compressor from the locomotive for a compressor overhaul servicing.  
         [0067]     While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.