You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates generally to water well apparatus and, more specifically, to a Well Cleaning Method and Apparatus using detonating cord having Additional Reliability and a Longer Shelf Life.  
         [0003]     2. Description of Related Art  
         [0004]     The present invention is an improvement on U.S. Pat. No. 3,721,297 for Method for Cleaning Wells, and on U.S. Pat. No. 4,757,863 for Well Cleaning Method and Apparatus. The &#39;863 patent sought to, and in fact did, resolve several problems associated with the design of the &#39;297 patent. The method and apparatus disclosed by the &#39;863 patent utilized a design that was less costly and less complex than that disclosed in the &#39;297 patent. Furthermore, the device of the &#39;863 patent is compliant with government transportation regulations that prohibit the shipping of armed explosives. As a result of these improvements, the new device met with continuing and widespread success.  
         [0005]     Despite the sustained success of the revised device, as additional experience has been gained with the device and method of the &#39;863 patent, other deficiencies have been recognized. First, it has become desirable to extend the shelf life of the device, so that long periods of storage (either at the supplier or end-point user) will not make the device unreliable. Second, there has been some evidence of non-sequential detonation in adjacent explosive assemblies; while this is not a safety problem, it can reduce the overall effectiveness of the method and device.  
         [0006]     What is needed, therefore, is an improved well cleaning apparatus that has a longer shelf life and more reliably sequential detonation.  
       SUMMARY OF THE INVENTION  
       [0007]     In light of the aforementioned problems associated with the prior devices and methods, it is an object of the present invention to provide a Well Cleaning Method and Apparatus using detonating cord having Additional Reliability and a Longer Shelf Life. The method and apparatus should employ one or more subassembly, each subassembly having a combustible material, means for igniting the combustible material, and one or more high-strength sleeves attached around portions of the combustible material to attenuate the outwardly-directed pressure wave created by ignition of the combustible material. The assemblies should exhibit staggered detonation with the simultaneous application of electrical current to all assemblies. The combustible material should further be modified to add an additional outer impervious layer such that the combustible material exhibits prolonged shelf life and durability.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The objects and features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages, may best be understood by reference to the following description, taken in connection with the accompanying drawings, of which:  
         [0009]      FIG. 1  is a partial cutaway side view of the assembly of the present invention inserted into a well;  
         [0010]      FIG. 2  is a partial side view of the assembly of  FIG. 1 ;  
         [0011]      FIG. 3  is a partial cutaway side view of the intersection between the first and second assemblies depicted in  FIGS. 1 and 2 ;  
         [0012]      FIG. 4  is a side perspective view of an explosion shield of the present invention; and  
         [0013]      FIG. 5  is a partial cutaway side view of a portion of the shield of  FIG. 4 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventor of carrying out his invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the generic principles of the present invention have been defined herein specifically to provide a Well Cleaning Method and Apparatus using detonating cord having Additional Reliability and a Longer Shelf Life.  
         [0015]     As discussed in the &#39;863 patent, the method and apparatus of a preferred embodiment of the present invention employs a simplified, inexpensive apparatus to create a harmonic wave of radially-outwardly-directed gas pressure within a section of well casing. When created under the current method, the gas pressure wave will travel longitudinally along the length of the casing, thereby cleaning plugged perforations in the casing.  
         [0016]     If standard, unmodified detonator cord is used for this application, the power necessary to clean the casing will also be sufficient to cause severe damage to the casing, particularly when the well is aged. Consequently, the method and apparatus of the present invention modifies the pressure wave so as to provide staged, omni-directional, repetitive harmonic gas pressure releases. Specifically, as the pressure wave travels along the length of the casing (or that portion being treated), the explosive force is restricted at various locations along its length by high strength restrictor sleeves. The result is a plurality of pressure impulses along the length of the casing.  
         [0017]     Furthermore, the apparatus is divided into sub-assemblies which are detonated sequentially, further staggering the generated pressure waves. Having summarized the operation of the present invention, we shall now turn to  FIG. 1  to examine the improvements in additional detail.  
         [0018]      FIG. 1  is a partial cutaway side view of the assembly  100  of the present invention inserted into a well. In the interest of clarity, many of the elements of the present invention are essentially the same as those disclosed in the &#39;863 patent discussed above. In order to highlight the differences between that prior design and that of the present invention, elements that are added or modified in this disclosure begin with the number  100  and extend upward from there.  
         [0019]     As depicted, the assembly  100  comprises three sub-assemblies; two of the three of these are numbered separately in  FIGS. 2 and 3 , below. In operation, the assembly  100  is inserted into a well casing  10  by being attached to a cable and weight  98 , and then lowered down. The casing  10  is defined by a tubular wall containing a plurality of perforations or apertures  12  along its length. As the well ages, obstructions  14  tend to collect or otherwise form in the perforations  12 , leading to plugging; when a sufficient number of the perforations  12  become clogged, the well&#39;s specific capacity is reduced (i.e. it&#39;s water production volume). Until the evolution of this invention and its predecessors, the well had to be replaced or re-perforated; now, it can simply be cleaned by creating a specialized pressure wave that forces the obstructions  14  out of the perforations  12 , without damaging the casing  10 .  
         [0020]     Each sub-assembly (see  FIG. 2 ) is formed of insulated flexible tubing sections  102 A,  102 B and  102 C, having (for example) polyvinyl chloride filled with a combustible material having a selected rate of deflagration. As in the &#39;863 patent, it is still preferred to employ a standard detonating explosive known as PETN (Pentaerythiritol Tetranitrate or Pentaerythrite Tetranitrate). In one preferred form, the outside diameter of the tubing sections  102  is approximately between 0.21 and 0.22 inches in diameter and the tubing has an inside diameter sufficient to provide a desired number of grains of explosive, such as for example 20, 30 or 40 or more grains per foot of length, depending upon the amount of power desired.  
         [0021]     Unlike the tubing in the &#39;863 patent, the tubing sections  102  in the present invention are modified to include a second PVC coating (or other compatible material). As a result, the tubing  102  has an inner sheath  106 A,  106 B and  106 C, as well as a second outer sheath  108 A,  108 B and  108 C. This second PVC coating provides added water-proofing characteristics, while further modulating the explosive force at any given point along the entire length of the tubing  102 . Because the tubing  102  is being lowered into a water-filled well casing  10 , in the past, it was possible for a slight nick in the tubing  102  to allow water to seep into and damage the combustible material; the second layer of PVC extruded over the tubing  102  makes the tubing  102  substantially more durable to inhibit such damage. The addition of the second outer sheath adds approximately 0.02 inches to the outer diameter of the tubing sections  102 .  
         [0022]     Similar to the design of the &#39;863 patent, each section of tubing  102  has a plurality of restrictor sleeves  50  encircling it at spaced-apart intervals. These high strength steel “girdles” are crimped onto the flexible tubes  102  in order to hold them in place. As in the &#39;863 patent, the spacing intervals of the sleeves  50  is between two and one-half and twenty-one feet, depending upon the length of each tube section  102 . The sleeves  50  are made of a drawn seamless mild steel tubing, having a wall thickness in the range of about 1/32 to ¼ inches. As in the &#39;863 patent, each sleeve  50  has a length of about four inches.  
         [0023]     The ends of each tubing section  102  is covered and sealed by end covers  40 ; the design and installation method of these covers  40  will be discussed more fully below in connection with  FIG. 3 . Each tubing section  102  further has a detonator cap  60 A,  60 B and  60 C attached to one said end cover  40 , and crimped in place with a connecting sleeve  110 A,  110 C and  110 D, respectively. Just as in the design of the &#39;863 patent, two of the tubing sections ( 102 A and  102 B here) are connected end-to-end, with their respective detonator caps  60  at their respective opposite end.  
         [0024]     A particular difference between this design and that of the previous designs is the addition of a dampener element  104 A between the end covers  40 B and  40 C; the purpose of this new element will be discussed more fully below in connection with  FIG. 3 . The dampener element  104 A and two ends of the tubes  102 A and  102 B are held together by a connecting sleeve  110 B. Alternatively, the dampener element  104 A could be held in place with durable tape or other material. The dampener element  104 A serves to delay or prevent the detonation from one tube  102 A from causing sympathetic or cross detonation in the adjacent tube  102 B (or vice versa, depending upon the order of initiation). By isolating the detonation of the two tubes  102 A and  102 B from one another, the reliability and explosive effectiveness are enhanced over the prior systems.  
         [0025]     The balance of the elements and functionality of the assembly  100  are substantially as described in the &#39;863 patent. Leads at the triggering end of detonator cap  60 B are connected to the other caps  60 , namely, one is connected to a corresponding electrical lead at the closely adjacent triggering end of detonator cap  60 C, and one is connected to the corresponding location on the detonator cap  60 A. The remaining lead from the detonator cap  60 C is connected to ground (such as by connection to the suspension cable); the remaining lead from the detonator cap  60 A is connected to a switchable power source, such that adding power to this lead will cause the caps  60  to detonate.  
         [0026]     The cable, electrical leads and the assembly  100  are all connected together by suitable means, such as by wrapping tape around the group for the full length thereof, thus securely coupling the assembly  100  to the suspending cable. As with the &#39;863 patent, for the purpose of safety in handling and transport, the detonator caps are not electrically or physically connected until the assembly  100  is ready to be lowered into a well casing (i.e. not during shipping or storage).  
         [0027]     To manufacture the assembly  100 , the tubes  102  are first double-extruded (or more layers, if desirable) and cut to the desired length. The restrictor sleeves  50  are then placed in their proper longitudinal positions and crimped in place. Next, the sealing end covers  40  and tube ends are treated with a non-drying sealant material, such as petroleum jelly. This sealing material has proven to further prevent water leakage into the combustible material.  
         [0028]     Once the covers  40  are inserted over the tube ends, they are crimped in place twice. The second crimp provides still further additional waterproofing characteristics to the assembly  100  to prevent moisture damage due to immersion and/or long-term storage. Next, the tube sections  102  are secured to the cable and wire by spiral tape, leaving adjacent ends of the tubes  102  free for subsequent connection of the detonator caps  60 .  
         [0029]     The detonator caps  60  are prepared for handling, storing and transport by securing the connecting sleeves  110  thereto, leaving the free projecting ends of the sleeves  110  open for future connection to the assembly  100  and grounding the detonator caps&#39;  60  two leg wires. The detonator caps  60  and assembly  100  are transported in separate “four G” shipping containers and stored in separate “type two” magazines.  
         [0030]     For installation and operation in a to-be-cleaned well, the detonator caps  60  are assembled in the field, with the arming of the assembly  100  occurring just prior to use, in the arrangement shown in  FIGS. 1 and 2 . After assembly of the three sub-assemblies, the assembly  100  is lowered into the casing  10  by cable until it resides in an area to be cleaned. Electrical power is applied to the cable and electrical activation of the detonator caps  60  occurs simultaneously; the delay times chosen for each specific cap  60 , aided by the dampener element  104 A, will provide sequential ignition of the tubes of combustible material in a selected sequence.  
         [0031]     The detonation of the assembly  100  is essentially the same as discussed at length in the &#39;863 patent, with the additional protective buffer provided by the dampening element  104 A to insure that one tube  102  is not sympathetically- or cross-detonated by another tube  102 .  
         [0032]      FIG. 2  is a partial side view of the assembly  100  of  FIG. 1 . As shown here, each set of tube  102 , restrictor sleeves  50  and end covers  40  are referred to as modified pressure wave generator sub-assemblies  100 A and  100 B ( 100 C is not depicted). As should be apparent, the spacing of the sleeves  50  and end covers  40  (and therefore detonator caps) is variable and depends upon the geometry of the to-be-cleaned section of the well casing. Finally turning to  FIG. 3 , we can examine three of the unique modifications to the &#39;863 design in more detail.  
         [0033]      FIG. 3  is a partial cutaway side view of the intersection between the first and second assemblies  100 A and  100 B depicted in  FIGS. 1 and 2 . As shown, the combustible material  32  is contained within a first layer of extruded PVC, namely, the inner sheath  106 . This inner sheath  106  is then further surrounded by an outer sheath  108  of PVC. It may be desirable in other embodiments that additional sheaths may be provided, and further that other materials having different properties may be used.  
         [0034]     Prior to inserting the end of the tube  102  into an end cover  40 , the tube  102  and/or inner surface of the cover  40  is coated with a suitable non-drying sealant material  116 . In this example, petroleum jelly has been used, but in other versions, different products may be utilized. The sealant  116  is preferably non-drying to prevent the water-tight seal from degrading over time, particularly when the assembly  100  is in storage for prolonged periods. Prior to the addition of this sealant  116 , there was some propensity for a leak to develop in the assembly  100  while in shipping or storage, only to reveal itself once the assembly  100  was immersed in a well casing for use. Since adding the sealant, it has been observed that fewer misfires occur due to liquid penetration into the combustible material  32 ; this translates into substantially longer shelf lives without compromising the reliability of the system.  
         [0035]     Once the end covers  40  and connecting sleeves  110  are assembled, they are now held in place by an end crimp  112  as well as an intermediate crimp  114 . Adding a seond crimp to the prior design has further added additional reliability in the watertight seal created between the tube  102 , the cover  40  and the connecting sleeve  110 , without necessitating additional sealing material or modification of the unassembled parts used in the assemblies  100 .  
         [0036]     Also depicted here is the dampener element  104 A. As discussed above, the element  104 A is inserted between the first and second sub-assemblies  100 A and  100 B, respectively, to prevent the sympathetic or cross detonation of one tube by another tube prematurely. In this embodiment, the element  104 A is a wooden spacer that is inserted between the sub-assemblies  100 A and  1001 B prior to their final assembly. The element  104 A is held in place either by the connecting sleeve  110 B, as shown, or it might be held there by wrapping with the same tape used to secure the assembly  100  to the cable and wires (see  FIG. 1 ). In other versions, the element might be made from some other non-explosive material that provides adequate sacrificial power-absorbing traits. Turning to  FIG. 4 , we can examine another novel and nonobvious improvement of the present invention.  
         [0037]      FIG. 4  is a side perspective view of an explosion shield  118  of the present invention. The shield  118  comprises a generally cylindrically shaped wall  120  having retainer rings  122 A and  122 B at each end. The wall  120  is preferably made from stainless steel screen material. The rings  122  are preferably made from hardened steel approximately 0.75 inches wide and approximately 0.20 inches in thickness. The retaining rings  122  cause the screen material to stay in its cylindrical shape.  
         [0038]      FIG. 5  is a partial cutaway side view of a portion of the shield of  FIG. 4 .  
         [0039]     Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiment can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.

Summary:
A Well Cleaning Method and Apparatus using detonating cord having Additional Reliability and a Longer Shelf Life is disclosed. The method and apparatus employs one or more subassembly, each subassembly having a combustible material, means for igniting the combustible material, and one or more high-strength sleeves attached around portions of the combustible material to attenuate the outwardly-directed pressure wave created by ignition of the combustible material. The assemblies further exhibit staggered detonation with the simultaneous application of electrical current to all assemblies. The combustible material is further modified to add an additional outer impervious layer such that the combustible material exhibits prolonged shelf life and durability.