Abstract:
A device that relieves lubricant pressure in a divider block lubrication system into a fluid reservoir, a container, or directly back into the compressor frame to which the tubing is connected. This eliminates housekeeping, environmental, safety, and compressor component failure concerns associated with current atmospheric rupture assemblies that relieve directly to the atmosphere. The environmental compressor protection assembly contains a spring set to a pre-determined pressure. Lubricant pressure in excess of this pre-determined set pressure results in spring compression and opening of a relief path. The assembly preferably remains in a full open position and must be must be manually reset to the closed position to prevent fluid flow in the system. The relief path can lead to a fluid reservoir, a container, or directly back into the compressor frame. Flow of lubricant through the relief path results in loss of flow to the lubrication system. This triggers an alarm in the no-flow system and shutdown of the compressor. The relief path remains open until an operator resets the device. A visual indicator shows an operator if the relief valve is open or closed.

Description:
This application claims priority from U.S. Provisional Patent Application No. 60/849,556, filed on Oct. 4, 2006, which is herein incorporated by reference. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to pressure relief systems for positive displacement fluid distribution systems, such as high pressure, low volume systems used to deliver lubricant to natural gas compressors. 
     BACKGROUND OF THE INVENTION 
     Compressors and other machines use lubricants distributed by lubrication systems to reduce internal friction between parts by injecting the lubricant, such as oil or grease, into critical bearing surfaces and reciprocating parts junctions. 
       FIG. 1  shows a schematically typical lubrication system  100  for natural gas compressors  101 . Such systems typically include a high pressure, low volume, positive displacement oil pump  102  including a lubricator gear box  104  that drives multiple lubricator pump roller rocker assemblies  106 . Fluid is supplied to the system from a low pressure oil supply  108 . Pressure valves  110 , one for each roller rocker assembly  106  indicate the pressure at the pump outlets. The lubricant is pumped to divider blocks  120 , each having multiple outlets  122  to distribute a desired amount of lubricant to lubricated equipment, such natural gas compressors  101 , shown schematically without connections to divider blocks  120 . The fluid pressure at the outlet of pump  102  is typically greater than about 500 psi, and the volume dispensed is typically less than about 10 or 15 gallons per day. 
     If a blockage occurs in the lubrication system, the positive displacement nature of the pump can cause a dramatic increase in the pressure in the lubrication system  100 , which can cause components in the lubrication system to fail. Non-positive-displacement-pump lubrication systems, such as systems that use centrifugal or diaphragm pumps, are not as susceptible to damage from over pressure conditions. To prevent high pressure from damaging equipment in lubrication system  100 , compressor lubrication systems typically include atmospheric rupture assemblies  132  as pressure relief devices.  FIGS. 2 and 3  show a typical atmospheric rupture assembly  132 .  FIG. 2  shows that atmospheric rupture assembly  132  includes a metal disc  202  that prevents fluid flow under normal operating conditions but that ruptures when the pressure in the system  100  exceeds a certain value, venting the lubricant to atmosphere as shown in  FIG. 3 . If the flow of lubricant is interrupted, compressors and other industrial tools can be seriously damaged or destroyed. The rupture of the disk  202  of atmospheric rupture assembly  132  causes such an interruption of lubricant flow. To protect the equipment, a sensor on a “no-flow device” (not shown) is typically used to detect this loss of lubricant flow, and to trigger an alarm and eventual shutdown of the lubricated equipment. 
     Release of lubricant at very high pressures (up to about 7400 psi) to the atmosphere raises housekeeping, safety, and environmental concerns. After the initial rupture of the metal disc  202 , lubricant is released onto the compressor frame and skid. The lubricant continues to flow until the compressor  130  is shut down by a lubricant no-flow device sensor device. The duration of continued flow varies from about a three minute interval for a digital no-flow device to about a twenty minute interval with an old style mechanical no-flow device. The resulting oil spill can be of significant size, is virtually impossible for the operator in the field to clean up, and raises environmental concerns. 
     Atmospheric rupture assemblies also raise safety concerns for workers in the area of the equipment. It is common for an operator to be near the compressor skid, monitoring pressure on a pressure gauge. The pressure gauge and lubricator pump are always in the same location as the atmospheric rupture assembly  132 . The rupture of such assemblies has resulted in operators being struck by the high pressure lubricant and injured by pieces of the aluminum disc which blew out of the assembly when it ruptured. 
     Another problem with atmospheric rupture assemblies  132  is that they allow operators to insert more than one rupture disc  202 . The installation of more than one rupture disc  202  in an assembly designed for a single rupture disc increases the pressure require to vent the system. Even with a blockage, the lubrication system may not be capable of achieving sufficient pressure to rupture multiple disks. This is a serious concern for the protection of the compressor components because the increased pressure may cause the divider block components and tubing to fail. If the excessive pressure is not relieved by the atmospheric rupture assembly, the compressor will continue to operate, potentially destroying the internal cylinder and rod packing components. The cost of replacement parts and lost production can be thousands of dollars. 
     Thus, while atmospheric rupture assemblies normally protect against high pressure damage, they have numerous shortcomings. Therefore, there is a need for a compressor protection assembly that reliably protects against excessive lubricant pressure without housekeeping, environmental, safety, and operating concerns. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide protection against excessive pressure in a high pressure, low volume fluid distribution system. 
     The current invention provides a pressure relief system that allows fluid in a system using a positive displacement pump to flow to a safe location if the pressure in the system exceeds predetermined value. In preferred applications, when a lubrication system is over pressurized, the lubricated equipment is shut down, directly or indirectly, by a protection device and cannot be restarted until the problem is corrected. The problem in the system preferably must be corrected by an operator or mechanic before the system can be restarted. Normal fluid flow is not restored automatically when the pressure drops, thereby allowing an operator to investigate and correct the source of the problem before normal operating fluid flow is restored. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows schematically a typical prior art lubrication system for a natural gas compressor, using an atmospheric rupture assembly for pressure relief. 
         FIG. 2  illustrates a typical prior art atmospheric rupture assembly in a normal operating mode. 
         FIG. 3  illustrates the typical prior art atmospheric rupture assembly of  FIG. 2  after the disc has ruptured. 
         FIG. 4  illustrates an embodiment of an environmental compressor protection assembly in a normal operating mode. 
         FIG. 5  illustrates the embodiment of  FIG. 3A  after it has reacted to an over-pressure in the system. 
         FIG. 6  illustrates an alternate embodiment of an environmental compressor protection assembly in a normal operating mode (relief valve closed), in which a cap, rather than an indicator pin, rises to indicate that the valve has opened. 
         FIG. 7  illustrates the alternate embodiment of  FIG. 6  after it has reacted to an over-pressure in the system (relief valve open). 
         FIG. 8  shows a pictorial view of the closed valve shown in  FIG. 6 . 
         FIG. 9  shows a pictorial view of the open valve shown in  FIG. 7 . 
         FIG. 10  shows an exploded view of the valve of  FIGS. 6-9 . 
         FIG. 11  shows a pictorial view of the end cap of  FIGS. 6-10 . 
         FIG. 12  shows a pictorial view of the end plug of  FIGS. 6-10 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Embodiments of the current invention eliminate environmental contamination from oil spills on compressor skids; protect compressor operators from possible injury caused by high pressure oil squirting from a blown rupture disc; prevent compressor component failure by opening at specified pressure; contain a visual indicator that notifies compressor operators of system overpressure conditions; remain in the open position until reset by an operator; and can be set to different opening pressures. 
     A typical embodiment of the pressure relief system is referred to as an Environmental Compressor Protection Assembly (“EPR™”) or a Pop Open Pressure Relief (“POPR™”) valve. Embodiments of the pop open pressure relief valve are typically used in lubrication systems that include positive displacement pumps and that provide a relatively low volume of lubricant at a relatively high pressure. During normal operation, a pop open pressure relief valve is closed. When a specified pressure is exceeded, the relief valve opens to a fully open position routing high pressure fluid through a relief passage to a safe location, such as the lubrication reservoir or the compressor crankcase. The relief valve preferably remains fixed in the open position once opened, and a visible indicator shows an operator that the valve has opened. This “fixed open” state assures the operator that the compressor will be shut down by the existing lubricant no-flow device, that is, the device that senses that no lubricant is flowing and automatically shuts down the compressor. The relief valve preferably cannot open at high pressure and then automatically reset to close when the system pressure is reduced, as relief valves currently known to the industry operate. If the relief valve remains partly open or closes automatically after the pressure is relieved in the system, the cause of the over pressure condition could remain undiscovered and cause equipment failure. In a preferred design the relief valve remains open until manually closed. This operation essentially prevents any lubricant from flowing to the compressor, the compressor will remain shut down until the blockage in the system is fixed and the operator resets the relief valve to the normal closed position. The invention protects the environment, the operator, and the compressor equipment in the event of lubricant overpressure. 
     In a first embodiment, the POPR valve assembly includes a housing that connects to the fluid distribution system and includes a relief passage to route fluid when the system pressure exceeds a predetermined value. A relief valve mechanism includes a piston that is slidable within the housing. The piston has an open position in which fluid from the fluid distribution system can enter the relief passage, and a closed position in which fluid from the fluid distribution system is prevented from entering the relief passage. A biasing element maintains a force on the piston to keep it in the closed position when the biasing force on the piston exceeds the fluid force on the piston. When the system pressure exceeds a predetermined value, the fluid force on the piston exceeds the spring force on the piston and the piston moves into the open position. A catch keeps the piston in the open position once it has been moved to the open position by the fluid pressure. A visible indicator to indicate to an observer when the piston is in the open position. 
       FIGS. 4 and 5  show a first embodiment of a POPR assembly  410 , including a piston  442 , a spring  450 , a relief passage  430 , a conduit  432  connecting the relieved lubricant to a fluid reservoir, such as external tank or a compressor crankcase (not shown), a retaining lever  460 , and an indicator  428 .  FIG. 4  shows the normal operating position in which the relief path is blocked.  FIG. 5  shows the over-pressure position in which the relief path is open. 
     The first embodiment of the POPR  410  comprises a two-section housing assembly, including a first housing section  412  having a first threaded end  414  that screws into a component (not shown) of the lubrication system, and a second threaded portion  424  for connecting a second housing section  422 . The second housing section  422  includes internal counterpart threads  420  for attaching the second threaded portion  424  of the first housing section  412 , and an opposing end having an opening  426  from which the indicator  428  can protrude to indicate that the valve has opened. The POPR  410  includes a shaft  440  that extends within housing sections  412  and  422 . The piston  442  attached to the shaft  440  in the first housing section  412  moves about an internal passage  444  of the first housing section  412 . The piston  442  and an o-ring  448  prevent the lubricant from entering the relief passage  430 . 
     As shown in  FIG. 4 , during normal operation, the piston  442  is pushed down by the pressure of the spring  450 . The spring  450  inside the second housing section  422  is maintained in position by a disc  452  that is not free to slide downward on the shaft  440 . The spring  450  pushes against the disc  452 , which exerts a force on the shaft  440  to keep the piston  442  in the closed position. 
     When blockage takes place in the system, the pressure gradually builds until the spring pressure is overcome. As shown in  FIG. 5 , when the lubricant pressure exceeds the exerted pressure of the spring  450 , the piston  442  moves further into the first housing section  412 , forcing the disc  452  up and compressing the spring  450 , exposing the internal passage  444  to the relief passage  430  between the lubrication system and the conduit  432  which connects to a fluid reservoir. The term “fluid reservoir,” used to indicate any enclosure in which the lubricant or other fluid can be directed, as opposed to the prior art in which the lubricant is discharged onto the ground. A fluid reservoir can include, for example, external tank, a container, or a compressor crankcase (not shown). A conduit  432 , such as a tube or a pipe, is connected to the relief passage  430  using various fittings. The pressure required to open the internal passage  444  to the relief passage  430  depends on the force of spring  450 . Therefore, the set pressure can be changed by installing a spring  450  with a different spring constant, that is, a stiffer or weaker spring. Additional O-rings  462 ,  464 , and  466  seal the unit and prevent lubricant or contaminants from entering. 
     A visual indicator notifies the operator of the blockage and/or over-pressure condition of the system. This blockage can occur in the divider valve, check valves, tubing lines or injection points of the fluid distribution system. In one embodiment, an indicator  428  on the end of the shaft  440  protrudes though the opening  426  in the second housing section  422 , indicating to an operator that the POPR  410  has opened.  FIG. 4  shows the POPR  410  in the normal closed position, with the indicator  428  hidden inside the opening  426 .  FIG. 5  shows the POPR  410  in the open position, with the indicator  428  protruding through the opening  426 . In an alternate embodiment, as shown in  FIGS. 6 and 7 , a cap rises to indicate that the valve has opened. 
     As shown in  FIGS. 4 and 5 , the shaft  40  passes through the retaining lever  460 , which allows the shaft  440  to move in the direction of opening the valve, but prevents the shaft  440  from moving back to close the valve again after the pressure in internal passage is reduced. The retaining lever  460  provides a frictional force that is counter to and greater than the force from spring  450 . Thus, once the valve has opened, it will remain open until serviced by an operator. This open state assures the operator that the compressor will be shut down by the lubricant no-flow device (not shown). As such, the compressor cannot operate until the blockage in the system is fixed and the retaining lever  460  is manually lifted by the operator to enable the lubricant to flow through the system. When the operator lifts the retaining lever  460 , the frictional pressure on the shaft  440  is released. Under pressure from the spring  450 , piston  422  moves to close relief passage  430  and restore fluid flow to the lubricated equipment. The POPR  410  is thus reset to the default closed position as shown in  FIG. 4 , with the visual indicator  428  disappearing inside the opening  426  of the assembly. 
     Some embodiment of the invention depends on a separate lubrication system no-flow device to shut down the compressor after the valve opens to divert the lubricant. In other embodiments, the opening of the valve itself activates a switch to shut down the lubricated equipment. For example, a micro switch  470  at the top of the POPR valve  410  may communicate to a compressor control panel via a wire  472  or by a wireless connection, such as an infrared or radio frequency connection. When the POPR valve opens, the movement of the valve components can activate the switch  470  to send a signal to the control panel causing the compressor to be immediately shut down. Such embodiments can provide an immediate shut down of the compressor when the lubricant flow stops and eliminates dependence on the no-flow device in the hydraulic system to indicate an alarm and shut down the compressor. These embodiments also provide a redundant shutdown protocol if either of the shutdown devices fails to operate correctly. A preferred switch could be incorporated into the valve body or, like switch  470 , added externally onto the valve housing, depending on the application. Any suitable switch could be used, for example, Hall effect sensor or reed switch that is activated by a magnet on the piston or another moving part or a switch that is activated by the moving valve components making or breaking an electrical contact or optical connection, keeping in mind that any switch may need to be explosion proof, depending on the environment in which the switch is used. It is preferably that the compressor shuts down immediately when the flow of lubricant to the compressor components is interrupted, rather than waiting for the lack of flow to be sensed by a separate no flow sensor. 
       FIGS. 6-12  show an alternative embodiment of a POPR valve  600 , with  FIGS. 6 and 8  showing the POPR valve  600  in the closed position and  FIGS. 7 and 9  showing the POPR valve  600  in the open position.  FIG. 10  shows an exploded view of the POPR valve  600 . POPR valve  600  includes a main housing  602  and an end cap  604 .  FIG. 11  shows a pictorial view of end cap  604 . As shown in  FIGS. 6 and 7 , main housing  602  includes a hollow male threaded end  605  that is threaded into a lubrication system component  640  and provides an inlet  611  for high pressure fluid. The high pressure fluid exerts a force against a piston  612  that can slide within a hollow cylindrical sleeve  614 . Press fit end cap  615 , in the shape of a plug with a longitudinal slice removed ( FIG. 12 ), keeps piston  612  within housing  602  while allowing fluid to enter inlet  611 . O-rings  618  and  620  provide seals around piston  612  on either end of sleeve  614 . A hole  1002  ( FIG. 10 ) through sleeve  614  perpendicular to the sleeve&#39;s long axis allows fluid to escape through relief path  630  when the incoming fluid pressure forces piston  612  past o-ring  618  and sufficiently far to open a path from inlet  611  to escape path  630 . Like relief passage  430  of the embodiment of  FIGS. 4 and 5 , relief path  630  connects to a fluid reservoir external tank, a container, or a compressor crankcase (not shown) so that the fluid is not sprayed out into the environment, as happens with prior art rupture valves. A biasing force maintains the piston  612  extending beyond o-ring  618  during normal operating conditions, sealing off relief passage  630 . 
     End cap  604  includes a mechanism to maintain POPR valve  600  in the open position after an over pressure condition occurs and to provide a visual indicator to the operator that the valve has been opened. When piston  612  moves to open a passage to relieve path  630 , the piston pushes end cap  604  partly out of main housing  602 . The portion  902  ( FIG. 9 ) of end cap  604  that is exposed when end cap  604  is displaced is preferably brightly colored so that an operator can readily see that the end cap  604  has been displaced. A plug  650  is threaded into end cap  604  to trap a spring  652  and a spring holder  654  in end cap  604 . A cavity  658  in end cap  604  includes within it balls  660  and  662 . 
     As shown most clearly in  FIGS. 10 and 11 , end cap  604  includes in its outer diameter a flat indentation  1002  through which extends a hole  1004 , having a diameter slightly larger than that of balls  660  and  662 . After end cap  604  is inserted into main housing  602 , a dowel pin  664  is inserted into a hole  1006  ( FIG. 10 ) in main housing  602 . Dowel pin  666  fits within indentation  1002 , trapping end cap  604  within housing  602 . Under normal operating pressures, spring  652  presses spring holder  654  against ball  660 , which forces ball  662  partly into hole  1004 . End cap  604  is maintained in the closed position by the pressure of spring  652  forcing, via spring holder  654  and ball  660 , ball  662  into hole  1004 , where ball  662  is pegged behind dowel pin  666 . 
     If the pressure in lubrication system component  640  exceeds a predetermined value, the force exerted on end cap  604  by piston  612  is sufficient to force ball  662  out of hole  1004  and over dowel pin  666 , thereby pushing end cap  604  partly out of main housing  602  as shown in  FIGS. 7 and 9  and into an open position. Dowel pin  666 , which extends though indentation  1102  in end cap  604 , prevents end cap  604  from sliding completely out of main housing  602 . With the end cap partly extending out of main housing  602 , ball  662  is no long positioned over hole  1002  and trapped behind dowel pin  666 . The spring force is thus acting entirely within end cap  604  and not against the dowel pin  666  or main housing  602 , so there is no force tending to return piston  612  to its original position to close the relief passage  630 . 
     An operator can reset the valve to the closed position by pushing end cap  604  back into housing  602 . Pushing end cap  604  will cause the hole  1004  to move behind the dowel pin  664  and ball  662  will drop into the hole  1004 , and then be held in place by the spring force via spring holder  654  and ball  660 , whose force on ball  662  includes a downward component that keeps ball  662  extending into hole  1004 . Although not shown in  FIGS. 6 and 7 , a switch similar to switch  470  can also be used on the embodiments shown in those figures. 
     It will be understood that the invention includes more than one novel aspect. Different embodiments can be constructed for different purposes using any of, or combinations of, the different aspects of the invention, and not all the advantages of the invention are, therefore, necessarily achieved by every embodiment that is within the scope of the attached claims. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, rather than o-rings forming a seal around the piston, the piston could press against a metal or an elastic sealing surface in the closed position. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.