Abstract:
A mode shifting apparatus for a decoking tool, a decoking tool and method of operating same. The apparatus includes features to make it rotatably and translationally responsive to changes in pressure of a decoking fluid such that the apparatus is cooperative with the tool and the decoking fluid in a first operating condition to establish a drilling mode with one or more of the tool&#39;s drilling nozzles, and in a second operating condition to establish a cutting mode with one or more of the tool&#39;s cutting nozzles. In one form, the apparatus includes one or more sets of tandem seals disposed along a component interface within the apparatus or between the apparatus and the tool to help redundantly isolate seizure-sensitive components within the apparatus from the pressurized decoking fluid. In another form, the apparatus includes a gas spring to counteract the forces imposed by the pressurized decoking fluid. In another form, the apparatus includes a manual override connection.

Description:
[0001]    This application claims the benefit of the filing date of U.S. Provisional Application No. 61/175,260, filed May 4, 2009. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates generally to tools for removing coke from containers such as coking drums used in oil refining, and more particularly to an enhanced remotely operated cutting mode shifting apparatus for use with a combination decoking tool. 
         [0003]    In conventional petroleum refining operations, crude oil is processed into gasoline, diesel fuel, kerosene, lubricants or the like. It is a common practice to recover heavy residual hydrocarbon byproducts through a thermal cracking process known as delayed coking. In a delayed coker operation, heavy hydrocarbon (oil) is heated to a high temperature (for example, between 900° F. and 1000° F.) in large fired heaters known as fractionation units. The heated oil releases its hydrocarbon vapors (including, among other things, gas, naphtha and gas oils) to the base of the fractionation unit for processing into useful products. The residual is then transferred to cylindrical vessels known as coke drums. These vessels, which are typically configured to operate in pairs, are as large as 30 feet in diameter and 140 feet in height. The combined effect of temperature and retention time leaves this residual, which is known as petroleum coke (or more simply, coke), in a solidified form. This coke residue must be broken up in order to remove it from the vessel, and is preferably accomplished by using a decoking (or coke cutting) tool in conjunction with a decoking fluid, such as high pressure water. 
         [0004]    Such a tool includes a hydraulically-operated drill bit with both drilling and cutting nozzles that are configured to deliver a jet of fluid to the solidified coke. The bit is lowered into the vessel through an opening in the top of the vessel, and is formed into a common tool housing such that the high pressure water supply can be selectively routed through either the drilling or cutting nozzles, depending on the mode of operation. Since high flow rates and pressures (for example, flows of 1000 gallons per minute (gpm) at 3000 to 4000 pounds per square inch (psi)) are typically used for such operations, it is neither practical nor desirable to open drilling and cutting nozzles at the same time. Thus, to achieve this mode shifting, diverter valves or other flow control devices are used to direct the flow to the selected nozzles as required for the decoking operation. There are two commonly used diverter valve designs, both of which are complex, require numerous components, and require a very high level of precision in their manufacture in order to function properly. 
         [0005]    One such valve is a reciprocatable sleeve-type valve having radial ports which selectively align with corresponding ports in the valve body to direct flow to either the drilling or cutting nozzles. The other is a rotatable sleeve, again having ports for selective alignment with corresponding ports of the valve body. In a more benign environment, both designs would provide adequate diversion control and operation. However, the water used in drilling and cutting operations is typically recycled repeatedly, collecting a quantity of suspended coke fines in the process. The passage of this water between seals, sleeves and related slidably-engaged adjacent tool components contributes to localized deposit of the fines. Such deposition can result in component jamming, especially between the sliding components of a reciprocating sleeve-type valve, thereby rendering the valve and the decoking tool inoperative. A similar result may also occur whether the valve is moved by springs, pneumatic or manual means. Once jammed, the tool must be removed, disassembled, and cleaned before decoking can be resumed. In fact, the overwhelming majority of failures in conventional autoshift tools are the result of coke fines entering the autoshift chamber and causing binding in the internal mechanism. 
         [0006]    Another difficulty associated with these earlier designs is that they accomplished their mode shifting upon application of the cutting fluid pressure. Such operation is hard on the components, as the high levels of friction in the adjacent sliding or reciprocating components in such a high pressure environment made relative movement between such components more difficult. Furthermore, in situations involving the introduction of a high pressure fluid into a previously unpressurized (or underpressurized) flowpath, the possibility of a water hammer forming is enhanced. It is additionally problematic in that the already high levels of friction associated with the increasing pressure loads only increased the friction forces arising from the presence of the fines, thereby exacerbating the jamming tendency of the shuttling components. 
         [0007]    A relatively trouble-free, manually shiftable, combination decoking tool was developed and described in U.S. Pat. No. 5,816,505, which is commonly owned by the Assignee of the present invention, and is incorporated herein by reference. The trouble-free nature of this tool is attributable to its mode shifting valve design which includes only a rotatable diverter plate for selectively directing cutting fluid to either pilot hole drilling nozzles or full-width coke cutting nozzles, thus eliminating most of the moving parts associated with other shifting mechanisms. Moreover, because of the simple rotatable flat diverter plate acting on a complementary flat diverter valve body, it also eliminated the multiple interfaces between parts which hitherto provided the jamming and associated failure sites of earlier designs of remotely operated shifting devices. In spite of these improvements, the tool still needed to be removed from the coke drum in order to change the cutting mode. To that end, an automated remotely operating decoking tool, described in U.S. Pat. No. 6,644,567, which is likewise commonly owned by the Assignee of the present invention and is incorporated herein by reference, was developed. The tool disclosed therein extends the operation of the tool disclosed in U.S. Pat. No. 5,816,505 by mounting a shifter body to the decoking tool that can rotate the tool&#39;s diverter plate upon release of the cutting fluid pressure from the tool. It would nevertheless be advantageous to extend the operability of the automated decoking tool disclosed in U.S. Pat. No. 6,644,567. 
       SUMMARY OF THE INVENTION 
       [0008]    In one aspect of the present invention, this advantage is accomplished by providing a remotely operated mode shifting apparatus (also referred to herein as a shifting mechanism) for use with a decoking tool such that the tool can shift between a drilling mode and a cutting mode by rotation of a valving assembly. The apparatus is configured such that upon being connected to a decoking tool, the apparatus is rotatably and translationally responsive to changes in decoking fluid pressure to allow it to switch between drilling and cutting modes. One or more sets of tandem seals are disposed along the interfacial regions that may include a mechanical interface (such as between two or more shafts, journals, bearings or related joined components) or a fluid interface (such as between two or more components that are bathed in a common fluid environment) or other such location formed between components in the shifting mechanism that move relative to one another, as well as between one or more components of the shifting mechanism and the decoking tool that move relative to one another. In the present context, a tandem seal set is made up of two or more seals spaced apart from one another along the surface being sealed in such a way that the second (as well as any subsequent) seal act as a downstream backup to the first or other upstream seal that is exposed to the pressurized fluid. Likewise in the present context, such relative movement will be understood to include one or more of translational and rotational movement. 
         [0009]    The use of such a tandem seal arrangement helps provide redundant isolation of seizure-sensitive components within the apparatus from highly pressurized decoking fluid and the entrained coke fines. In the present context, seizure-sensitive components are understood to be those components used in the mode shifting apparatus that are particularly prone to wear or binding that could lead to apparatus inoperability due to the presence of coke fines in the decoking fluid as discussed above. The inventors have determined that the tandem seals of the present invention are a particularly good way of avoiding the formation of back pressure buildup that may otherwise form to counteract any pressure driving a piston-actuated mechanism or related positive displacement drive motive device, as such a sealing arrangement provides redundancy to reduce the effects of leakage past a single set of lip seals (such as the type commonly used for reciprocating pistons and rotating shafts). The inventors have also determined that the benefits of the present tandem sealing arrangement are especially valuable in situations where the seals are exposed to intermittent pressurization or motion. Because the apparatus of the present invention involves some degree of reciprocal motion of a sealed member, the first of the two sets of seals is exposed to intermittent reciprocation. Likewise, the second of the two seal sets is exposed to intermittent rotation. By separating these two modes of relative movement, the seals can be made more robust than their single set counterparts that must be exposed to both types of movement. As such, the leakage associated with a single set of seals (especially as those seals wear over time) and the concomitant accumulation of incompressible liquid around the mechanical members within the apparatus that can lead to deterioration of performance due to an inability to accommodate the volume displacement of the reciprocating member (such as a piston, discussed in more detail below) due to back pressure can be reduced or avoided. More particularly, this feature of the present invention reduces or eliminates auxiliary connections through which contaminants could enter by using a vented redundant seal arrangement (often referred to as a “double block and bleed” arrangement) to avoid leakage of the pressurized cutting water into the autoshift chamber. 
         [0010]    In optional forms, the decoking fluid flowpath used in the shifting mechanism includes a non-throughflow (or dead-ended) design such that a portion of the decoking fluid that is used to actuate the shifting mechanism enters and exits through the same opening or decoking fluid access port, where the entering is in a first direction and the exiting is in a second direction that is generally opposite of the first direction. In a more particular form, the adjacent components within the apparatus that are moveable relative to one another include at least a drive shaft and an actuating piston. The adjacent components between at least a portion of the shifting mechanism and the tool that are movable relative to one another may in a particular form be a drive shaft and at least one of the apparatus body and a support structure (such as a housing, body, flange or related component) making up a portion of the tool. The drive shaft and the actuating piston may be made selectively and spirally cooperative with one another such that upon changing between the first and second operating conditions, at least one of the drive shaft and the actuating piston moves in at least a translational manner while the other of the drive shaft and the actuating piston moves in at least a rotational manner. In a particular structural configuration, the shifting mechanism is made up of (among other things) a first drive (also referred to as an upper drive) that can be connected to a valve that is used to shift between the drilling and cutting modes of the tool, a second drive (also referred to as a lower drive) that is at least intermittently cooperative with the first drive, and numerous selectively engageable members cooperative with the actuating piston through the second drive such that in a first change of pressurization in the apparatus, one of these members rotates relative to the other, and in a second change of pressurization in the apparatus, both of the members are locked together such that neither rotates relative to each other. In this latter arrangement, the members and the second drive couple with the first drive to force a switch (through the valve) between the drilling and cutting modes in the tool. As will be discussed in more detail below, these selectively engageable members are preferably in the form of rings, which may include detents or related interlocking members. Detents on these selectively engageable rings may be keyed (for example, having one surface sloped and another surface with normal (i.e., perpendicular) facing arrangement between mutually-engageable surfaces) to permit them to be locked together in one rotational movement direction and rotationally decoupled from one another in an opposing rotational movement direction. The apparatus may further include an externally accessible manual override shaft that can be used to change between the drilling and cutting modes by manual adjustment of the shaft. In the present context, the manual override shaft may include a connection in the form of a nut, a milled shaft end, a slotted shaft end, or any other related rotatable extension that can be engaged with a tool and turned. The nut (or other clutching means) is specifically for protecting the internal mechanism against damage from being forced in the wrong direction. 
         [0011]    In another option, a gas spring may be used to oppose a pressurizing force applied by the decoking fluid on the shifting mechanism. In its present form, the spring (not shown) is configured as a translatable piston resident in a complementary-shaped chamber filled with gas. In such configuration, the spring force is directly proportional to the gas pressure so that as the piston is depressed, the gas becomes compressed such that it increases the spring force. Such gas spring may include adjustable features to allow for a wider range of pressure-opposing options than a more fixed traditional spring (such as a coil spring or the like). For example, the amount of gas in the chamber can be introduced into or taken out of the chamber through a fill port (much in the same fashion as a basketball). This is valuable in that it allows for quick changes to the mode shifting apparatus in response to changes in the cutting pressure once the apparatus and tool are mounted in the field. 
         [0012]    In yet another option, vent paths may be formed to allow pressure communication between an ambient environment and an interfacial region between the tandem seals. Such venting allows any pressurized decoking fluid that leaks through the uppermost seal or seals to be routed to the ambient environment rather than across the lowermost seal or seals. The vent paths work particularly well in conjunction with the tandem seals discussed above, as while the tandem seals reduce the likelihood of the pressurized decoking fluid or other liquid from reaching apparatus internals (such as an inner chamber), the vent paths allow pressure relief in the interstitial region between the seals via the unidirectional sealing action of lip seals in the event that such region were to become filled with liquid. 
         [0013]    According to another aspect of the invention, a remotely operated mode shifting apparatus for selectively routing decoking fluid between a cutting nozzle and a drilling nozzle of a fluid jet decoking tool is disclosed. The apparatus includes a body that can be coupled to the decoking tool, a shifting mechanism and a gas spring configured to oppose a pressurizing force applied by the decoking fluid on the shifting mechanism. As with the previous aspect, the shifting mechanism is rotatably and translationally responsive to changes in pressure of a decoking fluid such that in a first operating condition, the apparatus is cooperative with the tool and the decoking fluid to establish a drilling mode with the drilling nozzle, while in a second operating condition, the apparatus is cooperative with the tool and the decoking fluid to establish a cutting mode with the cutting nozzle. The gas spring may be used as a restoring force, and in a more particular form, may be adjustable. In that way, the restoring force spring constant can be tailored to the decoking tool requirements, as well as to changes that may occur as the tool wears or is exposed to a different environment. In another form, the gas spring further includes a dampener such that the gas spring can be self-damping such that it can be used in place of conventional damping oil. Such damping in the spring can be controlled by orifices or related porting inside the spring, much in a manner similar to that in an automotive shock absorber. 
         [0014]    Optionally, the apparatus may include one or more sets of tandem seals that can be used to redundantly isolate one or more seizure-sensitive components within the apparatus from the pressurized decoking fluid in the tool. In addition, a vent path can be formed between an ambient environment and a region fluidly disposed between the tandem seals. Together, the seals and the vent reduce the chance that pressurized fluid (as well as entrained coke fines or other contaminants) will work its way into the shifting mechanism. 
         [0015]    According to still another aspect of the invention, a decoking tool is disclosed. The tool includes a housing that can be coupled to a drill stem or other source of decoking fluid. In addition, the tool includes one or more drilling nozzles and one or more cutting nozzles, as well as flowpaths to deliver pressurized fluid from a source that is fluidly coupled with the tool to the nozzles. The decoking tool also includes a remotely operated mode shifting apparatus that can shift between a drilling mode and a cutting mode. The apparatus is rotatably and translationally responsive to changes in decoking fluid pressure to allow the apparatus to switch between drilling and cutting modes. As discussed above, one or more sets of tandem seals are to promote an improved level of sealing between the pressurized fluid and the shifting apparatus. Such a configuration may, for example, help to reduce the likelihood of damage to the shifting apparatus be providing a redundant impediment to leakage of the pressurized fluid (and suspended coke fines or other particles) into the shifting apparatus. 
         [0016]    Optionally, the means comprises a flow control device such that in a first operating condition, the flow control device fluidly couples the source of decoking fluid to the one or more drilling nozzles, while in a second operating condition, the flow control device fluidly couples the source of decoking fluid to the one or more cutting nozzles. In a more particular form, the flow control device is a valve, such as the aforementioned a diverter valve or related rotationally responsive valve. In another option, the decoking tool includes either or both a gas spring and an atmospheric vent similar to those discussed above in conjunction with a previous aspect of the invention. In a more particular form of the decoking tool, a diverter valve plate responsive to a control rod that in turn is manipulated by the apparatus in response to changes in decoking fluid pressure is included. 
         [0017]    The diverter plate, through selective alignment of cutouts, ports or related valve componentry, includes access to conduit that routes the decoking fluid to one or the other of the drilling and cutting nozzles. In other forms, the apparatus includes more than one set of tandem seals where in an even more particular form, a first of the seal sets is placed at an interface between a rotatable drive shaft and a translational piston or related actuator that forms part of the apparatus, while a second of the seal sets is placed at an interface between the rotatable drive shaft and a stationary support structure that makes up part of either the shifting mechanism or the tool. In an even more particular form, the rotatable drive shaft is of a generally tubular, hollow structure such that other actuating equipment (for example, a piston or related pressure-responsive actuator) can be placed concentrically within the space defined within the drive shaft. In that way, the first of the tandem seal sets is disposed on an inner surface of the rotatable drive shaft, and a second of the tandem seal sets is disposed on an outer surface of the drive shaft. As such, both the inner and outer surfaces have a robust barrier that otherwise may expect to encounter potential pressurized decoking fluid leakage. A vent path may be formed between an ambient environment (such as the atmosphere) and a region fluidly disposed between the first and second seals of the tandem seal set. Likewise, a layer of sacrificial material may be placed between adjacently-facing components where the decoking fluid gets routed. Such a sacrificial layer can be used to avoid undue wear to a portion of the routing means or other such valve members. 
         [0018]    According to yet another aspect of the invention, a method of operating a combination fluid jet decoking tool is disclosed. The method includes configuring the tool to cooperate with a mode shifting apparatus that is automatically responsive to changes in decoking fluid pressure. In this way, the apparatus controls which of a drilling nozzle flowpath and a cutting nozzle flowpath the decoking fluid flows through. The tool includes one or more of a gas spring and tandem seals. The method also include introducing the tool into a decoking vessel and providing the decoking fluid to the tool. 
         [0019]    Optionally, the method further includes adjusting the spring constant of the gas spring. In another option, the method includes manually adjusting the apparatus through a manual override nut such that a combination of rotational and translational movement within the apparatus causes the apparatus to shift between a first operating condition where the apparatus is cooperative with the tool and the decoking fluid to establish a drilling mode and a second operating condition where the apparatus is cooperative with the tool and the decoking fluid to establish a cutting mode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The following detailed description of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
           [0021]      FIG. 1  is a cutaway view of the combination coke cutting tool and mode shifting apparatus employing a rotatable diverter plate according to an aspect of the prior art; 
           [0022]      FIG. 2A  is a detailed sectional view of a remotely operating cutting apparatus according to an aspect of the present invention in its rest state; 
           [0023]      FIG. 2B  is a detailed sectional view of a remotely operating cutting apparatus according to an aspect of the present invention in its energized state; 
           [0024]      FIG. 3  is a schematic view of the remotely operating cutting apparatus integrated into a decoking tool; and 
           [0025]      FIGS. 4 and 5  are schematic views of the ratchet portion in its disengaged and engaged positions, respectively. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Referring first to  FIG. 1 , a prior art decoking tool  1  with protective boring blades or vanes  3  and a mode shifting apparatus  4  installed in the tool  1  is shown. The mode shifting apparatus  4  is made up of numerous components, including a body  4 A, actuator sleeve  4 B, actuator slot  4 C, actuator pin  4 D, spring  4 E, pressurized fluid inlet  4 F, annular hydraulic cylinder  4 G, annular piston  4 H, actuator pin carrier  4 I and a liner sleeve  4 J that surrounds a lower portion  6 B of a control rod  6  that also includes an upper portion  6 A that can be joined together in a splined relationship. The control rod  6  is connected to a hydraulic distribution diversion plate (also called diverter plate)  5  such that when the mode shifting apparatus  4  is activated, either manually or by sequentially pressurizing and de-pressurizing operations from a fluid supply (not shown), the control rod  6  rotates the diverter plate  5 , causing openings formed through the axial dimension thereof to alternately expose fluid delivery conduit  7  and either the drilling nozzles  10  or cutting nozzles  11  to a supply of high pressure fluid (for example, water) being delivered through an inlet pipe or drill stem  9 . In the version depicted in  FIG. 1 , the drilling nozzles  10  are in fluid communication with the pressurized fluid supply in order to direct a generally downward stream of high pressure fluid into the coke (not shown), thereby boring a hole for the rest of the apparatus  4  to follow. The generally planar disk-like shape of the diverter plate  5 , coupled with its rotatable mounting arrangement to control rod  6  permits shifting between a cutting mode and a drilling mode to occur by an intermittent clocking rotation of the diverter plate  5 . The details of the construction and operation of diverter plate  5  will not be repeated herein, suffice to say that such details may be found in commonly-owned U.S. Pat. No. 6,644,567. It will be appreciated by those skilled in the art that the attributes of the present invention do not depend on the circular disk shape of the diverter plate  5 , merely that the features disclosed herein may be used in cooperation with such a device as that of  FIG. 1  to alternately seal off and expose the ports to have one or more be active while one or more other ones are inactive. Similarly, the sealing action does not have to be between two flat surfaces either, as local contact by a contoured surface of the diverter plate  5  or appendage thereof at the rim of the port would accomplish the same effect. 
         [0027]    Because the decoking fluid is delivered under extremely high (for example, 5000 psig or more) pressure, it can impart a significant differential pressure across the diverter plate  5  at the locations where the plate  5  cuts off flow between the drill stem  9  and fluid delivery conduit  7 . This results in forces as high as 40,000 lbf pressing the diverter plate  5  and a diverter body wear plate  8  together, which in turn generates a significant static friction that creates a tendency to resist relative rotation between them. In an automated form, such as that depicted in U.S. Pat. No. 6,644,567, the mode shifting apparatus  4  is designed to shift on de-pressurization because the friction (and concomitantly, the driving force needed to rotate the diverter plate  5 ) decreases over the discrete amount of time required to complete the rotation of the diversion plate  5  once it starts moving. This mode of shifting is preferable to shifting during pressurization, where the increasing pressure could raise the friction to a level that would make relative movement between adjacent components such as the diverter plate  5  and diverter body wear plate  8  difficult, as well as result in increased wear. It is additionally beneficial that the shifting takes place at low flow rates and pressure (typically under 500 psig), to avoid water hammer effects as the diverter plate  5  moves from one set of openings to the other. Despite this, there are still paths for the high pressure decoking fluid to leak into the mode shifting apparatus  4 . For example, a generally horizontal slot formed between the diverter plate  5  and control rod  6  to facilitate ease of rotation between them is susceptible to the introduction of pressurized decoking fluid. Furthermore, a small annular gap exists between the control rod  6  and the remainder of the decoking tool body; this gap extends the length of the control rod  6  from its top (where the aforementioned gap is formed) to its bottom (where it joins with the mode shifting apparatus  4 . Such a gap provides a leakage travel path from the horizontal slot above to the fluid inlet  4 F and the annular hydraulic cylinder  4 G. In addition, the annular construction of piston  4 H is such that a reciprocating piston seal (not shown) is required to act on both an inner diameter and outer diameter sealing surface, thereby providing an increased opportunity for leakage and related failure. 
         [0028]    Referring next to  FIGS. 2A ,  2 B and  3 , detailed sectional views of a mode shifting apparatus  100  according to an aspect of the present invention are shown. Unlike the annular piston  4 H of the device in  FIG. 1 , a solid piston  140  is used. In the annular approach employed in  FIG. 1 , hydraulic cylinder  4 G, annular piston  4 H and actuator pin carrier  4 I cooperate with liner sleeve  4 J that is disposed around the lower control rod  6 B and abuts the bottom of the decoking tool  1  adjacent the drilling nozzles  10  so that a gap is formed between the liner sleeve  4 J and the surrounding apparatus body  4 A to define the annular hydraulic cylinder  4 G for receiving pressurized fluid and the subsequent driving of the piston  4 H downward. Pressurization is accomplished through fluid inlet  4 F that is formed in the top of the liner sleeve  4 J. The annular piston  4 H drives an actuator pin carrier  4 I that is concentrically disposed about the liner sleeve  4 J and lower control rod  6 B and carries one or more radially-projecting actuator pins  4 D. An actuator sleeve  4 B is situated below the liner sleeve  4 J and surrounded by the actuator pin carrier  4 I. Actuator slot  4 C receives the actuator pin  4 D that cooperate together to accomplish the shift; these slots  4 C lie on a spiral path of sleeve  4 J, extending along the periphery of the sleeve  4 J so that for each downward movement (as well as for each upward movement) of the actuator pin carrier  4 I, the sleeve  4 J rotates enough to ensure engagement of pawls or related mechanisms on an associated ratchet device. One or more springs  4 E bias the actuator pin carrier  4 I and annular piston  4 H against the ports formed as part of the fluid inlet  4 F so that throughflow is permitted. The spring force (or spring constant) is fixed by the properties of the spring  4 E, including those due to material choice, wire gauge and coil turn rate. While the annular configuration of piston  4 H of the previous device would make it difficult to achieve the redundant protection afforded by the tandem seals of the present invention, the solid shape of the present design means that only one reciprocating surface need be sealed. 
         [0029]    The apparatus  100  is contained in a housing or body  110  and cover  120 , and is attached to a decoking tool  300  to form the bottom portion thereof. In one form, a flange  310  or related mounting structure formed into a portion of the decoking tool  300  can serve as an interface between it and the apparatus  100 . For example, such interface may be in the form of a sleeve bearing or related surface that provides rotational and related support for a rotatable drive shaft  130  that is used to actuate a diverter plate  320  that makes up a part of decoking tool  300  and is similar to diverter plate  5  of the device of  FIG. 1 . The decoking tool  300  is mounted to a drill stem  400  through which a supply of high pressure water or other decoking fluid is provided. The rotatable drive shaft  130  is made of an upper portion (also referred to as the upper drive)  130 A and a lower portion (also referred to as the lower drive)  130 B into which a straight, generally vertical slot  130 C is formed. The generally tubular cylindrical shape of upper drive  130 A (as shown with particularity in  FIGS. 2A and 2B ) engages a lower surface of flange  310  to can serve as an interface between the decoking tool  300  and the apparatus  100 . For example, such interface may be in the form of a sleeve bearing. The upper drive  130 A is centered in a close clearance area at the top of the diversion body so as to minimize any radial load contribution. As such, the connection provides support for a rotatable drive shaft  130  that is used to actuate a diverter plate  320  that operates in a manner generally similar to diverter plate  5  of the device of  FIG. 1 . 
         [0030]    The drive shaft  130  extends through the apparatus  100  so that the top of the upper portion  130 A is coupled to control rod  106  that drives the rotatable portion  320 A of diverter plate  320 , while both flange  310  and the non-rotatable (i.e., stationary wear plate) portion  320 B of diverter plate  320  remain stationary. As with the connection to the decoking tool  300  discussed above, the rotatable drive shaft  130  can be disposed within a complementary surface in the housing  110 , such as through a sleeve bearing or other well-known rotating connection. A reciprocating hydraulic actuator (in the particular form of a piston  140 ) is generally collinear with the rotatable drive shaft  130  and shuttles along a generally vertical axis A of the apparatus  100  in response to driving forces imparted to respective upper and lower surfaces  142  and  143  of piston  140  from the decoking fluid above and an adjustable gas spring  150  below. As discussed above, the decoking fluid being supplied is preferably pressurized water that can be used for both the drilling and cutting applications, as well as provide the driving force to shift the apparatus  100  between the drilling and cutting modes of operation. It will be appreciated by those skilled in the art that other components (such as some those discussed below) can be used in conjunction with the piston  140  to make up an actuator for the purpose of effecting the diverter plate valving and related mode shifting. Gas spring  150  is shown in its extended state in  FIG. 2A  and in its compressed state in  FIG. 2B , and includes a piston  150 A (which can be shaped in a manner generally similar to that of piston  140  discussed above) fitted within or otherwise cooperative with a gas-isolatable chamber  150 B (shown occupying the space in the lower portion of housing  110 ). 
         [0031]    Details of the components that cooperate to facilitate mode shifting are described next. In general, the mode shifting components permit the apparatus  100  to exist in one of two states that depend on which of the two driving forces (i.e., the decoking fluid or the spring  150 ) acting on piston  140  predominate. In operating conditions where the force due to the decoking fluid is greater, the piston  140  is situated in a vertically downward position and a flowpath is established through the diverter plate  320  for either the cutting or drilling nozzles of the decoking tool  300 . Likewise, in operating conditions where the force due to the spring  150  is greater (such as where the supply of pressurized decoking fluid is shut off), the piston  140  is situated in a vertically upward position, and by a ratcheting or clocking rotational movement of the diverter plate  320 , shifts the flowpath coupling from one of the cutting and drilling modes to the other. This ratcheting movement takes place predominantly in drive shaft  130  (which includes upper drive  130 A, lower drive  130 B and vertical slots  130 C that are formed in an upward extension of the lower drive  130 B), as well as though reciprocating and intermittent rotational movement of the piston  140 . As mentioned above, the spring force of the spring  150  can be adjusted, such as through a user-determined introduction of pressurized gas, such as nitrogen or other suitable fluid. Moreover, its operation can reduce or eliminate the need for damping oil. 
         [0032]    The drive shaft  130  and hydraulic piston  140  are in cooperative arrangement with one another through one or more pins  144  cooperative with or formed in the lower end of the hydraulic piston  140 , where the vertical slots  130 C that are formed in lower drive  130 B accept the pins  144 . In addition, a pair of rings  133  and  134 , the first of which engages in strictly rotational movement and the second of which engages in strictly translational movement, are employed to assist in the aforementioned intermittent rotational movement of the piston  140  when pin  144 , under the upward biasing due to spring  150 , traverses a generally spiral path  144 A (shown with particularity in  FIG. 2A ) formed in an actuator cam  132  that is disposed concentrically around lower drive  130 B and vertical slots  130 C. The rotating ring  133  is keyed to the top of cam  132  as well as the generally vertical slots  130 C that form part of the lower drive  130 B. Directly below the rotating ring  133  is a stationary ring  134  that is constrained from rotating by vertical tabs of a retainer  135  that is secured to the housing  110 . The connection of the pin  144 , piston  140  and complementary slots  130 C, actuator cam  132  and rings  133  and  134  is such that a scissors-like motion is created. 
         [0033]    Referring next to  FIGS. 4 and 5 , a pair of one-way rings  133  and  134  are used to promote the selective ratcheting movement of the drive shaft  130  and attached diverter plate  320 . The cooperation between the rotating ring  133  and the stationary ring  134  is shown, where they engage each other through up to four ramped axial teeth  134 A in the stationary ring and matching slots  133 A in the rotating ring. The connection of the cam  132  to the rotating ring  133  is such that when the cam  132  rotates (due to the force of pin  144  during the downward travel of the piston  140 ), it forces the ring  133  to follow, which because of the inclined engagement of contacting surfaces between the teeth  134 A and slots  133 A, facilitates disengagement of the rotating ring  133  from the stationary ring  134  (which is constrained from rotational movement by the vertically upward projection from retainer  135 ) and turn in one direction only. Upon engagement of the teeth  134 A and slots  133 A, they prevent rotation of the rotating ring  133  in the opposite direction. Spring mechanism  160  (which is shown in  FIGS. 2A and 2B ), presses vertically upwards on the stationary ring  134  to engage the teeth  134 A in the slots  133 A. The slope of the surfaces of disengagement of the teeth  134 A and slots  133 , along with the strength of the spring mechanism  160  determine the torque required to disengage the rotating and stationary rings  133 ,  134 . The present arrangement provides a snap action to this portion of the mechanism when the teeth  134 A reengage; such action provides additional indicia of a secure fit between the rotating and stationary rings  133 ,  134 . The surfaces of engagement of the teeth  134 A and slots  133 A have a locking angle to ensure they remain engaged when torque is applied to the rotating ring  133  in the opposite direction. Generally vertical slots  134 B formed at diametrically-opposed outer surfaces of the stationary ring  134  are used to accept an upper projection of retainer  135 , while a flexural spring  160  that is supported on its lower end by lower drive  130 B exerts a bias against a lower surface of stationary ring  134 . Flexural spring  160 , while shown notionally as a coil in  FIGS. 2A and 2B , is more preferably in the form of a multiple Belleville spring to take better advantage of the limited spatial environment in which it works. 
         [0034]    Referring again to  FIGS. 2A ,  2 B and  3 , during decoking operations, respective cutting or drilling cutouts formed in the two axially-alignable plates  320 A,  320 B of diverter plate  320  can be made to cooperate with one another by rotating plate  320 A to allow the passage of the high pressure decoking fluid from the drill stem  400  to the appropriate set of nozzles  410  or  411 . In this situation, the static pressure formed on the diverter plate  320  from the decoking fluid from above restrains it from rotating solely by friction due to the unbalanced force acting on the rotatable portion  320 A of diverter plate  320 . This unbalanced force is due to one set of the ports formed in the rotatable portion  320 A of diverter plate  320  being blanked off, as pressure formed on the upper side where the diverter plate  320  covers the set of ports, as well as atmospheric pressure on the blanked off port side of the diverter plate  320 , acts to provide the necessary friction. The active ports are pressurized due to the back pressure resulting from flow through the active nozzles set of nozzles  410  or  411  whereas the inactive ports are vented to atmosphere through the inactive set of nozzles  410  or  411 . As such, it is the relative friction between these components that controls the action of the mechanism so that during pressurization, this friction constrains the rotatable portion  320 A of diverter plate  320 , the control rod  106  and drive shaft  130  from rotating. 
         [0035]    The pressure on the tool  100  from the decoking fluid acts on the upper end  142  of the piston  140 , creating a downward force that, when it reaches a level where it exceeds the preload in the gas spring  150 , causes the hydraulic piston  140  to translate downwards. The one or more pins  144  move vertically downward in the path defined by the slot  130 C, which is held stationary by the friction at the diverter plate  320  as discussed above, and acting on the spiral slot of cam  132 , forcing the cam  132  to rotate. Likewise, the connection of the rings  133  and  134  as shown in  FIG. 5  forces the two rings  133 ,  134  to rotate relative to one another. Such translational movement of the piston  140  and rotational movement of the cam  132  and ring  133  continues until such time as the lower surface  143  of the piston  140  comes to rest on a shoulder  131 B in the lower drive  130 B. In one preferable form, the lower plate  320 B acts as a wear plate facingly adjacent the upper plate  320 A. As can be seen by particular reference to  FIG. 3 , the wear plate  320 B acts as a stationary appendage at the upper end of the flange  310  and is configured as a sacrificial surface that can be periodically renewed by resurfacing or replacement when worn, thereby avoiding the need to repair or replace the more intricate flange  310 . During pressurization of the tool  300 , the piston  140  starts to move downward once it overcomes the preload in spring  150 . During this downward movement, ring  133  is able to rotate relative to ring  134  due to pin  144  acting on the spiral slot in the actuating cam  132  and straight slot  130 C in the lower drive  130 B. At this point, friction in diverter plate  320  prevents the drive  130  from rotating because the torque required to turn ring  133  relative to ring  134  is not sufficient to overcome the friction between the stationary wear plate  320 B and the rotating upper plate  320 A. This causes slot  130 C to remain stationary, forcing the actuating cam  132  to rotate relative to drive  130 B. The downward travel of piston  140  is arrested as described above, ensuring rings  133  and  134  stop in the correct index position relative to each other and limiting the degree of compression on spring  150 . 
         [0036]    Referring with particularity to  FIG. 2B , when pressure is removed from the apparatus  100  (such as when the flow of decoking fluid is reduced or removed from the drill stem  400 ), the spring  150  forces the piston  140  upward. Unlike the downward movement discussed above, the rings  133  and  134 , by virtue of the overlapping normal contact of the teeth  134 A and slots  133 A and related resistance to disengagement between them when the rings move in a reverse rotational direction relative to one another, remain coupled together. Thus, the two rings  133  and  134 , which are now coupled directly to both the retainer  135  and the cam  132 , remain rotationally stationary during the upward movement of the piston  140 . The pins  144  again are forced to follow a path set out for them, but his time, the path is determined by the generally spiral path  144 A formed in the now-stationary actuator cam  132  which is constrained against rotation induced by pin  144  in the upward direction due to the locking action between rings  133  and  134 . This movement continues until the piston&#39;s shoulder  141  comes in contact with a lower shoulder  131  of the upper drive  130 A, limiting the piston&#39;s upward travel. In addition, the drive shaft  130  now rotates, as its coupling through the vertical slots  130 C also forces to follow the spiral path of the pins  144 . Lower drive  130 B is initially constrained against rotation because the torque induced by pin  144  acting against track  130 C is insufficient to overcome the counterbalancing pressure induced friction at the diverter plate  320 . As the pressure in tool  300  further decays, the net upward force induced in pin  144  increases due to a reduction in the piston  140  force counterbalancing the force from spring  150 . Simultaneously, the resistive friction at the diverter plate  320  reduces with decaying pressure. When the increase in shaft torque induced by pin  144  reaches a level where it can overcome the reduced friction at diverter plate  320 , shifting motion commences. Since this shifting action starts to take place during decaying pressure and while the force due to friction at diverter plate  320  drops once it starts rotating, the pressure at which the shift mode changes is consistent, and therefore repeatable and well-defined. Furthermore, as discussed above, this is made adjustable by altering the charge pressure of spring  150 . The charge pressure of gas spring  150  affects the amount of water pressure (also known as the setup pressure) that is required to compress the spring  150 , thereby allowing the mechanism to start to shift. 
         [0037]    Spring  150  as discussed above may additionally include damping features that are used to control the rate at which the mechanism moves. As mentioned above, such features can be in the form of a shock absorber integrated into the gas spring  150 . Generally, the damping is kept high enough that changes in the gas spring charging pressure have only a minor effect on the rate of shifting. Although not shown, the chamber  150 B that forms isolatable container with which to hold the pressurizable gas may include features similar to that of an automotive shock absorber, including an inner cylindrical region and an outer cylindrical region connected by one or more internal orifices that can be arranged to control the rate of movement of the gas within the spring. The pressurizable gas (also called a charging medium) may be any conventional (and preferably inert) gas, such as nitrogen. In one form, this gas can be pressurized to a degree necessary to provide adequate damping for apparatus  100 , such as between approximately 200 pounds per square inch and approximately 1500 pounds per square inch such that it produces a maximum piston  150 A travel speed of approximately 20 inches per second that exhibits a precipitous and early drop in travel velocity versus travel distance. Furthermore, the present inventors have determined that the mode shifting apparatus  4  could include torque adjustment to optimize the shifting pressure. 
         [0038]    An important point of this damping feature is that it provides a self contained, maintenance-free way to control the rate of movement within the apparatus  100 . Because the mode shift takes place on decreasing pressure, there is no significant friction at the diverter plate  320  at the interface between stationary and rotating plates  320 A and  320 B to act as a brake once the rotation between them is set into motion. Such lack of frictional resistance means that the apparatus  100  may have a tendency to overrun the correct index position for the next operating mode. Prior attempts at avoiding this situation through mechanical means were unavailing, as they had a tendency to introduce high component stresses, and were otherwise not effective at arresting the momentum associated with diverter plate rotation. The use of the presently-disclosed damping features to limit the acceleration and momentum of the apparatus  100  improves the ability to control its stopping position. The weakness of damping in the pre-existing design is that it uses a liquid in the damping mechanism&#39;s chamber; such liquid is susceptible to being lost (through leakage), over-filling, or contamination from leakage of the cutting fluid through the seals. This in turn necessitated the use of external ports to facilitate maintenance and level control. The very existence of these external ports has proved to be a potential for failure due one or both of contamination from the external environment and poorly executed maintenance. 
         [0039]    In situations where a manual mode change of the apparatus  100  is desired, the tool  100  also can be manually shifted by placing a wrench on an override connection (shown in the form of a shaft)  170  that is situated on an upper portion of the cover  120  and turning it with an appropriate tool. This, in turn, drives a set of bevel gears  180 A and  180 B, one of which is attached to the lower drive  130 B. The snap-action of the spring loaded rings  133 ,  134  discussed above provides the operator a sense of feel for when the tool  100  reaches its next clocked position. The override connection  170  has an indicator mark on it to visually show the position of apparatus  100 . Further, the override connection  170  has a unidirectional clutch to limit the torque that can be applied in the opposite direction of rotation during override. Such unidirectional clutch could be a nut between the override connection  170  and the tool used to turn it. In addition, the mechanism is locked during override by the stepped interface between rings  133  and  134  against reverse rotation. Turning the drive connection  170  backwards results in it unthreading rather than damaging the internal mechanism of the apparatus  100 . 
         [0040]    Note that the piston  140  and drive shafts  130 A,  130 B rotate together as the tool  100  shifts. Therefore, the motion of the piston  140  relative to the drive shaft  130  is strictly reciprocating whereas the motion of drive shaft  130  relative to the body  110  is strictly rotating. The primary output of the mode shifting apparatus  100  is a ninety degree increment of rotary motion through the output drive  130 , which in turn is used to turn diverter plate in a manner generally similar to that of U.S. Pat. Nos. 5,816,505 or 6,644,567. As with those designs, the “dead end” design expels all of the pressurized fluid through the same ports through which the fluid entered, providing a cleaning action which reduces the likelihood that coke fines will accumulate and jam the shifting mechanisms of the tool  100 . As such, with each depressurization of the tool  100 , all the cutting fluid, together with suspended coke fines, that is admitted to the annular cylinder in the previous pressurization is expelled from the cylinder through its entrance ports with no flow-through. 
         [0041]    One attribute of the apparatus  100  is that it includes a non-throughflow (i.e., dead-ended) design that ensures that all of the decoking fluid and the coke fines suspended therein that are used to effect the shifting between the two modes are expelled from the hydraulic cylinder through the same path that the fluid was admitted, thereby preventing accumulation of the fines in the apparatus  100  and the concomitant likelihood of component jamming and related failure due to the suspended fines or other contaminants. 
         [0042]    In addition to the dead-ended design, the apparatus  100  includes a first pair of tandem seals  190 A and  190 B along an outer surface of rotatable drive shaft  130  that contacts body  110  of apparatus  100 , and a second pair of tandem seals  190 C and  190 D that cooperate with an inner surface of rotatable drive shaft  130  and the outer surface of piston  140 . The uppermost seals  190 A and  190 C of each seal pair seals against the pressure of the decoking fluid that is introduced into the apparatus  100  from the decoking tool, whereas the lowermost seals  190 B and  190 D of each seal pair reduces the likelihood that any pressurized fluid that leaks past the uppermost seals  190 A and  190 C will reach the inner area of the body  110 . Seals  190 A and  190 C are situated vertically above seals  190 B and  190 D, while seals  190 A and  190 B are situated radially outward relative to seals  190 C and  190 D. Between each pair of seals (for example, between upper seal  190 C and lower seal  190 D) are a series of radially-extending vent holes  200 A,  200 B to allow the space between the seals to be vented to the atmosphere. In this way, any leakage formed between the tandem seals (whether between the primary outer seal  190 A and the secondary outer seal  190 B or between the primary inner seal  190 C and the secondary inner seal  190 D) will not result in a concomitant pressure buildup, as the preferential path for any such buildup will be through vent holes  200 A and  200 B. Hence the first seals  190 A,  190 C of each pair seals against the pressure of decoking fluid, whereas the second seals  190 B,  190 D of each pair ensures that any leakage getting past the first seals  190 A,  190 C cannot enter the inner area of the body  110  of the apparatus  100 . The tandem seal feature, in conjunction with the use of the gas dampener features of spring  150  avoids unnecessary exposure of the components to the harsh coke cutting environment. As is apparent from the manner of operation of the apparatus  100 , the piston  140  reciprocates relative to the drive shaft  130  during the downward stroke of piston  140  such that there is purely translational relative to the upper drive  130 A of drive shaft  130 . As such, the second pair of tandem seals  190 C and  190 D act to reduce or eliminate leakage of the decoking fluid across the bearing surface or related interface between the piston  140  and the drive shaft  130 . 
         [0043]    The above discussions put emphasis on the tool failing due to pressurized cutting water being present in the shifting mechanism chamber. It is true that having a back pressure on the piston will reduce the force developed, and hence become a performance issue. Pressure aside, however, the presence of an incompressible fluid at the backside of the piston can be an issue, as the piston requires displacement volume to function properly. In the event that an incompressible liquid ever completely filled the shifting mechanism chamber, it could prevent the piston from developing full travel. In prior art configurations, a conventional relief valve was employed to avoid such a scenario. The exposure of such a valve to the outside environment could contribute to a high likelihood of failure, thereby allowing contaminants from the external environment (which may include includes expended cutting water and tailings from the cutting operation) to enter the shifting mechanism chamber and increase the chances of even more severe contamination and seizing of the mechanism than the cutting water alone. The tandem seals  190 A- 190 D (which are all in the form of lip seals) can reduce the chances of this happening through the use of the vented interspace region between radially-extending vent holes  200 A,  200 B that prevents cutting water from reaching the second (i.e., downstream) seal (for example, one or both of seals  190 B and  190 D) under pressure and leaking into other parts of the apparatus  100 . Likewise, this vented interspace (or interstitial) region prevents an undue pressure buildup. Moreover, the vented interspace allows the second lip seal to act as an integral relief valve for the apparatus  100  due to its unidirectional sealing properties. In the present context,  190 A and  190 C are considered primary seals, while  190 B and  190 D are considered secondary seals. The venting site is in a much more protected environment and the manner in which lip seals relieve downstream fluid does not make it prone to allowing solids to migrate into the inner chamber portion of the apparatus  100  during venting. 
         [0044]    While certain representative embodiments and details have been shown for purposes of illustrating the invention, it will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention, which is defined in the appended claims.