PRIORITY CLAIM AND INCOROPROATION BY REFERENCE

This application claims priority of U.S. Provisional Patent Application 61/539,775 filed September 27, 2011, the content of which is hereby incorporated by reference.

BACKGROUND

Shock attenuators are employed in ultra-high pressure waterjet cutting systems to smooth the unwanted pressure excursions caused by the reciprocating operation of the system's intensifier. These systems are typically operated to pressures in the 90,000 PSI (620,528 kPa) range, with the typical need for a minimum volume of 1.5 liters but a preferred volume of 2 liters to optimize the attenuator's effectiveness. As used herein, the term "waterjet cutting system" shall include abrasivejet cutting systems wherein abrasive is entrained into the waterjet. The most economical design has been to use a heavy walled tubular container with a typical inside diameter of 2.375 inches (6 cm) and wetted area of 29 inches (187 cm) or greater. These parameters yield a 2 liter volume large enough to support a dual intensifier system with up to 100 horsepower (74.5 KW) input. A cylinder with 2.375 inch (6 cm) diameter bore creates approximately 266,000 pounds of force (120 655.57 kg of force) against whatever objects are used to close the ends. This presents a twofold problem: first, the strength requirements due to the straight force loading the closure system and, second, the fatigue loading due to the cycling of the attenuator system, typically 10 to 50 times a day. Existing attenuator systems employ a variety of mechanical closure methods: screw-in end plugs, end plugs held in with transverse retainer pins, multiple studs anchored in the attenuator body, and tie rods extending the length of the attenuator body. At the very high working pressures to which these attenuator systems are subjected, failure of the closures can have devastating consequences. The use of screw-in type closure plugs present design problems which, to overcome, are expensive to manufacture. Improper designs can result, and in fact have resulted, in catastrophic failures of the closure system. An example of a catastrophic failure is where the seal material sealing the closure member to the attenuator body migrates into the thread area, increasing the load on the threads due to the thread's resulting maximum diameter being greater than the original (typically, 2.375 inch (6 cm)) seal diameter. A number of such failures are known to have occurred in the waterjet industry. While these failures have fortunately not resulted in any personnel injuries known to the inventor, structural damage has occurred due, for example, to the impact of the end closure parts with structures such as steel I-beams. The use of six or eight high-strength studs or bolts instead of screw-in type closure plugs has proven to be the most cost- effective configuration, and has been less prone to catastrophic failure. However, there have been failures that resulted, in one case known to the inventor, in the end closure penetrating a twelve meter high roof. Such closures demonstrate through calculations that they can withstand the pressure loading. However fatigue problems, assembly problems and loosening of nuts or bolts can result in the over-loading of two or three of the studs. This damages the studs and causes stress levels in excess of the design limits, creating the possibility of catastrophic failure. The systems can be complex or simple like the multiple bolt type, but they all have potential for catastrophic failure, including failures due to human error. Accordingly, there is a long-felt need for attenuators with closures that are highly reliable, cost-effective to manufacture and which minimize the change for human error during assembly. SUMMARY OF THE INVENTION A shock attenuator capable for use with a high pressure fluid line at pressures experienced by waterjet cutting systems comprises an attenuator body having an internal generally axially-extending bore extending between end regions, at least one of which is open-ended. An end plug is disposed within the open-ended region of the bore to seal the bore. The end plug has a though-hole for accommodating a fitting in fluid communication between the bore and a high pressure fluid line. A closure assembly retains the end plug within the bore, and includes a first plurality of generally radially-extending tabs extending from the attenuator body and circumferentially disposed about said axis, with each of said tabs of the first plurality being separated from the next tab by a respective gap, and a second plurality of generally radially-extending tabs coupled to the end plug and circumferentially disposed about said axis, with each of said tabs being separated from the next tab of the second plurality by a respective gap. Said second plurality of tabs is positioned for retention by the first plurality of tabs in such a way that the end plug is retained in the bore when subjected to the high pressure from high pressure fluid within the bore. These and further details of the invention will be apparent to those of ordinary skill in the art from reading a description of the preferred embodiment of the invention described below, of which the drawing forms a part. DESCRIPTION OF DRAWING Figure 1 is a longitudinal section drawing of a shock attenuator constructed in accordance with the invention;

Figure 2A is a side elevation view of the right end cap of Figure 1, viewed in the direction 2A-2A illustrated therein;

Figure 2B is a sectional view of the end cap of Figure 2A taken along line 2B-2B therein;

Figure 3 A is a front elevation view of the shock attenuator of Figure 1; and

Figure 3B is a section view of the attenuator taken along line 3B-3B in Figure 3A. Figure 4A is left side elevation view of an alternative preferred plug configuration used in an attenuator constructed in accordance with the invention;

Figure 4B is front elevation view of the plug of Figure 4 A;

Figure 4C is a right side elevation view of the plug of Figures 4A-B;

Figure 5A is a longitudinal section drawing of an alternative preferred embodiment of a shock attenuator body constructed in accordance with the invention;

Figure 5B is a right side elevation view of the attenuator body of Figure 5A; and Figure 6 is a longitudinal sectional view of shock attenuator body of Figures 5A-B with the plug of Figures 4A-C therein DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As will be clear below, there are alternative configurations of a preferred attenuators constructed in accordance with the invention. One alternative will be referred to below as the "external locked" configuration, and the other will be referred to as the "internally locked" configuration. Externally Locked Configuration Figure 1 shows a preferred attenuator body 1 having an internal bore 1A

communicating between opposing ends. Male end plugs 2 are installed at those opposite ends of the body to close the bore. The attenuator body is closed at each end by a respective end cap 4 having a through- hole 4 A through which fluid communication with the bore is enabled via a fitting hereinafter described. The fitting at each end permits the ingress of fluid at one end of the attenuator body (the "inlet") and the egress of fluid at the other end (the "outlet"). It may be noted, and is known to those of ordinary skill in the art, that the fluid does not necessarily flow through the attenuator. The attenuator can be "T-ed" into the high pressure plumbing with the opposite end of the attenuator blocked, so that one end serves as inlet and outlet passage for the fluid as the fluid pressure in the plumbing varies from the desired value. It should accordingly be understood that an attenuator having either configuration is within the scope of the invention, despite the fact that an outlet at the second end is described and illustrated herein. Figure 2A is a side elevation view of the right end cap 4 of Figure 1 viewed in the direction 2A-2A illustrated in Figure 1, while Figure 2B is a sectional view of the end cap of Figure 2 A taken along line 2B-2B therein. Preferably, the left end cap is a mirror image of the right end cap. As shown in Figures 2A and 2B, the end cap 4 has a plurality of circumferentially-spaced, radially-extending tabs 42a-f that extends radially inward from its peripheral region. Adjacent tabs are separated by a respective one of a plurality of circumferentially-spaced notches 43. The tabs are used to inter-engage tabs form on the attenuator body, as best explained with respect to Figures 3A and 3B. Figure 3 A is a front elevation view of the shock attenuator of Figure 1, while Figure 3B is a section view of the attenuator taken along line 3B-3B in Figure 3A. As illustrated in Figure 3A, the attenuator body 1 has a neck 12 of reduced outer diameter adjacent each end region of the attenuator. The neck 12 lies interjacent its respective end region 14 and the main segment of the body. The end region 14 is illustrated in Figure 3B as having a plurality of circumferentially-spaced, radially-extending tabs 16a-f that extend radially outward from the attenuator body. Adjacent tabs 16a-f are separated by a respective one of a plurality of circumferentially-spaced notches 18. The tabs 14a-f are used to inter-engage tabs 42a-f on the cap during assembly of the attenuator, as explained below. In assembling the end caps onto the attenuator, the notches 43 of the end cap are aligned with the tabs 16a-f of the attenuator body as the cap is slid onto the end of the body. The cap is then rotated so that each tab 42a-f of the cap inter-engages the back side of a respective tab 16a-f of the attenuator body to reversibly affix the cap in place and capture a plug 2 within the end region of the bore. This is repeated at the other end of the attenuator as well. Those skilled in the art will recognize that one or more selected tabs can be oversized (or undersized) with respect to the others to match similarly oversized (or undersized) notches through which they fit during the mounting of the cap onto the attenuator body, if one wishes the cap to be placed on the attenuator only in a predetermined orientation. The plug 2 at each end of the attenuator's bore seals the bore. Sealing of the bore is preferably accomplished at each end using a three piece seal which comprises a generally annular plastic seal 3 with a stainless steel anti-extrusion ring 6. Mounted on the seal body between the seal 3 and ring 6 is an o-ring 12 to energize the seal assembly to begin sealing at a low pressure. The end plug 2 is preferably machined with a radial tang to retain the seal 3 on the end plug during operation and service procedures. As illustrated in Figure 1 , the plug 2 has a generally central through-hole through which an accommodated fitting permits the bore to be connected to a high pressure fluid line to allow the ingress or egress of fluid into and out of the bore. Once mounted to the attenuator and rotated to inter-engage the tabs, the rotational position of the end cap relative the body 1 is can be further secured to increase the safety factor by providing two tapped holes, each accepting a screw 9 that passes through the cap to engage a corresponding hole in the body 1. Engagement of the screw with the attenuator body locks the end cap preventing rotation. Two additional tapped holes can be provided for screws 8 to forcing the end plug to its operating, fully extended position. These two tapped holes in the end plug also can be used by a service person to pull the end plug 2 from the cylinder. Other means can be utilized to secure the cap against rotation after mounting on the actuator body without departing from the scope of the invention. For example, and not by way of limitation, an automatic locking device comprising two spring loaded fingers associated with the attenuator body can be used to trap an end cap tab and prevent the end cap from rotating out of the closed position; the structure of such a configuration is analogous to the manner by which the bottom portion of a beach umbrella' s pole is secured to the top portion of the pole with the use of a spring-loaded finger or ball fitting within a hole aligned therewith to prevent separation and/or relative rotation of the two pieces. Those of ordinary skill in the art will recognize that the presence of a very high pressure fluid within the bore of the attenuator will cause the tabs of the end caps to press

longitudinally outwardly against the tabs of the attenuator body, distributing the load over the total surface area of the tab plurality. The end plug is thereby retained in the bore when subjected to the high pressure from high pressure fluid within the bore. As the high pressure fluid presses the plug against the end cap, the plug is retained within the bore by the attenuator body's tabs acting on the end caps' tabs which are, in turn, effectively coupled to the plug via the end caps contact with the plug. The number of tabs need not be the number illustrated, so long as appropriate design specifications are met for the system's working pressure. Internally-Locked Configuration

In the internally-locked configuration, the interlocking tabs are within the attenuator body instead of externally located. Here, as illustrated in Figures 4A-C, a preferred plug 102 is similar to plug 2 (Figure 1), but provided with a head comprising a plurality of

circumferentially-spaced, radially-extending tabs 104 separated by interjacent

circumferentially spaced notches 106. As illustrated in Figures 5A-B, the end regions of the attenuator's internal bore contains a plurality of circumferentially-spaced, radially-inward extending tabs separated by interjacent notches similar in configuration to those described and illustrated with respect to the embodiment of Figures 1-3. Here, the plug is inserted into the bore so that its tabs pass through the notches extending from the wall of the bore through which it passes, and the plug is rotated to interengage its tabs with those associated with the bore. The resulting configuration is illustrated in Figure 6. Because the plug itself not only seals the bore but additionally resists the outwardly- directed high pressure within the bore, the end caps can be a simple cap of planar or other desired shape that merely masks the plug from view while permitting fluid lines to be couple to the bore via fitting extending from the plugs. The plug can be secured against rotation by screws passing though aligned holes in the cap and plug and/or by spring-loaded fingers as previously described. The illustrated configurations result in a shock attenuator and end closure system that are not subject to catastrophic failure due to a personnel procedural error, that have a factor of safety greater than two, and that are relatively easy to manufacture owing to its simplicity of design. To eliminate the possibility of an overload on the closure mechanism, no threaded retainer method is allowed in the interior of the cylinder. Preventing operator procedural error is accomplished by eliminating multiple retainers, making it impossible for retainers to become loose and cause loading of the other retainers beyond design limits. If one or more tabs and their respective receiving-notches are of different sizes, it is impossible for the assembler to insert the end cap in a position where the locking dogs do not engage their receiving holes. Additional safety is added with a lock screw or pawl that must be physically moved to allow the end cap to rotate into a position of disengagement. The resulting attenuator configuration, when configured in accordance with the preferred embodiment, is believed to be characterized by a closure having the high margin of safety needed for applications such as high pressure waterjet systems. The closure system can provide an automatic locking device to prevent accidental opening. A symmetrical design does not pose the possibility of unsymmetrical loading that could cause stresses in the mechanism that could eliminate its ability to retain the end plug in place. Further, the preferred interlocking system with assembly keying prevents improper assembly, and a seal retention tang on the end closure plug prevents the seal from migrating away from the correct operating position. The result is a closure system that is simple in operation yet much more effective and safer than earlier designs. Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as will be defined by appended claims.

I claim