Patent Publication Number: US-2006013698-A1

Title: Locomotive air compressor system with enhanced protection against leakage causative of backflow of pressurized air from a reservoir

Description:
This application claims the benefit of U.S. application Ser. No. 60/587,448, which is hereby incorporated by reference in its entirety.  
     FIELD OF THE INVENTION  
      The present invention is directed to air compressor systems for railroad locomotives, and, more particularly, to an air compressor system with enhanced protection against leakage that may cause backflow of pressurized air from a reservoir.  
     BACKGROUND OF THE INVENTION  
      It is known to use multi-cylinder air compressors on freight and passenger locomotives to supply compressed air to a main storage reservoir and in turn to various locomotive systems, such as the operating and control equipment of a railway air brake system.  
      One issue that has affected such compressor systems may arise due to leakage of pressurized air from the main storage reservoir into a high-pressure cylinder of the compressor system. This can cause a buildup of pressure in the high-pressure cylinder that must be overcome by a rotatable prime mover (e.g., electric motor) of the air compressor system. That is, the compressor motor may be forced to supply a relative high level of starting torque in order to overcome the buildup of backpressure in the high-pressure cylinder. This is undesirable because this can detrimentally affect the expected life of the motor and can lead to premature wear and tear and malfunctions of various mechanical, electrical or electromechanical components of the air compressor system.  
      One known technique that has been used for reducing the possibility of performing hard motor starts may entail time-consuming and burdensome operations. For example, this known technique may require the following operations: access to the piping connected to the inlet valves of the high-pressure cylinder, connecting a pressure source to pressurize the piping. The pressurization level is selected sufficiently high to cause opening of the inlet valves of the high cylinder so that the buildup of pressure in the high cylinder passes through those open valves and through the piping connected to those valves to be eventually vented to the surrounding environment at an appropriate outlet. It will be appreciated that the foregoing technique (leaving aside the incremental burdens required for performing it) for reducing the possibility of hard motor starts is just a partial solution since that technique does not address the loss of pressurized air that occurs from the main storage reservoir to the high pressure cylinder in the event a leakage condition develops at the outlet valves of the high pressure cylinder. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      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:  
       FIG. 1  illustrates a schematic representation of an exemplary locomotive air compressor system embodying aspects of the present invention.  
       FIG. 2  schematically illustrates an exemplary piping assembly for providing a pneumatic connection between a pair of outlet valves in the high pressure cylinder of the air compressor system of  FIG. 1  and a main storage reservoir.  
       FIG. 3  illustrates a sectional view of respective spring-loaded inlet and outlet valves in a high-pressure cylinder of the air compressor system of  FIG. 1 .  
       FIGS. 4A and 4B  respectively illustrate open and closed conditions of a valve, such as a ball check valve, having a set of sealing characteristics different than the sealing characteristics of the valves illustrated in  FIG. 3 .  
       FIGS. 5A and 5B  respectively illustrate open and closed conditions of a valve, such as a swing check valve, having a set of sealing characteristics different than the sealing characteristics of the valves illustrated in  FIG. 3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 1  shows a locomotive air compressor system  10  that in one exemplary embodiment comprises a multi-cylinder, two-stage, air-cooled compressor. A first stage (e.g., a low-pressure stage) includes a first low-pressure cylinder  20  and a second low-pressure cylinder  22 . A second stage (e.g., a relatively high pressure stage) includes a high-pressure cylinder  24 . Each of such cylinders 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 . One end of the crankshaft  28  may be coupled to and driven by a suitable rotatable prime mover, such as an electric motor (not shown), while the other end of the crankshaft  28  may be attached to a rotary cooling fan assembly  29 .  
      Each low-pressure cylinder includes a pair of inlet valves  30 . A pair of outlet valves  40  of the low-pressure cylinder  20  (only one shown) may be connected to an inlet header of a first intercooler  12 . Typically, the valves may be spring-loaded valves responsive to negative or positive pressure to reach either a closed or an open condition.  
      An outlet header of intercooler  12  is connected to one inlet of a T-pipe fitting  44 . Similarly, a pair of outlet valves  46  of the low-pressure cylinder  22  is connected to an inlet header of a 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 a pair of inlet valves  50  of the high-pressure cylinder  24 . A pair of outlet valves  52  of the high pressure cylinder  24  is connected by way of a T-pipe fitting  54  and a pair of conduits  56   1  and  56   2  to the inlets of a main storage reservoir  58  ( FIG. 2 ). In one exemplary embodiment, conduit  56   1  may be directly connected to the main storage reservoir while conduit  56   2  may be connected through a heat exchanger (not shown).  
      In operation, once the main storage reservoir has been pressurized to a desired pressure level and the compressor system is in an “off” or “unloaded” state, outlet valves  52  in theory should fully close so that there is no further flow communication between the main storage reservoir and the high-pressure cylinder. In practice, however, it has been observed that outlet valves  52  often fail to provide an appropriate sealing function relative to the main storage reservoir. As illustrated in  FIG. 3 , each inlet and outlet valve  50  and  52  of the high-pressure cylinder  24  comprises spring-loaded valves responsive to negative or positive pressure to reach either a closed or an open condition. In operation, the environment within the high-pressure cylinder head may, for example, contain oil residues that may lead to buildup of oil debris and detrimentally affect the sealing function of the valves therein. Also the spring-load characteristics of the valves may be affected, for example, due to wear and tear and this can also detrimentally affect the sealing function of the valves in the high-pressure cylinder.  
      More particularly, the tendency to leak of outlet valves  52  can lead to undesirable backflow of pressurized air from the main storage reservoir into the high-pressure cylinder. The leakage of pressurized air from the main storage reservoir can cause the pressurization of that reservoir to fall below a desired pressure level, and this in turn can lead to incremental running of the air compressor system to compensate for such a loss of pressurized air, thereby causing unnecessary additional operational costs and incremental wear and tear to the air compressor system. Moreover, during a subsequent start of the compressor system, the leakage of pressurized air from the main storage reservoir into the high-pressure cylinder  24  can cause a buildup of pressure in the high-pressure cylinder that must be overcome by the rotatable prime mover of the air compressor system.  
      The inventors of the present invention have recognized an innovative improvement that addresses the foregoing issues without having to undertake any expensive and time-consuming redesign of the air compressor system. More particularly, the present inventors have recognized that the interior of the T-pipe fitting  54  may be used for accommodating a check valve  60  responsive (e.g., mechanically responsive) to operational conditions of the air compressor system to reach either a fully closed or a fully open condition.  
      For example, when the air compressor system is in an “on” or a “loaded” condition (e.g., while generating pressurized air), then valve  60  should be in a fully open condition so that flow communication is fully maintained between the high pressure cylinder  24  and the main storage reservoir. Conversely, upon reaching a desired level of pressurization in the main storage reservoir, and the compressor system reaching an “off” or an “unloaded” condition (e.g., stoppage of generating pressurized air), then valve  60  should be in a fully closed condition. In this manner, regardless of any leakage condition that may develop in the outlet valves  52  (only one valve shown in  FIG. 2 ), one can maintain a substantially tight pressure seal between the high-pressure cylinder  24  and the main storage reservoir. Preferably, valve  60  is of another and different construction from that of the spring-loaded relief-type outlet valves in the high-pressure cylinder, so that valve  60  complements the sealing functionality provided by the outlet valves to prevent undesirable reverse direction air flow in the system while at the same time minimizing any addition of friction-induced head loss during normal direction air flow when the compressor is operating. In one exemplary embodiment, valve  60  may comprise a ball check valve, as schematically illustrated in  FIGS. 4A and 4B .  
      The condition illustrated in  FIG. 4A  corresponds to a condition when the air compressor system is in an “on” (e.g., while generating pressurized air), wherein valve  60  is in a fully open condition so that flow communication is fully maintained between the high-pressure cylinder  24  and the main storage reservoir. Upon reaching a desired level of pressurization in the main storage reservoir, and the compressor system reaching an “off” or an “unloaded” condition (e.g., stoppage of generating pressurized air), then valve  60  is set in a fully closed condition, as illustrated in  FIG. 4B . Advantageously, a valve of such design provides the reverse flow isolation capability with a minimal increase in forward flow pressure head loss.  
      In another exemplary embodiment, valve  60  may comprise a swing check valve, as schematically illustrated in  FIGS. 5A and 5B . The condition illustrated in  FIG. 5A  corresponds to a condition when the air compressor system is in an “on” or a “loaded” condition (e.g., while generating pressurized air), wherein valve  60  is in a fully open condition so that flow communication is fully maintained between the high-pressure cylinder  24  and the main storage reservoir. Upon reaching a desired level of pressurization in the main storage reservoir, and the compressor system reaching an “off” or an “unloaded” condition (e.g., stoppage of generating pressurized air), then valve  60  is set in a fully closed condition, as illustrated in  FIG. 5B . As in the example of a ball check valve, a swing check valve provides the reverse flow isolation capability with a minimal increase in forward flow pressure head loss.  
      It will be now appreciated by those skilled in the art that the sealing functionality provided by check valve  60  (between the high-pressure cylinder and the main storage reservoir) complements the sealing functionality provided by the outlet valves in the high-pressure cylinder with respect to the main storage reservoir. It is noted that in view of the distinct environment for the check valve and the structural and functional differences between the check valve and the outlet valves in the high-pressure cylinder, the incremental sealing functionality provided by added check valve  60  is complementary rather than just duplicative of the functionality provided by the outlet valves in the high-pressure cylinder.  
      The above-described structural modification is particularly attractive since it lends itself to retrofit operations that, in order to be successful, are generally required to meet the following exemplary criteria: little or no impact to field-deployed hardware; a relatively low-cost impact to the retrofit; user-friendly installation operations that may be performed without expensive equipment and tools and without having to provide any substantial training to service personnel; and essentially being transparent regarding the basic design and functionality of the compressor system (no requirements for having to re-qualify the design of the compressor system). It is believed that the present invention meets the foregoing criteria while providing lower operational costs and providing incrementally higher operational reliability and durability for the air compressor system.  
      Another exemplary embodiment may utilize a separate check valve for each of the connecting pipes  56 . This embodiment may add some redundancies against some possible failure modes. For example, in the event one of the check valves were to become stuck in a closed condition and one of the pipes  56  was no longer in flow communication with the reservoir, then the other check valve and the other pipe would still allow for flow communication from the high pressure cylinder to the reservoir.