US3277835A

US3277835A - Fluid device

Info

Publication number: US3277835A
Application number: US380785A
Authority: US
Inventors: Gunnar A Wahlmark
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-07-07
Filing date: 1964-07-07
Publication date: 1966-10-11
Anticipated expiration: 1983-10-11
Also published as: CH433017A; GB1017326A; DE1453703A1; SE302889B

Description

Oct. 11, 1966 Filed July 7, 1964 G. A. WAHLMARK 3,27735 FLUID DEVICE 5 Sheets-Sheet l INVENTOR.

Oct. 11, 1966 G. A. WAHLMARK FLUID DEVICE .'3 Sheets-Sheet 2 Filed July 7, 1964 Oct. 11, 1966 G. A. WAHLMARK 3,277,335

FLUID DEVICE s sheets-sheet 5 Filed July '7, 1964 INVENTOR.

United States Patent O 3,277,835 FLUID DEVICE Gunnar A. Wahlmark, Asjogle, Kristdala, Sweden Filed .lluly 7, 1964, Ser. No. 380,785 10 Claims. (Cl. 10S- 162) The present invention relates in general to fluid devices. It deals more particularly with fluid devices of the swash plate type.

Swash plate type fluid devices are, in general, well known. An illustrative variable displacement pump is shown in the applicants co-pending application, Serial No. 838,868, filed September 9, 1959, now Patent No. 3,136,264, entitled, Variable Displacement Fluid Device. It should be understood, however, that fluid devices of this type may embody either fixed or variable displacement constructions, in addition to operating as either pumps or motors.

Most swash plate type fiuid devices employ a cylinder mechanism connected to a swash plate mechanism by a plurality of pistons. The pistons are reciprocable in the cylinder barrel of the cylinder mechanism, which is rotatable against a bearing surface within the casing of the device. In a fixed displacement fluid device, the bearing surface is conventionally formed on a stational bearing plate seated in the casing or housing. In contrast, in a variable displacement fiuid device the bearing surface is conventionally formed on an arcuately movable port block housing or the like. In either case, it is imperative that the cylinder barrel rotate in substantially fluid tight relationship against the bearing surface to assure proper operation of the device.

It is an object of the present invention to provide an improved swash plate type fluid device.

It is another object to provide a new and improved locking arrangement for preventing unseating of the cylinder barrel from optimum bearing relationship against its complementary bearing surface.

It is yet another object to provide a locking arrangement of the aforedescribed character for both fixed and variable displacement pumps or motors.

It is still another object to provide a simple and inexpensive cylinder barrel locking arrangement.

The foregoing and other objects are realized in accord with the present invention by providing a resilient locking ring releasably retained between the periphery of the cylinder barrel and its mounting element. In one aspect of the invention, the locking ring preloads the cylinder barrel against its complementary bearing surface to assure intimate contact of the barrel With the bearing surface at all times. In another aspect of the invention, the locking ring exerts axial pressure on the cylinder barrel only during specific stages of operation of the device and the barrel rotates in virtually frictionless relationship with the ring in normal operation.

The invention, both as to its organization and method of operation, taken with further objects and advantages thereof, will best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIGURE l is a vertical sectional view taken through a variable displacement fluid pump embodying features of the present invention;

FIGURE 2 is a horizontal sectional view taken through the pump illustrated in FIGURE l;

FIGURE 3 is a sectional view taken along line 3-3 of FIGURE 2;

FIGURE 4 is a sectional vieW taken along line 4-4 of FIGURE 1, with parts removed;

FIGURE 5 is an enlarged sectional view of a first form of cylinder barrel locking arrangement embodying features of the present invention; and

FIGURE 6 is an enlarged sectional veiw of a second form of cylinder barrel locking arrangement embodying features of the present invention.

Referring now to the drawings, and particularly to FIGURES l and 2, a variable displacement fluid pump embodying features of the present invention is seen generally at 10. The pump 10 is designed to pump petroleum fuel to a gas turbine engine (not shown) through its inlet port 11 and expels it under pressure through its outlet port 12 in the pump casing 15. The pump 10 is driven by the drive shaft 16 from a suitable power take-off in the turbine engine.

The casing of the pump 10 comprises a generally cylindrical body 20 closed at one end 21 and having an end cap 22 secured by bolts 24 over its open end 25. An O-ring seal 26 suitably disposed between the cap 22 and the open end of the body 20 provides a uid tight seal therebetween. The body 20 and the cap 22 are preferably formed of a hardened alloy steel.

The inlet port 11 communicates with the interior of the casing 15 via the inlet passage 27 through the closed end 21 of the body 2f). A corresponding outlet passage 28 connects the outlet port 12 with the interior of the casing 15 through the closed end 21. A port cap 30 is mounted flush against the closed end 21 of the body 20 and fixed in position on the closed end by a series of pins 31 (only one of which is shown). An arcuate bearing surface 32 is formed on the inside of the cap for slidably seating the cylinder mechanism 33 of the pump 10.

The cylinder mechanism 33 includes a port block housing 4t) which is slidable on the arcuate bearing surface 32 of the cap 30. A cylinder assembly 41 is seated in the housing for rotation about a cylinder axis pin 43. The port block housing 40 is generally cup-shaped in configuration and is also preferably formed of a hardened alloy steel.

The axis pin 43 extends through a complementary cylindrical aperture 47 in the base 48 of the housing 40 and is necked down at its outer end 49 to slide in the arcuate track 50 formed in the center of the arcuate bearing surface 32 on the port cap 30. The necked down end 49 of the pin 43 is retained in the track 50 by a laterally extending lip 5.1 on the pin Iwhich slides in a complementarily formed lateral recess 52 in the track.

The base 48 of the port block housing 40 includes an arcuate face portion 53 which actually slides against the bearing surface 32, and an adjacent flat face portion 54.

As will be noted, the pin 43 extends approximately through the center of the flat face portions 54 into the track S0. Bracketing the pin 43 in the base 48 and extending therethrough are a fluid inlet, passage 55 and a fluid outlet passage 56. The outer end section of each passage 55 and 56 is enlarged, as at 58, and seats a port shoe assembly 59. Since the port shoe assemblies 59 and corresponding receiving end sections 58 of the passages 55 and 56 are identical, corresponding components of each are identified by corresponding reference numerals.

Each port shoe assembly 59 comprises a vertically elongated port shoe block 61 having passage means 62 extending therethrough. The passage means 62 through each shoe block 61 is elongated sufiiciently to be in constant communication with a corresponding passage 65 through the port cap 30 regardless of the displacement setting of the variable displacement pump 10. O-ring seals 66 assure fiuid tight communication between the inlet passage 27 and the outlet passage 28, extending through the closed body end 21, and corresponding port cap passages 65.

Each port shoe block 61 has an arcuate outer surface 67 which is urged against the complementary arcuate bearing surface 32 on the port cap 30 by a plurality of coil springs 71 seated in suitably formed wells 72 in the housing base 48. The springs 71 bear against a corresponding washer member 73 underlying each port shoe block 61 Suitable sealing elements 74 encircle each port shoe block 61.

Seated against the inner surface 75 of the base 48 in the port block housing is a circular bearing plate 76 which is fixed against movement on the surface 75 by a series of pins 77 (only one shown). The bearing plate 76 is pierced by a conventional kidney shaped inlet port 78 and an oppositely disposed kidney shaped outlet port 79. The cylinder assembly 41 is mounted for rotation in bearing relationship against the outer bearing surface 80 of the plate 76.

As seen in FIGURE 2, the axis pin 43 extends through an axially disposed aperture 81 in the bearing plate 76.

The pin 43 has a transversely disposed key 82 extending through a suitably formed aperture in its mid-section; the key seating in key slots 83 radiating from the aperture 81 to obviate any tendency in the pin 43 to rotate and bind in its track 50 during operation of the pump 10. Fluid is transmitted through the pin 43 for lubrication purposes in the pump through an axial lubrication passage 84 extending the length of the pin 43 and terminating adjacent the track 50 in a lateral lubrication passage 85.

The cylinder assembly 41 includes a cylinder barrel 90 having a bearing face 91 seated in bearing relationship on the bearing surface 80 of the plate 76. The cylinder barrel 90 has an axially disposed bore 92 extending through it which receives the pin 43 in bearing relationship so that the cylinder barrel is fixed for rotation about the axis 93 of the pin 43.

The cylinder barrel 90 is universally connected to the swash mechanism 95 of the pump 10 by pistons 96 reciprocable in cylinders 97 formed in the barrel and a constant speed gear joint 98. Rotation of the swash mechanism 95 by the drive shaft 16 consequently effects synchronized rotation of the cylinder barrel 90 in the housing 48, at a constant speed.

The swash mechanism 95 rotates the cylinder barrel in a clockwise direction (as viewed in FIGURES 3 and 4). As it does so, the piston heads 100 of the pistons 96 are introduced to and withdrawn from corresponding cylinders 97 in a well known manner. Fuel is drawn into each cylinder 97 through its conventional cylinder port 101 from the pump inlet port 11 as the corresponding cylinder 97 moves through 180 from top dead center, as seen in FIGURE l, to bottom dead center. The fuel is then expelled through the same cylinder port 101 to the pump outlet port 12 as the same cylinder 97 moves through 180 from bottom dead center to top dead center.

As the pump 10 operates in this manner, a certain amount of fluid under pressure leaks from the cylinders 97 between the bearing surface 80 on the plate 76 and the bearing face 91 on the barrel 90. This leakage provides lubrication for the rotating barrel 90. At the same time, however, leakage pressure tends to urge the cylinder barrel 90 away from the bearing plate 76. During normal operation of the pump 10, however, operating pressure in the cylinders 97 is effective on the pressure responsive areas 102 adjacent the cylinder ports 101 within the cylinders to create a pressure unbalance effect on the cylinder barrel 90 in the direction of the bearing plate 76 and hold it against the plate. Accordingly, leakage is not a significant factor during normal operation.

This optimum pressure unbalance is not effective during starting and initial operation of the pump 10, however. At such time there is a tendency for the cylinder barrel 90 to unseat from the bearing surface 90 on the plate 76 and allow a heavier film of fluid under pressure to be interposed between the bearing surface 80 and the bearing face 91. Excessive leakage subsequently occurs if such unseating is permitted.

In addition, when rapid changes of displacement of the pump 10 are effected by the displacement control system 105 during operation of the pump, the gyroscopically rotating cylinder barrel 94 tends to precess and thus seeks to effect an unseating of the cylinder barrel from the bearing plate 76. In this light, the displacement control system varies the angular relationship of the cylinder mechanism 33 to the swash mechanism 95 in a wellknown manner. Since it forms no specific part of the present invention, a detailed description of the displacement control system 105 is not thought to be necessary.

The aforedescribed unseating tendencies of the cylinder barrel 90 are prevented in the pump 10 by locking the cylinder barrel for rotation against the bearing plate 76 according to the present invention. A first form of cylinder barrel locking arrangement embodying features of the present invention is illustrated in FIGURES 1-5 and includes an annular frusto-conical abutment surface 111 on the abutment 112 formed from the inside of the skirt 113 of the cup-shaped housing 40. The cylinder barrel 90 rotates freely within the confines of the abutment 112 and has an annular channel 116 formed in its periphery in axial registry with the abutment surface 111.

Seated on the frusto conical abutment surface 111 so that it extends radially into the annular channel 116 in the barrel 90 is a locking ring 120. The locking ring 120 is preferably fabricated of an alloy steel and has a frusto-conical outer surface 121 formed on its periphery and complementary with the frusto-conical abutment surface 111. The locking ring 120 is split so as to define opposed free ends 122, as seen in FIGURE 3, and the uncompressed outside diameter of its frusto-conical surface 121 is slightly greater than the inside diameter of the frusto-conical abutment surface 111. Accordingly, the natural resiliency of the alloy steel ring 120 causes it to ride inwardly of the housing 48 on the frusto-conical surface 111 in the direction of the bearing plate 76.

The effect of the foregoing is to urge the annular planar upper surface 125 on the ring 120 into engagement with the complementary annular planar shoulder surface 126 in the channel 116. Thus, the locking ring 120, which is compressed slightly when it is initially seated on the frusto-conical surface 111, constantly biases the cylinder barrel 90 into engagement with the bearing plate 76.

The ring 120 is snapped into the position illustrated in FIGURE l, for example, by compressing it radially and forcing it past the abutment 112 from the open end of the housing 40. To this end, complementary annular bevelled surfaces 130 and 131 are formed on the ring 120 and the abutment 112, respectively. The ring 120 is sprung past the abutment 112 while already seated in the channel 116 of the cylinder barrel 90, thus locking the cylinder barrel 90 into place.

The split ring 120 is prevented from rotating with the cylinder barrel 90 by a pin 135 removably seated in a suitably formed aperture 136 extending through the skirt 113 of the housing 40 between the opposed ends 122 of the ring (see FIGURE 3). It will thus be seen that the opposed annular planar surface 125 and 126 on the ring 120 and in the channel 116, respectively, slide relative to each other in bearing relationship as the cylinder barrel 90 rotates. The bearing surfaces 125 and 126 are lubricated by the fluid being pumped through the slight leakage hereinbefore referred to and the effect of centrifugal force upon it. Friction between the locking ring 120 and the cylinder barrel 90 is thus kept at a minimum.

The positioning pin is of a diameter which permits only a prescribed amount of radial compression of the ring 120 before the ends 122 of the ring engage the pin. Accordingly, regardless of the force exerted on the ring by the cylinder barrel 90 attempting to unseat itself from the bearing plate 76, the ring 120 compresses only to that point wherein its free ends 122 contact the positioning pin 135, and then the cylinder barrel 90 can force it outwardly no further. Unseating of the cylinder barrel 911 beyond a prescribed limit is thus prevented.

To permit removal of the cylinder barrel 90 from the housing 4.0, a series of three access ports 140 are formed in the skirt 113 on the housing 48 in axial registry with the locking ring 120, as seen in FIGURE 3. By inserting any suitable tools through each of the access ports 140, the ring 120 can be compressed inwardly in the channel 116 and the cylinder barrel 90 drawn freely out of the housing 40. The positioning pin 135 must be removed in such case, of course. In this manner, simple mounting and removal of the cylinder barrel 90 is readily facilitated.

Referring now to FIGURE 6, a second form of cylinder barrel locking arrangement embodying features of the present invention is illustrated .generally at 210. The locking arrangement 210 is identical to the cylinder barrel locking arrangement `111) hereinbefore discussed with but one significant exception. The locking ring 220 of the locking arrangement 210 is constructed so that the outside diameter of its frusto-conical outer surface 221 is slightly less than that of the corresponding surface 121 in the locking arrangement 1111. Accordingly, the frusto conical surface 221 seats on the annular frustoconical surface 111 formed within the skirt 113 of the housing 4t) in radially uncompressed relationship and does not constantly urge the cylinder barrel 90 into bearing relationship with the bearing plate 76. In practice, a space of about .001 inch in width, as at 224, is normally left between the upper surface 225 on the ring 220 and the upper shoulder surface 126 in the channel 116.

Because the locking ring 22@ is not constantly urged into engagement with the cylinder barrel 90, the cylinder barrel 90 rotates in substantial frictionless relationship with the locking ring 221D. Nevertheless, the barrel 91B cannot move more than approximately .001 inch from the bearing plate 76 before it engages the locking ring 2211 and any subsequent or additional tendency to unseat on the part of the barrel 90 is opposed by the resilience of the ring 220.

It should now be seen that with either form of locking arrangement (110 or 210) embodying features of the present invention, unseating of the cylinder barrel 90 from the bearing surface on the plate 76 is first resiliently opposed and, collaterally, prevented. The tendency for the barrel 91D to unseat and permit substantial fiuid leakage from the cylinders 97 is significant during starting of the pump and when rapid changes of displacement are effected by the displacement control system 105, as has been pointed out. Regardless of causation, however, the present invention obviates the effect of any unseating tendency.

In the operation of the pump 10, it has been pointed out that the cylinder barrel 90 is rotated by the swash mechanism 95 through the pistons 96 and the constant speed gear joint 98. At the same time, the cup-shaped housing 40 of the cylinder mechanism 33 is seated for pivotal movement against a retaining ring 150 overlying the swash mechanism 95.

The retaining ring 150 overlies the swash plate 151 which is formed of a relatively stiff bronze such as Muler 600 or the like. The swash plate 151 is mounted in thrust bearing relationship on a Teflon disc bearing 152 seated in the end cap 22 of the pump casing 15. The neck 153 of the swash plate 151 has a shaft receiving bore 154 axially formed therein, and is splined at 155 to receive the correspondingly splined drive shaft 16. A face seal assembly 159 prevents loss of fiuid from the interior of the casing 15.

Three slipper bearings 165 are seated within the cap 22 radially of the swash plate 151, as best seen in FIG- URES 1 and 4. These slipper bearings 165 provide radial bearing surfaces 166 for the peripheral bearing surface 167 on the swash plate 151. The slipper bearings 165 are mounted along one 60 segment of the circumference of the swash plate 151 since radial thrust is effective only in that direction, of course. The slipper bearings are held in place by the retaining ring 150 hereinbefore referred to. The retaining ring 150 is, in turn, held between the cap 122 and the body 2t) of the casing 15.

The swash plate 151 has segmentally spherical recesses 170 formed in its outer surface 171 for receiving the ball ends 172 on the pistons 96. The ball ends 172 are forced into the sockets 170 past the slightly resilient inwardly inclined lips 173 formed from the bronze material of the swash plate 151 around the sockets 170. The lips 173 hold the ball 172 in place in corresponding sockets 170.

The gear-type constant velocity joint 98 hereinbefore referred to includes a ring carrying a plurality of external gear teeth 181 and keyed to the periphery of the swash plate 151, as illustrated. The gear teeth 181 mesh with the internal gear teeth 185 formed in the outer end of a cage 186 secured at its inner end to the periphery of the cylinder barrel 91) by conventional key means. The teeth 181 and 185 are preferably double helical teeth and, consequently, assure constant velocity synchronized rotation of the swash plate 151 and the cylinder 911. Such a gear teeth arrangement is illustrated in Wahlmark Patent No. 3,013,411, entitled, Gear Type Constant Velocity Joint.

It should now be recognized that an improved fiuid device of the swash plate type, incorporating new and improved barrel locking arrangements, has been described and illustrated. Although the swash plate type fiuid device of the present invention is described herein in terms of a variable displacement pump 10, the device might as readily be a fixed placement pump or a fixed or variable displacement motor, as has been pointed out. The cylinder

barrel locking arrangements

110 and 210 embodying features of the present invention are suitably adaptable to all such swash plate type fiuid devices. In this context, however, with a fixed displacement Huid motor or the like, the bearing plate 76 upon which the cylinder barrel 90 rotates in bearing relationship is normally seated against a fixed housing, usually the end of the fiuid motor housing itself.

While several embodiments described herein are at present considered to be preferred, it is understood that various modifications and improvements may be made therein, and it is intended to cover in the appended claims all such modifications and improvements as fall within the true spirit and scope of the invention.

What is desired to be claimed and secured by Letters Patent of the United States is:

1. In a swash plate type fluid device including a swash mechanism operatively connected to a cylinder barrel, wherein the cylinder barrel is normally seated for rotation against the bearing surface provided in housing means, the improvement in barrel locking arrangement comprising: abutment means disposed circumferentially of said barrel in said housing means, shoulder means on the periphery of said barrel in opposed relationship to said abutment means, a locking ring disposed between said `abutment means and shoulder means for preventing unseating of said barrel from properly seated relationship on said bearing surface, said locking ring having a gap formed therein so as to define a split ring, and positioning means extending into said gap for fixing it against rotation with said barrel.

2. The improvement in cylinder barrel locking arrangement of claim 1 further characterized in that said split locking ring is radially resilient and has a frustoconical outer surface formed thereon, and a complementary frusto-conical abutment surface formed on said abutment means, said ring resiliently opposing said unseating of the barrel from the bearing surface.

3. The improvement in cylinder barrel locking arrangement of claim 2 further characterized in that said gap has a first predetermined width, said positioning means being of a second predetermined width less than said first predetermined width whereby resilient radial compression of said ring is limited by said positioning means.

4. In a swash plate type fluid device including a swash mechanism operatively connected to a cylinder barrel, wherein the cylinder barrel is normally seated for rotation against a bearing surface provided in housing means, the `improvement in cylinder barrel locking arrangement comprising: abutment means disposed circumferentially of said barrel in said housing means, shoulder means on the periphery of said barrel in opposed relationship to said abutment means, a split locking ring disposed between said abutment means and said shoulder means for preventing unseating of said barrel from properly seated relationship against the bearing surface, a frustoconical outer surface formed on said ring and a complementary frusto-conical abutment surface formed on said abutment means, whereby said ring is compressed radially by movement of the barrel from the bearing surface.

5. The improvement in cylinder barrel locking arrangement of claim 4 further characterized in that said frustoconical outer surface of said ring has a first predetermined normal diameter, and said complementary frusto-conical abutment surface has a second predetermined diameter, said first predetermined normal diameter being slightly larger than said second predetermined diameter whereby said ring is radially compressed when properly seated between said shoulder means and said abutment means so as to constantly urge said `barrel against the bearing surface.

6. The improvement in cylinder barrel locking arrangement of claim 4 further characterized in that a gap is normally defined between said locking ring and said shoulder means whereby said cylinder barrel rotates freely of said ring in normal operation of the device.

7. In a swash plate type fluid device including a swash mechanism operatively connected to a cylinder barrel, wherein the cylinder barrel is normally seated for rotation against a bearing surface provided in housing means, the improvement in cylinder barrel locking arrangement comprising: an annular abutment formed within said housing means circumferentially of said barrel, a channel formed in the outer periphery of said barrel in axial alignment with said abutment, a radially planar surface defined by said channel, a first frusto-conical inner surface formed on the inner periphery of said abutment, a split locking ring seated in said channel, a first frustoconical outer surface formed on the outer periphery of said ring, and a radially planar surface formed on said ring, said frusto-conical surfaces mating so that said radially planar surfaces are in oppositely disposed relationship whereby any tendency of the barrel to unseat from the bearing surface is opposed by engagement of said `radially planar surfaces and the radial resilience of said ring.

8. The improvement in frusto-conical barrel locking arrangement of claim 7 further characterized by and including a second frusto-conical inner surface formed on the inner periphery of said abutment and a second frustoconical outer surface formed on the outer periphery of said ring, said second frusto-conical surfaces coming into engagement when the barrel is seated in the housing means whereby said ring is initially compressed to permit seating of the barrel against the bearing surface and expansion locking of said ring into an engagement condition between said rst frusto-conical surfaces.

9. In a swash plate type fluid device including a swash mechanism operatively connected to a cylinder barrel, wherein the cylinder barrel is normally seated for rotation against a bearing surface provided in housing means, the improvement in cylinder barrel locking arrangement comprising: abutment means disposed circumferentially of said barrel in said housing means, shoulder means on the periphery of said barrel in opposed relationship to said abutment means, and a radially resilient split locking ring disposed between said abutment means and said shoulder means for preventing unseating of said barrel from properly seated relationship on said bearing surface, said split locking ring having a frusto-conical outer surface formed thereon, and a complementary frusto-conical inner surface formed on said abutment means, said frustoconical surfaces mating to compress said ring and resist unseating of said barrel as said barrel tends to back off from said bearing surface.

10. In .a swash plate type fluid device, housing a means having a bearing surface therein, a cylinder barrel rotatable in seated relationship on said bearing surface, and means for holding said barrel in properly seated relationship on said bearing surface, said holding means consisting solely of abutment means disposed circumferentially of said barrel in said housing means and shoulder means on the periphery of said barrel in opposed relationship to said abut-ment means with a radially resilient snap ring disposed between said abutment means and said shoulder means, said ring being fixed against rotation with said barrel, and opposed frusto-conical surfaces on said ring and one of said abutment means and said shoulder means, whereby said barrel is prevented from departing said properly seated relationship by resilient radial flexing of said ring effected by cooperation between said frusto-conical surfaces as said barrel attempts to back off from said bearing surface.

References Cited by the Examiner UNITED STATES PATENTS 1,817,080 8/1931 Howard 103-162 3,185,105 5/1965 Headings et al 103-162 3,194,172 7/1965 Schottler 103-162 MARK NEWMAN, Primary Examinez'.

SAMUEL LEVINE, Examiner.

R. M. VARGO, Assistant Examiner.

Claims

1. IN A SWASH PLATE TYPE FLUID DEVICE INCLUDING A SWASH MECHANISM OPERATIVELY CONNECTED TO A CYLINDER BARREL, WHEREIN THE CYLINDER BARREL IS NORMALLY SEATED FOR ROTATION AGAINST THE BEARING SURFACE PROVIDED IN HOUSING MEANS, THE IMPROVEMENT IN BARREL LOCKING ARRANGEMENT COMPRISING: ABUTMENT MEANS DISPOSED CIRCUMFERENTIALLY OF SAID BARREL IN SAID HOUSING MEANS, SHOULDER MEANS ON THE PERIPHERY OF SAID BARREL IN OPPOSED RELATIONSHIP TO SAID ABUTMENT MEANS, A LOCKING RING DISPOSED BETWEEN SAID ABUTMENT MEANS AND SHOULDER MEANS FOR PREVENTING UNSEATING OF SAID BARREL FROM PROPERLY SEATED RELATIONSHIP ON SAID BEARING SURFACE, SAID LOCKING RING HAVING A GAP FORMED THEREIN SO AS TO DEFINE A SPLIT RING, AND POSITIONING MEANS DEFINING INTO SAID GAP FOR FIXING IT AGAINST ROTATION WITH SAID BARREL.