Patent Publication Number: US-8984930-B2

Title: System and method for diagnosing a reciprocating compressor

Description:
TECHNICAL FIELD 
     Embodiments of the subject matter disclosed herein relate to a system and a method for diagnosing a reciprocating compressor. 
     DISCUSSION OF ART 
     Compressor components may degrade during operation in various ways. For example, the effectiveness of valves may degrade causing leakage of charged air back into cylinders. Leaky valves can be caused by oil getting passed through the valves, recompressed, heating up to high temperatures, and carbonizing on the valves thereby causing the valves to lose efficiency and leak. The continuation of degradation of the valves results in higher temperatures, excessive component wear, and eventual valve failures which renders the compressor unable to provide charged air to a locomotive or other user of compressed air or other gas. Currently, reciprocating compressor prognostic and diagnostic methods center on vibration, acoustic, thermal or other technologies which require additional sensors beyond the basic output or reservoir pressure sensor. 
     BRIEF DESCRIPTION 
     In an embodiment, a method for a compressor is provided. The method includes diagnosing a valve leak condition of the compressor based on piston motion within the crankcase. 
     In an embodiment, a controller is used to determine a condition of a reciprocating compressor based on displacement of a piston during a time interval subsequent to a reservoir filled to a pressure level. Displacement of the piston is indicative of a valve leak within the reciprocating compressor. 
     In an embodiment, a reciprocating compressor includes at least one piston, each piston is coupled to a crankshaft and disposed within a respective cylinder. A reservoir stores charged air output by the cylinders. An exhaust valve allows air compressed by each piston to transmit from the respective cylinder to the reservoir. An intake valve allows air to enter each respective cylinder prior to displacement of the piston. A sensor measures at least one metric during a time period that is indicative of a leak condition of each exhaust valve at the final compressor stage. 
     In an embodiment, a method is employed for a reciprocating compressor operationally connected to a reservoir. The reservoir is filled to meet or exceed a pressure level. A valve disposed between the reservoir and one or more cylinders is closed, wherein each cylinder houses a piston, the piston is not in a bottom dead center position. The compressor is closed with respect to atmosphere to maintain a charged air condition within the compressor. If piston motion is detected, a signal is output to indicate that the valve has a leakage condition. 
     This brief description is provided to introduce a selection of concepts in a simplified form that are further described herein. This brief description is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference is made to the accompanying drawings in which particular embodiments and further benefits of the invention are illustrated as described in more detail in the description below, in which: 
         FIG. 1  shows an example embodiment of a vehicle including a compressor having a crankcase. 
         FIG. 2  shows a detailed view of the compressor including high and low pressure cylinders. 
         FIG. 3  shows an example embodiment of a cylinder of the compressor during the compression stroke. 
         FIG. 4  shows an example embodiment of a cylinder of the compressor during the intake stroke. 
         FIG. 5  shows an example embodiment of a method for diagnosing a condition of the compressor. 
         FIG. 6  shows an example embodiment of a method for responding to a condition of the compressor. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the subject matter disclosed herein relate to systems and methods for diagnosing a compressor. The compressor may be included in a vehicle, such as a locomotive system. Other suitable types of vehicles may include on-highway vehicles, off-highway vehicles, mining equipment, and marine vessels. Other embodiments may be used for stationary compressors. These vehicles may include a compressor with components that degrade with use. Such condition can be detected to identify a faulty condition and initiate preemptive remedial action in response to prevent overall compressor failure. 
     The subject embodiments are intended to detect leaks in the valves of an air compressor, such as a reciprocating compressor, by evaluating the crank position or speed of the compressor (high pressure exhaust valve in particular). Once the compressor has charged the reservoir to an acceptable limit, the compressor shuts off. This technology focuses on the speed signal (e.g., crank position) response of the air compressor after the compressor has charged the system and shut-off. If there is a significant leak in the valve (assuming piston not at bottom dead center), the charged air in the reservoir will bleed back through an exhaust valve to force the high pressure piston head to displace downward thus causing a response in the speed signal (or crank position) of the compressor. The exemplary systems and methods can be used as an early identification system for valve wear and failure that eventually leads to compressor failure. 
     The subject systems and methods can also be used to diagnose and prognose problems in an air compressor prior to total compressor failure, which can also result in a road failure. If onset of valve failure (leaks) can be detected in the system, proper corrective action can be provided to stop progression of failure and identify issues in the system. In this manner, customers can realize a cost savings by prognosing the problem in initial stages of failure before the valve leaks lead to other component failures and ultimate compressor failures and locomotive shutdowns. Secondary damage avoidance is also a benefit in that other engine components (pistons, liners, etc.) can be saved if leaks are detected in a early stage. 
       FIG. 1  shows a block diagram of an example embodiment of a vehicle system  100  (e.g., a locomotive system), herein depicted as a rail vehicle  106  configured to run on a rail  102  via a plurality of wheels  108 . As depicted, the rail vehicle  106  includes a compressor system with a compressor  110 . In an embodiment, the compressor is a reciprocating compressor that delivers air at high pressure. For this purpose, the compressor can compress air received via the ambient air intake  114  in a multi-stage process to generate charged air. In an example, ambient air is compressed in a first stage to a first pressure level and delivered to a second stage, which further compresses the air to a second pressure level that is higher than the first. The charged air at the second pressure level can subsequently be stored in a reservoir. 
     The compressor  110  includes a crankcase  160 . Crankcase  160  is an enclosure for a crankshaft (not shown in  FIG. 1 ) connected to cylinders (not shown in  FIG. 1 ) of the compressor. A motor  165  is employed to rotate the crankshaft to drive the pistons within the cylinders. The crankshaft may be lubricated by compressor oil that is pumped by an oil pump (not shown) and sprayed onto the crankshaft. The crankshaft in turn can be mechanically coupled to a plurality of pistons via respective connecting rods. The pistons are drawn down and pushed up as the crankshaft is rotated to generate and output charged air in one or more stages. 
     The rail vehicle  106  further includes a controller  130  to control various components related to the vehicle system  100 . In one example, controller  130  includes a computer control system. In one embodiment, the computer control system includes a processor, such as processor  132 . The controller  130  may include multiple compressor control units (ECU) and the control system may be distributed among each of the ECUs. The controller  130  further includes computer readable storage media, such as memory  134 , including instructions for enabling on-board monitoring and control of rail vehicle operation. Memory  134  may include volatile and non-volatile memory storage. 
     The controller may oversee control and management of the vehicle system  100 . The controller may receive signals from a variety of compressor sensors  150  to determine operating parameters and operating conditions, and correspondingly adjust various compressor actuators  152  to control operation of the rail vehicle  106 . For example, the controller may receive signals from various sensors including compressor speed, compressor load, boost pressure, exhaust pressure, ambient pressure, exhaust temperature, etc. As another example, the controller may receive a signal from a crankcase pressure sensor  170  that indicates a pressure of crankcase  160 . As another example, the controller may receive a signal from a crankshaft position sensor  172  that indicates a position of the crankshaft. Correspondingly, the controller may control the vehicle system by sending commands to various components such as traction motors, alternator, cylinder valves, throttle, etc. Signals from sensors  150 ,  170 , and  172  may be bundled together into one or more wiring harnesses to reduce space in vehicle system  100  devoted to wiring and to protect the signal wires from abrasion and vibration. 
     The controller may include onboard electronic diagnostics for recording operational characteristics of the compressor. Operational characteristics may include measurements from sensors  150 ,  170 , and  172 , for example. Such operational characteristics may be stored in a database in memory  134 . In one embodiment, current operational characteristics may be compared to past operational characteristics to determine trends of compressor performance. 
     The controller may include onboard electronic diagnostics for identifying and recording potential degradation and failures of components of vehicle system  100 . For example, when a potentially degraded component is identified, a diagnostic code may be stored in memory  134 . In one embodiment, a unique diagnostic code may correspond to each type of degradation that may be identified by the controller. For example, a first diagnostic code may indicate a nonfunctional exhaust valve of a cylinder, a second diagnostic code may indicate a nonfunctional intake valve of a cylinder, a third diagnostic code may indicate inappropriate compression action from a piston, etc. The controller can modify output of charged air from the compressor  110  based on various parameters including the condition of associated charged air systems (e.g., within adjacent locomotive engines), environmental conditions, overall pneumatic supply demand, etc. 
     The controller may be further linked to display  140 , such as a diagnostic interface display, providing a user interface to the locomotive operating crew and a maintenance crew. The controller may control the compressor, in response to operator input via user input controls  142 , by sending a command to correspondingly adjust various compressor actuators  152 . Non-limiting examples of user input controls  142  may include a throttle control, a braking control, a keyboard, and a power switch. Further, operational characteristics of the compressor, such as diagnostic codes corresponding to degraded components, may be reported via display  140  to the operator and/or the maintenance crew. 
     The vehicle system may include a communications system  144  linked to the controller. In one embodiment, communications system  144  may include a radio and an antenna for transmitting and receiving voice and data messages. For example, data communications may be between vehicle system and a control center of a railroad, another locomotive, a satellite, and/or a wayside device, such as a railroad switch. For example, the controller may estimate geographic coordinates of vehicle system using signals from a GPS receiver. As another example, the controller may transmit operational characteristics of the compressor to the control center via a message transmitted from communications system  144 . In one embodiment, a message may be transmitted to the command center by communications system  144  when a degraded component of the compressor is detected and the vehicle system may be scheduled for maintenance. 
     An example of a degraded component may be an exhaust valve of a compressor cylinder. Proper operation of the compressor relies upon a functional intake valve and exhaust valve associated with each cylinder. The intake valve opens to draw in air as a piston is pulled down to bottom dead center via rotation of the crankshaft (not shown). At bottom dead center the intake valve closes thereby sealing the cylinder. As the crankshaft continues to rotate, the piston is pushed up from bottom dead center to compress air contained within the cylinder to a desired pressure level before the exhaust valve opens thereby allowing the charged air to escape from the cylinder and into a reservoir  180 . This process is repeated until the reservoir is filled with charged air at a pressure level as determined by a sensor  185 . The reservoir is coupled to one or more pneumatic systems and/or devices to facilitate operation thereof. 
     After the reservoir is filled, the air system between the reservoir input and the compressor is closed and one or more pistons within the compressor are monitored. In an embodiment, a piston within a high pressure stage cylinder is monitored to determine if the piston displaces within a time period subsequent to reservoir filling. If such displacement is detected, it can be assumed that an exhaust valve is faulty as it allowed charged air to bleed back thereby forcing the piston to move down toward the bottom of the cylinder. Displacement of the piston can be accomplished by detecting the crank position or speed of the compressor using one or more compressor sensors  150 . 
     In an embodiment, the compressor is a two stroke compressor. In a two stroke compressor, the intake and exhaust functions are separated as the piston approaches bottom dead center at the end of the intake stroke and as the piston moves away from bottom dead center at the beginning of the compression stroke. The intake stroke draws air into the cylinder as the piston is pulled down by the crankshaft as it is rotated by the motor. As the crankshaft continues to rotate, the piston compresses the air in the cylinder as the piston moves toward top dead center during a compression stroke. Thus, the compressor, e.g. crankshaft  250 , may rotate once during one two stroke cycle. 
       FIG. 2  illustrates a detailed view of the compressor  110  set forth in  FIG. 1  above. The compressor includes three cylinders  210 ,  220 ,  230 . Each cylinder contains a piston  218 ,  228 ,  238  that is coupled to a crankshaft  250  via connecting rods  240 ,  242 ,  244 . The crankshaft  250  is driven by the motor  165  to cyclically pull the respective pistons down to bottom dead center and push the pistons to top dead center to output charged air, which is delivered to the reservoir  180  via air lines  280 ,  282 ,  284 ,  286 . In this embodiment, the compressor is divided into two stages: a low pressure stage and a high pressure stage to produce charged air in a stepwise approach. The low pressure stage compresses air to a first pressure level which is further compressed by the high pressure stage to a second pressure level. In this example, the low pressure stage includes cylinders  220 ,  230  and the high pressure stage includes cylinder  210 . 
     In operation, air from the ambient air intake  114  is first drawn into the low pressure cylinders via intake valves  222 ,  232 , which open and close within ports  223 ,  233 . The ambient air is drawn in as the low pressure cylinders are pulled to bottom dead center wherein the intake valves  222 ,  232  separate from ports  223 ,  233  to allow air to enter each cylinder  220 ,  230 . Once the pistons reach bottom dead center, the intake valves  222  and  232  close the ports  223 ,  233  to contain air within each cylinder. Subsequently, pistons  228 ,  238  are pushed toward top dead center, thereby compressing ambient air initially drawn into the cylinders. Once the cylinders have compressed the ambient air to a first pressure level, exhaust valves  224 ,  234  within ports  225 ,  235  are opened to release the low pressure air into low pressure lines  280 ,  282 . 
     The low pressure air is routed to an intercooler  260  to remove the heat of compression through a substantially constant pressure cooling process. A decrease in the temperature of the air allows a greater density to be drawn into the high pressure stage to facilitate a greater efficiency to provide a desired pressure level while utilizing a minimum amount of resources. The rate, volume, temperature, etc. of air exhausted from the intercooler is determined by an intercooler controller  262 . In an embodiment, the intercooler controller employs a thermostatic control through mechanical means such as via thermal expansion of metal. 
     Low pressure air exhausted from the intercooler  260  into low pressure air line  284  is subsequently drawn into the high pressure cylinder  210 . More particularly, as piston  218  is pulled toward bottom dead center, the intake valve  212  opens thereby allowing the low pressure air to be drawn into the cylinder  210  via intake port  213 . Once the piston  218  reaches bottom dead center, the intake valve  212  closes to seal the low pressure air within the cylinder  210 . The piston is then pushed upward thereby compressing the low pressure air into high pressure air. As compression increases the exhaust valve  214  is opened to allow the high pressure air to exhaust into high pressure line  286  via exhaust port  215 . An aftercooler  270  cools the high pressure air to facilitate a greater density to be delivered to the reservoir  180  via air line  288 . 
     The above process is repeated cyclically as the crankshaft  250  rotates to continuously provide high pressure air to the reservoir  180 , which is monitored by the pressure sensor  185 . Once the reservoir  180  reaches a particular pressure level (e.g., 140 psi), the pressure sensor  185  sends an output to the controller  130  to unload the compressor by actuating the unloader valve  268 , and turn off the motor  165 . In addition, the unloader valve is closed when the compressor is at rest to seal the air lines and cylinders to maintain a charged air pressure level throughout the compressor  110  for a period of time. During this period, certain valves within the compressor  110  may be evaluated to insure that they are in proper working condition. 
     In one embodiment, the exhaust valve  214  is evaluated to determine if it can maintain a closed position while under pressure. A faulty valve condition can be detected by monitoring the motion of the crankshaft  250  via a sensor  370 , which identifies displacement and/or speed of the crankshaft  250 . In this example, the crankshaft  250  does not normally move during the time period following filling of the reservoir as the motor is turned off. Thus, any movement detected by the sensor  370  can be caused by high pressure air from the air line  286  leaking into the cylinder  210  as a result of a exhaust valve  214  improperly becoming unseated from the port  215 . 
     As a result of the faulty condition of the exhaust valve  214 , air leaking into the cylinder  210  displaces the piston  218  toward a bottom dead center position. As the piston is coupled to the crankshaft via connecting rod  240 , movement of the piston  218  also turns the crankshaft  250 . As a faulty valve condition is manifested as a displaced piston, monitoring of piston displacement can be initiated subsequent each time the reservoir  180  is filled to a particular pressure level. A plurality of readings can be taken over the time period to insure that a faulty condition is identified even if one or more readings occur when the piston is in a bottom dead center position at the beginning of the time period. In this manner, it is not necessary to determine the starting position of the piston  218  within the cylinder  210 . 
       FIG. 3  illustrates an example embodiment of cylinder  210  of the compressor during a compression stroke. In this embodiment, cylinder  210  includes cylinder wall  320  and a volume for drawing in and compressing air. Piston  218  may be coupled to a crankshaft  250  by a connecting rod  240  so that the reciprocating motion of piston  218  may be translated into rotational motion of crankshaft  250 . Crankshaft  250  and connecting rod  240  are enclosed within crankcase  160 . Piston  218  reciprocates back and forth within cylinder  210  from a top dead center position to a bottom dead center position. The top dead center position corresponds to the position of piston  218  that is closest to an intake valve  312  and an exhaust valve  316 . The bottom dead center position corresponds to the position of piston  218  that is farthest from intake valve  312  and exhaust valve  316 . In one embodiment, intake valve  312  may be opened to allow air into cylinder  210  from intake passage  314 . Exhaust valve  216  may be opened to allow charged air  410  to exit cylinder  210  through exhaust passage  318 . Charged air pushed out of the cylinder via the exhaust valve  216  is directed to the reservoir for storage and subsequent use. 
       FIG. 4  illustrates the piston  218  during a time period subsequent to filling the reservoir. In this embodiment, a leaky valve  390  is employed which allows charged air  410  from the reservoir to bleed back into the cylinder  210 . The valve  390  can become faulty based on degradation of one or more valve components as the compressor is used. For example, walls of intake port  213  or exhaust port  215  may become scuffed, gouged, pitted, and/or scraped which may increase the gap between intake valve  212  and exhaust valve  214  and their respective ports  213 ,  215 . Thus, valve leakage may increase in a degraded port. In another example, intake valve  212  or exhaust valve  214  may degrade as the compressor is used. Springs, washers, o-rings, gaskets, and other valve components may shrink, potentially allowing charged air to move past the valve as a seal is not properly made. As another example, one or more valve components may warp, fracture, or be damaged in a manner that may increase air leakage. Thus, leakage may increase when one or more valve components and their respective ports are degraded. 
     If charged air  410  bleeds back into the cylinder, displacement of the piston  218  can occur from downward force  380  applied to the top of the piston. To identify such a condition, sensor  370  can be employed to determine if the piston  218  has been displaced. In this example, the sensor  370  is coupled to the crankshaft to indirectly monitor the location of the piston during a time period subsequent to reservoir filling. Displacement of the piston  218  causes movement of the crankshaft  350  as these components are mechanically coupled. In one embodiment, the sensor  370  detects speed of the crankshaft  250  using Hall effect or other measurement technology. In another embodiment, the sensor  370  detects position (e.g., rotational displacement) of the crankshaft by detecting the location of one or more features of the crankshaft  250  and/or one or more components coupled thereto. If the sensor  370  identifies a condition that indicates movement of the crankshaft subsequent to filling the reservoir, it can be inferred that the downward force  380 , caused by a leaky exhaust valve, has been applied to the piston  218 . 
       FIG. 5  illustrates a methodology  500  that can be implemented by the controller  130  to identify a leak condition of a valve within a compressor. At reference numeral  510 , operation of a reciprocating compressor is initiated to generate a desired quantity of air at a particular pressure level, which can be utilized by one or more pneumatic devices for operation thereof. At  520 , a reservoir is filled with charged air to a pressure value via the reciprocating compressor. The pressure value can be selected based upon the number and type of devices dependent thereupon the compressor output, in one example. At  530 , an unloader valve is opened on at least a high pressure cylinder, such as cylinder  210  described herein. In an embodiment, the unloader valve for several low pressure cylinders are closed as well as the high pressure cylinder. At  540 , the compressor is stopped and at  550 , the one or more unloader valves are closed to maintain charged air within the compressor for valve evaluation. 
     Once the reservoir is filled, at  560  a piston within a cylinder coupled to the reservoir is monitored. A loader valve can be closed during this time period to maintain a charged air level within the compressor. In this manner, functionality of a valve containing the charged air can be properly tested. At  570 , a determination is made whether the piston is displaced once the reservoir is filled with air. Displacement of the piston can be determined by rotational movement of a crankshaft or other member mechanically coupled to the piston. If such displacement is detected, a signal is output to indicate that a leak condition of the valve exists. If no displacement is detected (e.g., no crankshaft movement), the method returns to step  560  to continue monitoring the valve condition. In this manner, a bottom dead center placement of the piston can be overcome by obtaining a plurality of measurements over the time period as the piston will not be exclusively in a bottom dead center position. If piston displacement is detected during the time period following reservoir filling, a signal is output at  580  to indicate a leak condition of the valve. In this manner, corrective measures can be taken to address the valve leak before any serious consequence (e.g., compressor failure) results. Corrective measures can include disconnecting power to the compressor, reducing output of the compressor, switching from the compressor to another the source of charged air 
     In an embodiment, the piston location is determined immediately after reservoir filling is complete. Such location is important to insure that the sensor  370  is providing an accurate reading. For example, if the piston is located at bottom dead center, the application of force caused by the charged air  310  will not cause downward displacement of the piston as there is no room for further movement. Thus, a measurement of no displacement may not be an accurate indication that the valve  216  is in good working order. To overcome this measurement deficiency, the sensor  370  may take measurements of the crankshaft  250  over a time period and multiple compressor charge cycles to determine if a leaky valve condition exists. In this manner, it can be assumed that the piston  218  is not in the bottom dead center position every time the reservoir has been filled. Accordingly, displacement of the piston  218  can be identified during one or more alternate cycles to notify a user of such condition. If such a condition exists an audio alarm, a visual alarm, a text message, an email, an instant message, a phone call or other means can be employed to notify appropriate personnel in response to the signal output. 
     In addition, valve leakage data may be recorded. In one embodiment, valve leakage data may be stored in a database including historical compressor data. For example, the database may be stored in memory  134  of controller  130 . As another example, the database may be stored at a site remote from rail vehicle  106 . For example, historical compressor data may be encapsulated in a message and transmitted with communications system  144 . In this manner, a command center may monitor the health of the compressor in real-time. For example, the command center may perform steps, such as steps  520 ,  530 ,  540 , and  550  to diagnose the condition of the compressor using the compressor data transmitted with communications system  144 . For example, the command center may receive compressor data including cylinder pressure data from rail vehicle  106 , displacement of one or more pistons, and/or movement of the crankshaft to diagnose potential degradation of the compressor. Further, the command center may schedule maintenance and deploy healthy locomotives and maintenance crews in a manner to optimize capital investment. Historical compressor data may be further used to evaluate the health of the compressor before and after compressor service, compressor modifications, and compressor component change-outs. 
     If a faulty valve condition exists, further diagnostics and response may be performed as illustrated with an example methodology  600  shown in  FIG. 6 . At  610 , potential faulty valve condition can be reported to notify appropriate personnel. In an embodiment, reporting is initiated with signal output to indicate a leak condition of the valve exists, from step  550  in  FIG. 5 . The report may be via display  140  or a message transmitted with communications system  144 , for example. Once notified, the operator may adjust operation of rail vehicle  106  to reduce the potential of further degradation of the compressor. 
     In one embodiment, a message indicating a potential fault may be transmitted with communications system  144  to a command center. Further, the severity of the potential fault may be reported. For example, diagnosing a fault based on rotational displacement of the crankshaft  250  pressure may allow a fault to be detected earlier than when the fault is diagnosed with other means. Thus, the compressor may continue to operate when a potential fault is diagnosed in the early stages of degradation. In contrast, it may be desirable to stop the compressor or schedule prompt maintenance if a potential fault is diagnosed as severe. In one embodiment, the severity of a potential fault may be determined according to a difference between a threshold value and the magnitude of rotational displacement and/or speed of the crankshaft. In this manner the cost of secondary damage to air compressor by early and accurate detection can be avoided. 
     At  620 , the severity of the potential fault may be compared to a threshold value. For example, it may be more desirable to switch off the compressor than to have a degraded cylinder fail in a manner that may cause additional damage to the compressor. In one embodiment, a threshold value may be determined that indicates continued operation of the compressor may be undesirable because the potential fault is severe. For example, the potential fault may be judged as severe if the crankshaft is moved beyond a particular angle of rotation. The compressor may be stopped, at  625 , if the severity of the potential fault exceeds the threshold value. Otherwise, method  600  may continue at  630 . 
     At  630 , a request to schedule service may be sent, such as by a message sent via communications system  144 , for example. Further, by sending the potential fault condition and the severity of the potential fault, down-time of rail vehicle  106  may be reduced. For example, service may be deferred on rail vehicle  106  when the potential fault is of low severity. Down-time may be further reduced by derating power of the compressor, such as by adjusting a compressor operating parameter based on the diagnosed condition. 
     At  640 , it may be determined if backup of the compressor is enabled. In an example, backup systems can be evaluated to determine if adequate substitute resources exist to replace the compromised compressor. In some instances, a pre-ordered list of backup systems is used to prioritize backup systems. If a backup is enabled, a backup procedure is implemented at  650 . If no backup is enabled, the method  600  ends. At  650 , the backup procedure can include stopping the compressor and receiving charged air from another source. In one example, the other source is a compressor that is disposed on an adjacent locomotive engine. In another example, the other source is a redundant compressor on the same locomotive that is used for this purpose. The backup procedure can be designed to minimize negative system-wide consequences to operation of the locomotive. This is especially true for systems deemed to be critical such as braking systems, which rely on charged air to operate. In such instances, a backup system is necessary to prevent shut down of the locomotive. 
     In one embodiment, a test kit may be used for identifying faulty compressor valve condition and diagnosing a condition of the valve based on the movement of the crankshaft. For example, a test kit may include a controller that is operable to communicate with one or more sensors coupled to crankcase and operable to sense crankshaft speed and/or rotation. The controller may be further operable to transform signals from the one or more sensors into a an output that represents a faulty valve condition and severity thereof. For example, severity of a faulty valve can be correlated with the amount of rotation of the crankshaft as more air is allowed into the cylinder as the severity of the leakage condition increases. 
     In an embodiment, a method is employed for a reciprocating compressor to detect a leak condition of a valve via recognition of displacement of an associated piston. Such displacement is caused by air flow through the valve during a time period in which no piston motion is expected. A reservoir is filled with air to a pressure value, wherein the reservoir is coupled to a cylinder that includes piston within a closed air circuit, wherein an exhaust valve is disposed between the reservoir and the cylinder. A determination is made as to whether the piston is displaced once the reservoir is filled to the pressure value. A signal is output to indicate the leak condition of the valve within the closed air circuit if the piston is displaced. Displacement of the associated piston is detected via a sensor that monitors a crankshaft position within the reciprocating compressor. 
     As described herein, no piston motion is expected during periods of time in the compressor cycle when one or more conditions are satisfied. Conditions can include whether the reservoir has been filled to a pressure level; a time period has been met that relates to particular heat, work, current draw, etc. of the motor, which can be associated with deleterious consequences; a pre-programmed cycle time has expired; or other metrics that facilitate efficient motor operation to produce charged air for storage in the reservoir. Alternatively or in addition, even when a condition has been satisfied, one or more additional evaluations can be employed including whether power is delivered from the motor to the compressor and whether the speed, displacement, and/or pressure sensors output a value that is significant relative to a threshold. For example, a value output from a speed or displacement sensor may be below a threshold whereas a pressure sensor may be above a threshold to qualify as a no motion state. 
     In an embodiment, a method is employed for a reciprocating compressor to detect a leak condition of a valve via recognition of displacement of an associated piston. Such displacement is caused by air flow through the valve during a time period in which no piston motion is expected. An unloader valve is closed during the time period to facilitate a pressurized state within the reciprocating compressor, the unloader valve forces open an intake valve to one or more cylinders in the air compressor. 
     In an embodiment, a method is employed for a reciprocating compressor to detect a leak condition of a valve via recognition of displacement of an associated piston. Such displacement is caused by air flow through the valve during a time period in which no piston motion is expected. An unloader valve is opened during the time period to facilitate an unpressurized state within the reciprocating compressor, the unloader valve forces open an intake valve to one or more cylinders in the air compressor. 
     In an embodiment, a method is employed for a reciprocating compressor to detect a leak condition of a valve via recognition of displacement of an associated piston. Such displacement is caused by air flow through the valve during a time period in which no piston motion is expected. The reciprocating compressor supplies charged air within a locomotive. 
     In an embodiment, a method is employed for a reciprocating compressor to detect a leak condition of a valve via recognition of displacement of an associated piston. Such displacement is caused by air flow through the valve during a time period in which no piston motion is expected. The time period begins once a reservoir coupled to the reciprocating compressor meets or exceeds a pressure level value. 
     In an embodiment, a method is employed for a reciprocating compressor to detect a leak condition of a valve via recognition of displacement of an associated piston. Such displacement is caused by air flow through the valve during a time period in which no piston motion is expected. A signal is output in response to recognition of displacement of the associated piston. Power to the reciprocating compressor is disconnected in response to the signal output. 
     In an embodiment, a method is employed for a reciprocating compressor to detect a leak condition of a valve via recognition of displacement of an associated piston. Such displacement is caused by air flow through the valve during a time period in which no piston motion is expected. A signal is output in response to recognition of displacement of the associated piston. Personnel are notified via one or more of an audio alarm, a visual alarm, a text message, an email, an instant message, and a phone call in response to the signal output. 
     In an embodiment, a method is employed for a reciprocating compressor to detect a leak condition of a valve via recognition of displacement of an associated piston. Such displacement is caused by air flow through the valve during a time period in which no piston motion is expected. A signal is output in response to recognition of displacement of the associated piston. The flow of charged air to the reciprocating compressor is engaged from one or more other sources in response to the signal output. 
     In an embodiment, a method is employed for a reciprocating compressor to detect a leak condition of a valve via recognition of displacement of an associated piston. Such displacement is caused by air flow through the valve during a time period in which no piston motion is expected. A signal is output that is commensurate with a severity level of the leak condition, wherein the severity level is determined according to displacement of the associated piston. 
     In an embodiment, a test kit includes a controller that is operable to determine a condition of a reciprocating compressor based on displacement of a piston during a time interval subsequent to a reservoir filled to a pressure level. Displacement of the piston is indicative of a valve leak within the reciprocating compressor. One or more sensors detect parameters associated with air pressure subsequent to filling the reservoir to predetermined level, wherein the controller is operable with the one or more sensors to sample the parameter measurements. 
     In an embodiment, a test kit includes a controller that is operable to determine a condition of a reciprocating compressor based on displacement of a piston during a time interval subsequent to a reservoir filled to a pressure level. Displacement of the piston is indicative of a valve leak within the reciprocating compressor. The controller is further operable to transform crankshaft speed into a pressure parameter within the crankshaft. 
     In an embodiment, a test kit includes a controller that is operable to determine a condition of a reciprocating compressor based on displacement of a piston during a time interval subsequent to a reservoir filled to a pressure level. Displacement of the piston is indicative of a valve leak within the reciprocating compressor. An unloader valve is closed while the reservoir is filled and during a subsequent time interval thereafter. 
     In an embodiment, a reciprocating compressor includes a plurality of pistons, each piston is coupled to a crankshaft and disposed within a respective cylinder. A reservoir stores charged air output by the cylinders. An exhaust valve allows air compressed by each piston to transmit from the respective cylinder to the reservoir. An intake valve allows air to enter each respective cylinder prior to displacement of the piston. A sensor measures at least one metric during a time period that is indicative of a leak condition of each exhaust valve. Each of the plurality of pistons are not in a bottom dead center position at the beginning of the time period. 
     In an embodiment, a reciprocating compressor includes a plurality of pistons, each piston is coupled to a crankshaft and disposed within a respective cylinder. A reservoir stores charged air output by the cylinders. An exhaust valve allows air compressed by each piston to transmit from the respective cylinder to the reservoir. An intake valve allows air to enter each respective cylinder prior to displacement of the piston. A sensor measures at least one metric during a time period that is indicative of a leak condition of each exhaust valve. A sensor measures a position of the crankshaft, wherein the position of the crankshaft indicates a leak condition for the valve. 
     In an embodiment, a method is employed for a reciprocating compressor operationally connected to a reservoir. The reservoir is filled to meet or exceed a pressure level. A valve disposed between the reservoir and one or more cylinders is closed, wherein each cylinder houses a piston, the piston is not in a bottom dead center position. If piston motion is detected, a signal is output to indicate that the valve has a leakage condition. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable one of ordinary skill in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that are not different from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.