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CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a non-provisional application of co-pending U.S. Provisional Application No. 61/860,627 filed on Jul. 31, 2013, the benefit of which is claimed and which incorporated herein in its entirety. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     This invention relates generally to drilling equipment used particularly in the hydrocarbon production industry, and specifically to a spider system and method for running or raising tubulars in a well. 
     2. Background Art 
     In the hydrocarbon production industry, tubular goods, including drill strings, casings and tubing, referred to simply as tubulars, must at varying stages be run, i.e. lowered, into or raised from a well. An elevator is a device that is carried by the drilling rig&#39;s traveling block or a top drive, which supports the tubular for the purpose of raising or lowering it. An elevator may clamp along the side of a tubular using slips and dies to exert a radial clamping force on the tubular wall, or an elevator may use a bushing to support the tubular at the lower lip of a box connector. 
     A spider, much like an elevator, is a device which supports a tubular to prevent it from descending into a well when it is not held by an elevator. Unlike an elevator, however, a spider is designed to remain on the drilling deck and is typically not moved vertically. When the elevator, suspended by the traveling block, nears its high limit of travel (when raising a tubular) or its low limit or travel (when running a tubular), or when a stand is required to be added or removed, the elevator must be repositioned in order to continue the operation. The spider supports the tubular prior to the elevator releasing the tubular. Thus, the tubular is held in place while the elevator is repositioned. Once the elevator carries the tubular at a new location, the spider is disengaged allowing the tubular to freely pass through the spider or for the spider to be moved completely clear of the tubular. 
     Some elevators and spiders used today employ power operated internal mechanisms, e.g., power doors and/or power slips. The powered elevators and spiders are commonly hydraulic, but can be pneumatic or electric. 
     SUMMARY OF THE INVENTION 
     As described herein, exemplary embodiments of the spider described herein are designed for well control scenarios in order to provide a safe method of operating over the well bore. In certain embodiments, the spider sits directly over a rotary table. There are a number of radially disposed dogs controlled by cylinders that extend and retract simultaneously about a tubular or joint of pipe going through the wellbore at the drill floor. When the dogs are extended about the tubular, the spider is operable to support the tubular by the lower lip of a box connector atop the dogs. When the dogs are retracted, the tubulars may be freely run through the spider. 
     When the dogs are extended about the tubular and a tubular connector is set down upon the dogs so as to depress one or more triggers, an interlock in a control system is actuated to prevent movement of the dogs. The triggers are preferably located on or within the dogs. However, even while the spider is thus loaded with a tubular, the dogs may nevertheless be retracted via an emergency override mechanism, which may be located on a remote control panel, for example, thereby allowing the tubular to be dropped into the wellbore. When the tubular has been lifted off of the triggers, the interlock is deactivated, and the dogs of the spider can be operated once again. 
     In certain exemplary embodiments, the triggers may actuate sensor valves located within the dogs. The trigger is depressed when the tubular is landed on it, thereby actuating the sensor valve, which in turn actuates an interlock in the control system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in detail hereinafter on the basis of embodiments represented un the accompanying figures, in which: 
         FIGS. 1A and 1B  are perspective views of a two-piece hinged spider in closed and open positions, respectively, according to an exemplary embodiment of the present invention, showing a central vertical aperture formed therethrough for passage of a tubular and radially arranged dogs operated by hydraulic cylinders; 
         FIGS. 2A and 2B  are plan views of the spider of  FIG. 1A  with dogs in extended and retracted positions, respectively, shown with the top cover plate of one half of the spider removed to reveal dogs and hydraulic cylinders; 
         FIG. 3  is an elevation view of the spider of  FIG. 2B  (shown with the top cover plates of both halves of the spider installed); 
         FIG. 4  is a cross section of the spider of  FIG. 3  taken along section line  4 - 4  of  FIG. 3 , illustrating details of opposing dogs in the retracted position, each including a trigger for detecting the presence of a supported tubular and a sensor valve operated thereby according to an exemplary embodiment of the present invention; 
         FIG. 5  is an enlarged cross section of a portion taken within line  5 - 5  of  FIG. 4 , showing details of the trigger and sensor valve according to an exemplary embodiment of the present invention; 
         FIGS. 6A and 6B  are exploded and assembled perspective views, respectively, of a dog, trigger, sensor valve, and cylinder of  FIGS. 1-5 ; 
         FIG. 7A  is a schematic of a control system of the spider of  FIGS. 1-6B  according to a preferred embodiment of the invention, showing an actuation circuit, and interlock circuit, and emergency retraction circuit in the normal unloaded non-actuated operating state; 
         FIG. 7B  is a schematic of the control system of  FIG. 7A , showing the interlock circuit in a loaded, actuated state so as to prevent operation of the cylinders; 
         FIG. 7C  is a schematic of the control system of  FIG. 7A , showing the emergency retraction circuit in actuated state so as to retract the cylinders regardless of whether or not the spider is carrying a tubular; 
         FIG. 8  is a schematic of a control system of the spider of  FIGS. 1-6B  according to a first alternative embodiment of the invention, showing an actuation circuit, and interlock circuit, and emergency retraction circuit in the normal unloaded non-actuated operating state; and 
         FIG. 9  is a schematic of a control system of the spider of  FIGS. 1-6B  according to a second alternative embodiment of the invention, showing an actuation circuit, and interlock circuit, and emergency retraction circuit in the normal unloaded non-actuated operating state. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the interest of clarity, not all features of an actual implementation or method are described in this specification. Also, the “exemplary” embodiments described herein refer to examples of the present invention. In the development of any such actual embodiment, numerous implementation-specific decisions may be made to achieve specific goals, which may vary from one implementation to another. Such would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. Further aspects and advantages of the various embodiments and related methods of the invention will become apparent from consideration of the following description and drawings. 
     The foregoing disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” “uphole,” “downhole,” “upstream,” “downstream,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the apparatus in use or operation in addition to the orientation depicted in the figures. 
       FIGS. 1A and 1B  illustrate a spider  10  in closed and open positions, respectively, according to an exemplary embodiment of the invention. Spider  10  is formed by a first half  12 A and second half  12 B, which are pivotally connected to one another via a hinge mechanism  14 A. Another hinge mechanism  14 B is positioned opposite hinge mechanism  14 A to thereby secure spider  10  in a closed positioned when desired. When closed, spider  10  has an opening  16  that defines a central axis  18 . During operation, tubulars are extending down through opening  16  to conduct reservoir operations as known to routineers in the art. 
     Spider  10  includes a frame  15  that carries a plurality of dogs  20  radially positioned around opening  16 . Frame  15  may be dimensioned and arranged for spider  10  to be carried atop a rotary table or the like. In certain exemplary embodiments, each dog  20  is coupled to a hydraulic cylinder  22  which actuates (retracts and extends) dog  20  into and out of opening  16  to engage and release the tubulars. Hydraulic cylinders  22  are coupled to and powered by a hydraulic power unit  120  (e.g.,  FIG. 7A ). Upper and lower cover plates  17 ,  19  are attached in the center of frame  15  and provide protection for dogs  10 . One or more triggers  24  and sensor valves  28  are positioned on or within dogs  20  for detection of a tubular carried by the dogs, as described in greater detail below. 
       FIGS. 2A and 2B  are plan views that illustrate spider  10  with dogs  20  in extended and the retracted positions, respectively, according to an exemplary embodiment of the present invention.  FIG. 3  is an elevation view of spider  10 . Referring to  FIGS. 2A-3 , triggers  24  are exposed to a tubular collar when dogs  20  are extended, thus allowing activation of sensor valves  28  as described below. Although two trigger  24 /sensor valve  28  pairs are shown in spider  10  having four dogs  20 , other combinations may be employed as appropriate. For example, each dog  20  may have a trigger  24  and sensor valve  28 . In addition, in certain exemplary embodiments, a pair of dogs  20  may be coupled to one another such that sensor valve  28  on one of the dogs works to prevent only retraction of that pair of dogs  20 . Those ordinarily skilled in the art having the benefit of this disclosure realize any number of dogs, any number of triggers  24 , and any number of sensor valves  28  may be utilized in various combinations. 
       FIG. 4  is a cross section of the spider of  FIG. 3  taken along section line  4 - 4  of  FIG. 3 , and  FIG. 5  is an enlarged cross section of a portion taken within line  5 - 5  of  FIG. 4 .  FIGS. 6A and 6B  are exploded and assembled perspective views, respectively, of a dog  20  with associated trigger  24 , sensor valve  28 , and cylinder  22 . Referring to  FIGS. 4-6B  collectively, the operation of spider  10 , according to a preferred embodiment, is illustrated. 
     Each dog  20  is connected to and selectively reciprocated by actuator  22 , which may by a hydraulic or pneumatic cylinder or electric actuator. In the embodiments illustrated, cylinder  22  is hydraulic. Hydraulic cylinder  22  includes a sealed piston  21  that is slideably disposed therein. Piston  21  is connected to a connecting rod  23 , which is connected to dog  20 . Cylinder  22  includes an expansion actuation port  25  and a retraction actuation port  27  on opposite side of piston  21 , which are fluidly connected to a hydraulic power unit  120  via control system  100  (e.g.,  FIG. 7A ). 
     Trigger  24  is positioned along the upper surface of dog  20  such that it is depressed by a collar of a tubular supported by dog  20  extending out into opening  16 . Sensor valve  28  includes spool or poppet  30  that is actuated up and down in response to movement of trigger  24 . A spring  34  is positioned around spool  30  in order to bias it, and concomitantly trigger  24 , upwardly. 
     In a preferred embodiment, sensor valve  28  is a three-port spool or poppet valve, having an inlet port  31 C, an exhaust port  31 A, and an outlet port  31 B. In its normally unloaded, spring-biased upward position, spool  30  fluidly couples outlet port  31 B with exhaust port  31 A and isolates inlet port  31 C. When spool  30  is actuated in its downward position under the weight of a supported tubular, spool  30  fluidly couples outlet port  31 B with inlet port  31 C and isolates exhaust port  31 A. Sensor valve  28  is fluidly connected to control system  100 ; ports  31 A,  31 B, and  31 C are connected to conduits  32 A,  32 B, and  32 C, respectively. 
       FIG. 7A  is a simplified schematic of a control system  100  of spider  10  according to a preferred embodiment of the invention. Control system  100  may be implemented using hydraulic components, as shown, pneumatic components, analog and/or digital electrical, electronic, and/or optical components, or a combination of such components. For simplicity of illustration, some components, such as redundant devices, accumulators, pressure relief devices, check valves, pressure gauges, vents, drains, orifices, strainers, and isolation valves, are not illustrated. 
     Control system  100  includes a pressurized supply main  110  and a depressurized return main  112 . One or more pumps  120  (only one is shown for simplicity) draws hydraulic fluid from a reservoir  122  and supplies pressured fluid to supply main  110 . A pressure relief valve  124  is located between supply main  110  and return main  112  so as to relieve any excessive pressure in supply main  110 . Control system  100  also includes a cylinder extension line  116  and a cylinder retraction line  118 , which are fluidly coupled to opposite extension and retraction actuation ports  25 ,  27  on each of cylinders  22 . 
     Supply and return mains  110 ,  112  are connected to cylinder extension and retraction lines  116 ,  118  by a master control valve  130 . Master control valve  130  may be a manual- or solenoid-operated four-port three-way spool or poppet valve, for example. Supply main  110  and return main  112  are connected to first and second inlet ports in master control valve  130 . Cylinder extension line  116  and retraction line  118  are connected to first and second outlet ports in master control valve  130 . 
     Extension line  116  includes an interlock valve  132  and an emergency vent valve  134  located between master control valve  130  and cylinders  22 . Similarly, retraction line  118  includes an emergency shuttle valve  140  located between master control valve  130  and cylinders  22 . Master control valve  130  is connected to a first inlet of emergency shuttle valve  140 . Cylinders  22  are connected to the outlet of emergency shuttle valve  140 . 
     A shuttle valve has two inlet ports on opposite ends of a tubular valve body and outlet port located between the inlet ports. A ball or similar valve element is disposed and rolls freely within the valve body and is operative to block one of the two inlet ports. In this manner, a shuttle valve operates to automatically connect the inlet port having the higher pressure to the outlet port. 
     In an embodiment, interlock valve  132  may be a pilot-operated two-port spool or poppet valve that is connected within extension line  116  in the normally open position. When actuated, interlock valve  132  moves to a shut position so as to isolate extension line  116  and thereby fluidly lock and prevent cylinders  22  from being operated. Interlock valve  132  is operated by one or more sensing valves  28 . Preferably, at least two sensing valves  28  are provided for redundancy purposes. As illustrated in  FIG. 7A , a pair of sensing valves  28  may be connected to the pilot of interlock valve  132  using an interlock shuttle valve  142 . 
     Sensing valve  28  may be manually actuated, spring-return three-port spool or poppet valve that in the non-actuated position fluidly connects the pilot of interlock valve  132  to the depressurized return main  112 , via shuttle valve  142  if provided, thereby venting the pilot of interlock valve  132  so that interlock valve  132  is in the normally open position. When actuated under the weight of tubular set down upon it, sensing valve  28  fluidly connects the pressurized supply main  110  to the pilot of interlock valve  132  to actuate interlock valve  132  to the shut position. 
     In an embodiment, emergency vent valve  134  may be a pilot-operated three-port spool or poppet valve that is connected within extension line  116  in the normally-open configuration between its inlet and outlet ports: The inlet port of emergency vent valve  134  is connected to return main  112  at the corresponding outlet port of master control valve  130  via interlock valve  132 , and the outlet port of emergency vent valve  134  is connected to cylinders  22 . An exhaust port of emergency vent valve  134  is coupled return main  112  at the corresponding inlet port of master control valve  130  so that when emergency vent valve  134  is actuated, extension line  118  is exhausted to return main  112  bypassing interlock valve  132  and master control valve  130 . Emergency vent valve  134  is operated by an emergency retraction valve  136 . 
     Emergency retraction valve  136  may be a solenoid or manually actuated three-port spool or poppet valve. Emergency retraction valve  136  has in inlet port that is connected to supply main  110 , and exhaust port that is connected to return main  112 , and an outlet port that is connected to the pilot of emergency vent valve  134  and to the second inlet of emergency shuttle valve  140 . In its normal, non-actuated position, emergency retraction valve  136  fluidly coupled its outlet port to its exhaust port, thereby venting the pilot of emergency vent valve  134 . 
       FIG. 7A  illustrates control system  100  in a normal unloaded state in which a tubular is not set down upon dogs  20  ( FIGS. 1-6B ) and trigger(s)  24 . Operation of control system  100  in this state is as follows: 
     In a deactivated center position, master control valve  130  may isolate supply and return mains  110 ,  112  and extension and retraction lines  116 ,  118  so that cylinders  22  remain fluidly locked in their present position, whatever that might be. Any over-pressurized fluid in supply main  110  is vented to return main  112  via pressure relief valve  124 . 
     In order to extend cylinders  22 , master control valve  130  is positioned to the extend position, which connects supply main  110  to extension line  116  and return main  112  to retraction line  118 . Pressurized fluid flows from supply main  110 , through master control valve  130 , into extension line  116 , through interlock valve  132  and emergency vent valve  134 , and into the extension actuation ports  25  in cylinders  22 . Return fluid from the opposite sides of the pistons  21  in cylinders  22  exits retraction actuation ports  27  and flows within retraction line  118  into emergency shuttle valve  140 . Depending on the position of emergency shuttle valve  140 , the return fluid may continue through retraction line  118  and through master control valve  130  to return main  112 , or it may flow through emergency retraction valve  136  to return main  112 . 
     In order to retract cylinders  22 , master control valve  130  is positioned to the retract position, which connects supply main  110  to retraction line  118  and return main  112  to extension line  116 . Pressurized fluid flows from supply main  110 , through master control valve  130 , into retraction line  118 , through emergency shuttle valve  140 , and into the retraction actuation ports  27  in cylinders  22 . Return fluid from the opposite sides of the pistons  21  in cylinders  22  exits extension ports  25  and flows into extension line  116 , through emergency vent valve  134 , interlock valve  132 , and master control valve  130 , to return main  112 . 
     In another embodiment (not expressly illustrated), control system  100  may be arranged to completely isolate pump  120  from both extension and retraction ports of  25 ,  27  of cylinders  22  when a tubular is set down upon dogs  20  ( FIGS. 1-6B ) and trigger(s)  24 , thereby disabling both retraction and extension of dogs  20  when under load. As such a control system arrangement is within the ordinary skill of a routineer in the art, further details are not provided herein for brevity. 
       FIG. 7B  illustrates control system  100  in a loaded state in which a tubular is set down upon dogs  20  ( FIGS. 1-6B ) and trigger(s)  24 . Sensing valves  28  are actuated, which in turn actuates interlock valve  132 . In this state, regardless of whether or not master control valve is actuated in the extend or retract positions, cylinders  22  are fluidly locked in their present position. Any over-pressurized fluid in supply main  110  is vented to return main  112  via pressure relief valve  124 . 
       FIG. 7C  illustrates control system  100  in an emergency state in which emergency retract valve  136  is actuated. Pressurized fluid from supply main  110  flows through emergency retract valve  136 , which both actuates emergency vent valve  134  and supplies pressurized fluid to the retraction actuation ports  27  of cylinders  22  via emergency shuttle valve  140  and a portion of retraction line  118 . Return fluid from the opposite sides of the pistons  21  in cylinders  22  exits retraction ports  25  and flows into extension line  116 , through emergency vent valve  134 , and directly to return main  112 , thereby retracting cylinders  22 . In this manner, control system  100  allows cylinders  22  to be retracted in an emergency situation regardless of whether sensor valves  28  are unloaded, as shown in  FIG. 7C , or loaded, as shown in  FIG. 7B . 
       FIG. 8  is a schematic of a control system  100 ′ of the spider  10  of  FIGS. 1-6B  according to an alternative embodiment of the invention. Control system  100 ′ of  FIG. 8  is substantially the same as control system  100  of  FIG. 7A , except that interlock shuttle valve  142  is removed, and each sensor valve  28  directly controls the actuation of an associated interlock valve  132 . Interlock valves  132  are connected in series within extension line  116 . 
       FIG. 9  is a schematic of a control system  100 ″ of the spider  10  of  FIGS. 1-6B  according to yet another alternative embodiment of the invention. Control system  100 ″ of  FIG. 9  is substantially the same as control system  100 ′ of  FIG. 8 , except that sensor valves  28  and interlock valves  132  are replaced by sensor valves  28 ′, which are physically located in dogs  20  ( FIGS. 1-6B ) and operated by triggers  24 , but which are directly connected within extension line  116 . Sensor valves  28 ′ may be simple mechanically operated two-port normally open spool or poppet isolation valves. 
     In summary, a spider and a method for vertically supporting a tubular have been described. Embodiments of the spider may generally have: A frame defining a vertical axis therethrough; at least one actuator carried by the frame; a plurality of dogs radially disposed about the vertical axis, the plurality of dogs coupled to the at least one actuator so as to be movable by the at least one actuator between an inward extended position and an outward retracted position, the plurality of dogs arranged so that when in the extended position, a tubular coaxial with the vertical axis may be vertically supported by the plurality of dogs; a first trigger located on a first of the plurality of dogs so that the tubular influences the first trigger from a first state when the tubular is not vertically supported by the plurality of dogs to a second state when the tubular is vertically supported by the plurality of dogs; and a control system operatively coupled between the first trigger and the at least one actuator, the control system including a first selector operative to selectively move the plurality of dogs by the at least one actuator between the extended position and the retracted position when the first trigger is in the first state and to prevent movement of the plurality of dogs by the at least one actuator when the first trigger is in the second state. Embodiments of the method may generally include: Providing a spider with an opening formed therethrough that defines a vertical axis, the spider including at least one actuator and a plurality of dogs radially disposed about the vertical axis and coupled to the at least one actuator so as to be movable between an inward extended position and an outward retracted position; positioning using a first selector the plurality of dogs to the retracted position; running the tubular through the opening; positioning using the first selector the plurality of dogs to the extended position; vertically supporting the tubular by the plurality of dogs; influencing by the vertically supported tubular a first trigger located on a first of the plurality of dogs; and then preventing by the influenced first trigger positioning the plurality of dogs to the retracted position using the first selector. 
     Any of the foregoing embodiments may include any one of the following elements or characteristics, alone or in combination with each other: A second selector operative to selectively move the plurality of dogs by the at least one actuator to the retracted position regardless of whether the trigger is in the first state or the second state; a sensor valve disposed within the first of the plurality of dogs and operatively coupled to the first trigger; a second trigger located on a second of the plurality of dogs so that the tubular influences the second trigger from an unloaded state when the tubular is not vertically supported by the plurality of dogs to a loaded state when the tubular is vertically supported by the plurality of dogs; the control system is operatively coupled between the second trigger and the at least one actuator; the control system is designed and arranged to allow the first selector to selectively move the plurality of dogs by the at least one actuator between the extended position and the retracted position when the first trigger is in the first state and the second trigger is in the unloaded state; the control system is designed and arranged to prevent movement of the plurality of dogs by the at least one actuator when the first trigger is in the second state or the second trigger is in the loaded state; the first and second selectors are valves; a source of pressurized fluid fluidly coupled to an inlet of the first selector, the at least one actuator fluidly coupled to an outlet of the first selector; the sensor valve is fluidly coupled between the first selector and the at least one actuator; the control system is arranged to completely isolate the source of pressurized fluid from the at least one actuator when the first trigger is in the second state; a source of pressurized fluid fluidly coupled to an inlet of the first selector, the at least one actuator fluidly coupled to an outlet of the first selector; an interlock valve fluidly coupled between the first selector and the at least one actuator; the sensor valve is fluidly coupled to the interlock valve so as to open and shut the interlock valve; providing a second selector to selectively move the plurality of dogs by the at least one actuator to the retracted position when the first trigger is influenced by the vertically supported tubular; disposing a sensor valve within the first of the plurality of dog; actuating the sensor valve by the first trigger when the first trigger is influenced by the vertically supported tubular; providing a second trigger located on a second of the plurality of dogs; influencing by the vertically supported tubular the second trigger located on the second of the plurality of dogs; preventing by the influenced second trigger positioning the plurality of dogs to the retracted position using the first selector; allowing by the first and second triggers the first selector to selectively move the plurality of dogs by the at least one actuator between the extended position and the retracted position when the tubular is not vertically supported by the plurality of dogs; preventing movement of the plurality of dogs by the at least one actuator when at least the first trigger or the second trigger is influenced by the vertically supported tubular; the first and second selectors are valves; coupling a source of pressurized fluid to the at least one actuator via the first selector; isolating the source of pressurized fluid from the at least one actuator by the sensor valve when the first trigger is influenced by the vertically supported tubular; coupling a source of pressurized fluid to the at least one actuator via the first selector; and isolating the source of pressurized fluid from the at least one actuator by an interlock valve that is actuated by the sensor valve when the first trigger is influenced by the vertically supported tubular. 
     The Abstract of the disclosure is solely for providing the United States Patent and Trademark Office and the public at large with a way by which to determine quickly from a cursory reading the nature and gist of technical disclosure, and it represents solely one or more embodiments. 
     While various embodiments have been illustrated in detail, the disclosure is not limited to the embodiments shown. Modifications and adaptations of the above embodiments may occur to those skilled in the art. Such modifications and adaptations are in the spirit and scope of the disclosure.

Summary:
A spider and method for supporting a tubular within a well bore. Radial dogs, controlled by cylinders that extend and retract simultaneously, are operable to support the tubular by the lower lip of a box connector. When a tubular connector is set down upon the dogs so as to depress one or more triggers located thereon, an interlock in a control system is actuated to prevent movement of the dogs. However, even while the spider is thus loaded, the dogs may nevertheless be retracted via an emergency override mechanism thereby allowing the tubular to be dropped into the wellbore. When the tubular has been lifted off of the triggers, the interlock is deactivated, and the dogs of the spider can be operated once again. The triggers may actuate sensor valves located within the dogs, which in turn actuates an interlock valve isolating the flow path of the cylinders.