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RELATED APPLICATIONS 
       [0001]    This application is based on a prior copending provisional application, Ser. No. 61/581,017, filed on Dec. 28, 2011, the benefit of the filing date of which is hereby claimed under 35 U.S.C. §119(e), and is a continuation-in-part of a prior copending application, Ser. No. 12/957,049, filed Nov. 30, 2010, the benefit of the filing date of which is hereby claimed under 35 U.S.C. §120. 
     
    
     BACKGROUND 
       [0002]    Fluid is commonly pumped though tubing inserted into a well to drill or to provide intervention services, such as stimulation or milling of obstructions. Means for pulsing this flow of fluid have been developed for a variety of applications, including mud pulse telemetry, well stimulation, enhanced drilling, and to extend the lateral range of drilling motors or other well intervention tools. For example, commonly assigned U.S. Pat. No. 6,237,701 and U.S. Pat. No. 7,139,219 disclose hydraulic impulse generators incorporating self-piloted poppet valves designed to periodically at least partially interrupt the flow of fluid at the bottom end of the tubing. At least partially interrupting the flow of fluid in this manner leads to an increase in pressure upstream of the valve and a decrease in pressure downstream of the valve. 
         [0003]    Pressure pulsations in the tubing upstream of the bottomhole assembly (BHA) have a variety of beneficial effects. The pulsations can improve the performance of rotary drilling by applying a cyclical mechanical load on the bit and cyclic pressure load on the material being cut. In combination, these loads can enhance cutting. In addition, the pulsating vibrations induced by these tools in the tubing can reduce the friction required to feed the tubing into long deviated wells. 
         [0004]    The valve also generates pressure fluctuations or pulses in the wellbore near the tool. These pressure pulses can enhance chemical placement in the formation and enhance the production of formation fluids such as oil or gas. In addition, these pulses can be employed to generate a signal that can be used for seismic processing. 
         [0005]    The valve designs disclosed in U.S. Pat. Nos. 6,237,701 and 7,139,219 generate a relatively short pressure pulse, which limits both pulse energy and the effectiveness of the pressure pulse. Commonly assigned U.S. patent application Ser. No. 12/957,049 describes an improved apparatus that limits the pressure differential causing the valve to shift from the open to the closed position and incorporates flow restrictions that further limit the shift rate of the valve between the open and closed positions. The apparatus incorporates a spool valve with clearance seals between sliding valve parts. These clearance seals are wear areas, so that the clearance area at the seals may vary during the time that the valve is in service. When the valve is closed, a critical clearance seal area is subject to high differential pressure. Leakage across this clearance seal gap increases the shift speed and reduces the time that the valve stays closed. Close control of this timing is critical for effective operation of the valve. The clearance tolerance range required for acceptable operation is small, and there can be substantial variations in valve performance if the tolerance range is not met. Increased clearance causing increased fluid leakage through the seals is associated with reduced pulse amplitude and duration. Accordingly, it would be desirable to develop a seal that limits leakage in this area of the valve and provides longer pulses, resulting in more uniform pressure profiles. 
         [0006]    Further, it would be desirable to increase the amplitude and duration of pulses produced by a hydraulic pulse valve. It would also be desirable to reduce the variability in the pulse profile caused by clearance variations and wear and to provide a reliable, debris-resistant means for adjusting the timing of the valve, i.e., the time required for the valve to move between the open and closed states. 
       SUMMARY 
       [0007]    This application specifically incorporates herein by reference the disclosures and drawings of each patent application and issued patent identified above or referenced as a related application. 
         [0008]    In consideration of the discussion provided above, an exemplary hydraulic pulse valve has been developed for generating pressure pulses in a conduit in which the hydraulic pulse valve is disposed. The hydraulic pulse valve includes an elongate housing in which is disposed a valve assembly. The valve assembly includes a poppet that is reciprocally movable between a closed position in which it at least partially blocks a pressurized fluid from flowing through a throat of a poppet seat in the valve assembly, and an open position in which the pressurized fluid flows through the throat of the poppet seat. A reciprocating motion of the poppet between the closed position and the open position generates the pressure pulses in the conduit. Also included in the valve assembly is a pilot that is disposed within the poppet and reciprocates between disparate first and second positions to periodically alter fluid communication paths within the valve assembly. Alteration of the fluid communication paths causes the poppet to reciprocate between the closed position and the open position. A sliding seal in the hydraulic pulse valve controls leakage of a pressurized fluid through the valve assembly, preventing the pilot from prematurely shifting between the first position and the second position. Such premature shifting would cause the poppet to move to the open position too quickly, and the sliding seal thereby increases a time during which the poppet remains in the closed position. 
         [0009]    The sliding seal includes a split ring that is actuated by a pressure differential between an inner surface and an outer surface of the split ring. The pressure differential produces a biasing force that causes the inner surface of the split ring to seal around an outer surface of a piston included within the poppet to limit pressurized fluid leakage along the outer surface of the piston where the seal is provided by the split ring. The split ring limits leakage of the pressurized fluid into a cavity defined at least in part by the pilot. As the pilot moves between the first and second positions relative to the split ring, the cavity moves past the split ring, and the split ring then no longer limits leakage of the pressurized fluid into the cavity. 
         [0010]    The valve assembly further includes a spool housing in which the poppet and the pilot are disposed. The spool housing can comprise a stack of components that are clamped together. 
         [0011]    A flow restriction can be provided that comprises a flat recess on a first component disposed adjacent to a flat surface on a second component. The flat recess and the flat surface together define a slit. The slit intersects a flow passage disposed within the valve assembly and limits a rate at which the pressurized fluid flows through the valve assembly to actuate the pilot to shift between the first and second positions. An opening defined by the slit is smaller in dimension than a diameter of the flow passage intersected by the slit, so that particulate matter that is small enough to pass through the slit will not plug the flow passage to prevent the pressurized fluid from flowing through the flow passage. The slit can be formed between a stop ring and a sleeve disposed around the piston. 
         [0012]    The flow passage intersected by the slit can be employed to convey the pressurized fluid to a cavity in which the sliding seal is disposed. In some exemplary embodiments, the slit can be defined in part by a surface of a lower stop ring. In this embodiment, the slit can filter particulates from the pressurized fluid used to actuate the pilot. 
         [0013]    Another aspect of this technology is directed to an exemplary method for generating pressure pulses in a conduit. This method comprises a procedure that is generally consistent with the functions carried out by the components of the hydraulic pulse valve discussed above. 
         [0014]    This Summary has been provided to introduce a few concepts in a simplified form that are further described in detail below in the Description. However, this Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     
    
     
       DRAWINGS 
         [0015]    Various aspects and attendant advantages of one or more exemplary embodiments and modifications thereto will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
           [0016]      FIG. 1A  is a top plan view of an exemplary embodiment of a hydraulic pulse valve that includes a novel split ring shift control, in accord with the following description; 
           [0017]      FIG. 1B  is cross-sectional view of the hydraulic pulse valve, taken along section line A-A of  FIG. 1A ; 
           [0018]      FIGS. 2A ,  2 B, and  2 C are partial cross sectional views of the hydraulic pulse valve, respectively showing a piston used in the valve going down and a pilot of the valve in an upper position (also illustrating an enlarged portion of the figure), a view of the piston down and the pilot in an upper position, and a view of the piston down with the pilot going down; 
           [0019]      FIG. 3  is an isometric view of an exemplary split ring seal used in the valve; 
           [0020]      FIG. 4  is an isometric view of an exemplary split ring seal assembly; 
           [0021]      FIG. 5A  is a cross-sectional view of another exemplary embodiment of the hydraulic pulse valve, illustrating a slit configuration disposed at a lower stop ring; 
           [0022]      FIG. 5B  is a cross-sectional view of another exemplary embodiment of the hydraulic pulse valve, illustrating a different slit configuration formed at the lower stop ring; and 
           [0023]      FIG. 6  is a cross-sectional view of still another exemplary embodiment of the hydraulic pulse valve, illustrating a slit configuration in relation to an upper stop ring that is formed as a single or integral component. 
       
    
    
     DESCRIPTION 
     Figures and Disclosed Embodiments are not Limiting 
       [0024]    Exemplary embodiments are illustrated in referenced Figures of the drawings. It is intended that the embodiments and Figures disclosed herein are to be considered illustrative rather than restrictive. No limitation on the scope of the technology and of the claims that follow is to be imputed to the examples shown in the drawings and discussed herein. Further, it should be understood that any feature of one embodiment disclosed herein can be combined with one or more features of any other embodiment that is disclosed, unless otherwise indicated. 
         [0025]    The operation and configuration of a poppet valve and pilot shift mechanism in a hydraulic pulse valve are described in applicant&#39;s commonly assigned U.S. patent application Ser. No. 12/957,049, which was filed on Nov. 30, 2010. The present application describes the design of an upper stop ring assembly to control the fluid flow that causes the pilot valve to shift between open and closed states, when generating pressure pulses. 
         [0026]      FIG. 1A  shows a top plan view of the hydraulic pulse valve in which the upper stop ring assembly is included, and  FIG. 1B  shows a cross section of the hydraulic pulse valve, as taken along a section line A-A of  FIG. 1A . Referring to  FIG. 1B , a poppet assembly  12  is disposed inside a spool assembly  11 . Spool assembly  11  is in turn, disposed inside a housing assembly  10 . The housing assembly includes an upper adaptor  15 , a housing  16 , and a lower adaptor  17 . Upper adaptor  15  includes inlet threads and seals to connect a fluid passage  41  to a supply tube, and lower adaptor  17  incorporates threads and seals and a fluid passage  48  for fluid connection to downstream components of a bottom hole assembly, such as a motor and mill, or a jetting head. 
         [0027]    Poppet assembly  12  comprises a piston  33  with a poppet  31  attached at its distal end by a nut  32 , and a pilot bushing  34  attached at its proximal end with a nut  35 . The poppet assembly moves up and down inside spool assembly  11 . The spool assembly includes a poppet seat  13 , a lower manifold  23 , a lower stop ring  22 , a sleeve  21 , a female upper stop ring  20 , a male upper stop ring  19 , and an upper manifold  18 . Female upper stop ring  20  limits the upward travel of piston  33 , and lower stop ring  22  limits its downward travel within spool assembly  11 . A clamp ring  14  is threadably engaged with upper adaptor  15  to securely clamp the components of the spool assembly inside the housing. 
         [0028]    A pilot  36  slides inside poppet assembly  12 , between an upper position and a lower position. In  FIG. 1B , the pilot is shown in its upper position, and the poppet assembly is shown in its lower position, with poppet  31  engaged with poppet seat  13  to block fluid flow through the tool. When the valve is opened as poppet  31  moves out of engagement with poppet seat  13 , fluid moves from inlet passage  41  through fluid passages  42 ,  43 ,  44 ,  45 ,  46 , and  47  to an outlet passage  48 . 
         [0029]      FIGS. 2A ,  2 B, and  2 C show a detail of the seal area, with the poppet and pilot in various positions, as the poppet closes and the pilot shifts. Detail area B of  FIG. 1B , which illustrates the split ring seal area, is shown in  FIG. 2A ,  2 B, and  2 C, respectively, as detail B- 1 , B- 2 , and B- 3 . Detail B- 1  in  FIG. 2A  shows piston  33  moving downwardly, with pilot  36  in its upper position. Fluid passage  44  is at a relatively high pressure and is in fluid communication through a slit  49  and a passage  50 , with a cavity  51  that contains a split ring  40 . This split ring is split at reference letter  61 , as shown in  FIG. 3 , so that it can be sprung open and is thus elastomerically biased to form an interference fit around the outer surface of piston  33 . An outer diameter and a distal side of split ring  40  are pressurized by the fluid in cavity  51 , forcing its proximal side to form a seal against an adjacent surface of male upper stop ring  19  and forcing the internal diameter of the split ring to seal against the outer surface of piston  33 . As shown in  FIG. 1B , the proximal side of male upper stop ring  19  forms a distal surface of a cavity  54 , which is at a relatively low pressure, because cavity  54  is in fluid communication through passages  55 ,  56 ,  57 ,  58 ,  59 , and  60 , with a poppet seat discharge passage  47 . Those skilled in the art will recognize that any leakage flow from the distal to the proximal sides of split ring  40  will cause a pressure gradient between the distal and proximal surfaces of the split ring, so that the average pressure in the internal diameter of the seal is always lower than the pressure on the outer diameter of the seal, and the inner diameter is thus forced into contact with the piston, forming an effective sliding seal around the outer surface of piston  33 . 
         [0030]    Split ring  40  is preferably manufactured from a hard, non-abrasive material such as hard steel or coated with hard material or hardened to prevent wear and to reduce friction between the split ring and the surface of piston  33 . The cross-sectional geometry of the split ring may also be varied to improve wear and reduce friction. In particular, the width of the outside surface of the ring and the width of the surface at the inside diameter may be varied to reduce contact pressure. Split ring  40  is provided to prevent pressurized fluid from cavity  51  leaking up though an annular clearance between piston  33  and male upper stop ring  19 , through flow passage  52 , and into cavity  53 . In the absence of the sealing action of split ring  40 , the leakage flow of fluid though the annular clearance would pressurize cavity  53 , which would cause pilot  36  to start to shift position within piston  33  before the poppet attached to piston  33  is closed and would cause the poppet to open too quickly. 
         [0031]      FIG. 2B  shows the pilot and piston configuration when piston  36  is down and poppet  31  is seated on poppet seat  13 . At this point in the operation of the valve, flow passage  52  is moving past split ring  40  toward the configuration shown in  FIG. 2C . As shown in  FIG. 2C , the flow of pressurized fluid is then directed to cavity  53  to cause the pilot to start to shift downwardly (as shown in the orientation of this Figure). 
         [0032]    As shown in detail C of  FIG. 2A , the flow rate of pressurized fluid into cavity  53  (after flow passage  52  has moved past the seal of split ring  40 ) is limited by the flow restriction provided by slit  49  between female upper stop ring  20  and sleeve  21 . As shown in  FIG. 4 , the flow restriction formed by the intersection of passage  50  and slit  49  can be precisely controlled in order to limit the rate at which the pilot shifts. Slit  49  can be formed by grinding a small area from a portion of a distal surface of female upper stop ring  20  that is adjacent to the proximal end of sleeve  21 , as shown in  FIG. 4 . A smaller flow restriction reduces the pilot shift speed and causes the poppet to stay closed longer. The slit opening (i.e., a spacing between the distal surface of female upper stop ring  20  that is ground away and proximal end of sleeve  21 ) is smaller than the diameter of flow passage  50 , so that any particles small enough to enter the slit will not plug flow passage  50 . The slit opening to flow passage  44  is relatively wide and narrow so that the slit acts as a shear screen that excludes large particles. 
         [0033]    Other configurations of the slit opening are possible. For example, the slit may be formed by grinding the proximal end of sleeve  21  instead of the distal surface of female upper stop ring  20 . 
         [0034]    A similar slit and orifice combination can be incorporated into lower stop ring  22  in order to filter particles that enter though this port from the fluid used to actuate the pilot. As shown in  FIG. 5A , the lower stop ring includes a fluid port  50   a  that is in fluid communication with a slit  49   a,  which controls fluid flow into fluid port  50   a  and filters out particulate matter that would otherwise enter fluid port  50   a.  Slit  49   a  is can be formed by grinding or otherwise removing a portion of the contact area between the distal surface of lower stop ring  22  and the proximal surface of manifold  23 . 
         [0035]    As shown in a further alternative exemplary embodiment of  FIG. 5B , a fluid port  50   b  can be provided in fluid communication with slit  49   b,  which is formed on a portion of the contact surface between sleeve  21  and the proximal surface of lower stop ring  22 . Slit  49   b  controls fluid flow into fluid port  50   b  and serves to filter out particulate matter that would otherwise enter the fluid port. An example of how a portion of one or both of these surfaces may be ground to form a slit, such as slit  49   b,  is shown in  FIG. 4 . It will further be understood that multiple passages and slits can be provided to increase the available fluid flow area through the lower stop ring and thereby increase the rate of fluid flow. Also, the lower stop ring can be configured with a split ring (not shown), like split ring  40 , to provide additional fluid flow control in a manner similar to the upper stop ring assembly described above. 
         [0036]    Furthermore, as shown in  FIG. 6 , the upper stop ring assembly can fabricated as a single or integral upper stop ring  62  (i.e., without using male and female upper stop ring components), with a slit  49   c  formed between in the contact area of the distal end of upper stop ring  62  and the proximal surface of manifold  23 . 
         [0037]    Although the concepts disclosed herein have been described in connection with the preferred form of practicing them and modifications thereto, those of ordinary skill in the art will understand that many other modifications can be made thereto within the scope of the claims that follow. Accordingly, it is not intended that the scope of these concepts in any way be limited by the above description, but instead be determined entirely by reference to the claims that follow.

Summary:
A hydraulic pulse valve for use in downhole tools includes a split ring seal to limit the fluid flow available to shift a poppet in the valve from an open position to a closed position. The split ring seal provides relatively long and repeatable pressure pulses, which improve the effectiveness of the hydraulic pulse valve for borehole applications.