US2869945A

US2869945A - Pump

Info

Publication number: US2869945A
Application number: US547434A
Authority: US
Inventors: Virdean R Mattingly
Original assignee: Individual
Current assignee: Individual
Priority date: 1955-11-17
Filing date: 1955-11-17
Publication date: 1959-01-20
Anticipated expiration: 1976-01-20

Description

Jan. 20,- 1959 v. R. MATTINGLY 2,869,945

PUMP

Filed Nov. 1'7, 1955 2 Sheets-Sheet l VMdeafl fr. Ma/f/ny/y INVENTOR.

%,MWW

1959, v. R. MATTINGLY 2,869,945

PUMP

Filed Nov. 17, 1955 2 Sheets-Sheet 2 V/raean Maff/ny/ INVENTOR.

United States Patent PUMP Virdean R. Mattingly, Houston, Tex.

Application November 17, 1955, Serial No. 547,434

11 Claims. (Cl. 309--3) This invention relates to improvements in heavy duty,

high pressure pumps of the class of mud pumps and cement pumps used in the drilling of wells, and refers more particularly to the removable liners therefor, together with the means for holding the liners in place in such pumps and for providing a seal about the liners and about the opening at the cylinder head of such pumps.

In pumps used in this heavy duty service, the drag of the reciprocating piston on the liner imposes a tremendous force on the liner, which alternates in direction corresponding to the piston travel, tending to move the liner along its longitudinal axis; This has posed for many years a real problem in eitecting a seal for sealing the liner and the cap in place because the successful installations have been such as to require that this force be transmitted through the sealing means itself which means that the liner is in efiect floated in place, and the tremendous force imposed upon the liner by the piston reciprocation has to be supported by the packing.

In pumps of this class, the liners frequently require replacement and the packings need frequent tightening. It is important to provide in such pumps for quick performance of these repairs so as to minimize the down time requirement, as otherwise serious damage to wells may be occasioned.

An object of this invention is to provide in pumps of this class a readily removable liner which has a rigid support in a pump so that the thrust on a liner due to the reciprocation of the piston is supported by rigid metal parts having metal-to-metal abutment and in which an externally energized seal is provided between the liner and body, intermediate the liners ends, and also about the cylinder head opening of the pump.

Another object is to provide in pumps of this class for a rigid metal-to-metal support for the liner in which the liner may be quickly and easily removed, together with the seal arrangements, through an opening in the cylinder hfad' cap which is filled by a readily removable holddown p ug.

Another object is to provide a special cap for pump cylinder heads having an opening of a size to readily pass a pump liner, its holddown cage, and the liner and cap packing assemblies with a plug for the cap opening and adjustable means carried by the plug to hold the liner in place.

Another object is to provide a special cap for pump cylinder heads having an opening of a size to readily pass a pump liner, its holddown cage, and the liner'and cap packing assemblies with a plug for the cap opening and adjustable means carried by the plug to hold the liner in place, and an additional adjustable means carried by the plug for tightening the liner and cap packing independ- 'ently of the adjustable holddown means.

Another object is to provide for quick change of the piston, liner, and liner and cap packing assemblies in pumps of this class.

Another object. is to provide a cap for a cylinder head opening composed of a ring adapted to'be secured in "ice j metal-to-metal abutment with a pumpcylinder head and two separately adjustable parts carried by the ring, one providing a metal-to-metal holddown for the liner and the other an independently adjustable packing tightening means.

Another object is to provide a special cap for a pump cylinder opening with means for tightening the cap in rigid metal-to-metal abutment with a pump cylinder head and a removable plug closing the opening in the cap for facilitating quick change of liners, in which the plug is threaded in the cap opening and carries stop means to limit the threading of the plug in the cap so as to provide for pre-stressing of the threads with a threaded holddown stud carried by the plug for holding the liner in place and lock means for pre-stressing the threads of this stud.

Another object is to provide for pumps of this class a liner holddown and seal assembly in which the liner may be fabricated of tubular stock having substantially the same external diameter throughout its length to effect a saving in material cost and fabrication cost.

Other and further objects of the invention will appear from the following description and the drawings. 7

In the drawings which form a part of the instant specification and which show certain illustrative embodiments of the invention:

Fig. l is an end elevational view of a to which this invention relates;

Fig. 2 is a sectional view through one of the pump cylinders of a pump and illustrates one preferred embodiment of a liner and holddown and sealing means therefor associated with this type of pump;

Fig. 3 is somewhat similar to the righthand end of Fig. 2, the remainder of the pump being similar to Fig. 2 but showing a modification for supporting the inner endof the liner which is particularly adaptable for use in new pumps, while the arrangement in Fig. 2 shows the adaptation of this invention to presently existing pumps;

Fig. 4 illustrates another modification for supporting th inner end of a pump liner in accordance with this invention;

Fig. 5 illustrates a different type of pump from that shown in Fig. 2 and is a cross-section through one of the cylinders of the pump showing a modified cap, liner and seal assembly embodying this invention;

Fig. 6 is a view similar to Fig. 5, upon a somewhat enlarged scale to show more detail, and illustrating another embodiment in that the liner is of the type having an external shoulder on its outer periphery for supporting the liner against movement, away from the cylin der head; a

Fig. 7 is a fragmentary showing of the cylinder head and of the pump cylinder shown in Fig. 5 with a modified type of holddown cap; and

Fig. 8 is a fragmentary view upon an enlarged scale showing a modified holddown cap on the type of pump shown in Fig. 2.

Referring to Fig. 1 of the drawings, a pump is shown in rough outline with the inlet for pumped fluid shown at 10 and the outlet, equipped with a dampener, shown at 11. The cylinder head caps are illustrated at 12 and the cylinders of the pump extend in back of each of these heads. Of course, this invention is concerned more directly with these caps, the cylinders, and the liners and seal assemblies therefor.

Referring toFig. 2, this particular illustration of the pump is shown to be of the type .having two spaced apart

chambers

13 and 14 with aliner 15 extending there between. The pump body about the chambers at 16 and 17 provide the cylinder. The cylinder head has its opening 18 and has an outer surface 19 againstv which the cap 20 is secured.

pump of the class It will be noted that the liner 15, in the arrangement shown, has a metal-to-metal support with the pump body to hold the liner against movement in either direction whereby the force imposed on the liner due to the reciprocation of the piston is transmitted through the rigid metal supports to the pump body and is not transmitted through any portion of the liner or cap packing. In this embodiment, the metal-to-metal backup for the liner holding it against movement away from the cap is provided by the use of a three-pronged cage 21. One end 22 of the cage is provided with an annular web, the opening of which fits over the polish rod packing stuffing box 23. This provides a central alignment for the cage and, of course, the portion 22 has a metal-to-metal abutment with the pump body portion 24 which surrounds the stufilng box. The prongs on the cage are opened at their ends and abut one end of the liner. The openings between the prongs permit the use of the customary liner retrieving tool for removing the liner.

The liner holddown is also metal-to-metal and includes the cage 25 having the usual openings into the chamber 13, the cap 20, the central holddown stud 26, cap plug 27, and the cap screws 2?. it will be noted that the cap 20 is made up of the ring which is held in metalto-metal abutment with surface 19 on the cylinder head by the cap screws 28. This may be made up tight so as to pre-stress the series of screws 28. The plug 27 has a quick change connection to the ring, preferably a heavy fast lead Acme-type threaded connection, with stop means in the form of a shoulder or flange 27a tolimit this threaded connection. With this arrangement, the plug may be quickly screwed down tight until the shoulder 27a is in tight abutment with the cap ring so as to pre-stress the threaded connection thereby eliminat- 2 ing any back lash or looseness in the threads to prevent pulsation due to the reciprocation of the pump piston. Similarly, the holddown stud 26, which has one end engaging the cage 25, may be made up tight to pre-stress the threaded connection and the lock nut 29 may then be it tightened to maintain this pre-stressed condition.

It is to be noted that in this arrangement, the liner 15 has a uniform external diameter and may be fabricated from tubing stock without the necessity of forming annular flanges thereon either by welding, brazing or turning a shoulder from the tube stock. This materially reduces the cost of the liner because it means that a minimum of machining or other fabricating work need be performed on the liner and prevents wastage of material by machine work required to form a shoulder on the outside of the liner.

A seal is provided between the liner and the pump body intermediate the two

chambers

13 and 14 and in this type of pump actually the seal employs two seal assemblies, but both are intermediate the chambers. One of the seal assemblies seals between the portion 16 of the pump cylinder and the liner, and the other between portion 17 of the pump cylinder and the liner. In each instance, the liner packing includes an expansible material or seal ring 30 and an expander ring of suitable material 31, preferably crowned. The surface 17 is provided with an outturned shoulder against which one metal ring 31 is based and a suitable spacer 32 abuts the associated expanding seal ring 30. The force for expanding the inner sealing assembly is transmitted through the spacer 32 and also through the

rings

36 and 31 which are disposed between surface 16 of the pump cylinder and the exterior of the liner. Another spacer ring 33 is positioned in chamber 13 and holds the

outer packing

30 and 31 in place and transmits the expanding force for both of the liner packings. This spacer 33 is suitably perforated to provide for communication between chamber 13 and the interior of the liner. It will be noted that in the interest of simplicity the valves for the

chambers

13 and 14 have not been shown.

A cap packing is provided for sealing the opening of the cylinder head and in the embodiment shown, seals between the imperforate face of cage 25 and the cylinder head opening 13. Thus, the cap per se provides no sealing function and could be a spider. For the purpose of this specification and the appended claims, therefore, the term cap is used to embrace a spider or similar structural member as well as a continuous member such as shown in the various figures. The cap packing includes an expanding ring or seal ring 34 and an expander ring 35 similar to

rings

30 and 31, respectively. This seal assembly is held against spacer 33 by gland 36 which may be tightened by the parts or studs 37 extending through the cap plug 27. With this arrangement, it is seen that a sealing means has been provided between the liner and the pump body intermediate the chambers and for the cylinder head opening, which are of the are ternally energized type so that in service if leakage should occur the packings may be tightened by means of the studs 37. With the type of pump shown, having the opening between the body portions 16 and 17, if leakage occurs past the liner packing, it may be readily seen. A telltale opening may also be provided in the ring 20 or plug 27, as will be more fully explained in connection with the Fig. 5 and Fig. 6 embodiments, to indicate any leakage past the cap packing.

The seal assemblies for the liner and also for the cylinder head opening are all arranged so that the force imparted to the liner by reciprocation of the piston, which has not been shown in the interest of simplicity, is not transmitted through either of the seal assemblies. The sole force imposed on the seal assemblies is that utilized to externally energize the packings, and this need he only great enough to insure a pressure within the packings which is greater than the fluid pressure developed by the pump. The packings are not subjected to the pounding due to the drag of the piston onlthe liner during its reciprocation and the expansible portion of each seal assembly may be enclosed in a substantially enclosed space provided by relatively close fitting parts so that there is little danger of extruding the material of the seal rings. The metal-to-metal holddown for the liner provides a rigid support for the liner to withstand the drag of the piston and the arrangement can all be pre-stressed to provide a sort of hoop stress to prevent even slight movement of the liner in operation of the pump.

The plug 27 and the opening of cap ring 20 preferably are of such dimension that the liner, the

cages

21 and 25 and the entire internal portions of the liner seal and cap seal arrangements may be withdrawn from a pump and inserted therein through the cap opening when the plug 27 is removed. This makes for a quick change and materially reduces the time which would otherwise be required for removing the series of cap screws 28. The ring 20 is left in tight abutment with surface 19 and the plug 27, upon reassembly of the liner and seals, may be made up tight in the ring 21 with the shoulder 27a abutting the ring so as to properly pre-stress the threaded connection. The stud 26 can then be tightened and lock nut 29 tightened to complete the liner holddown. The liner tightening studs 37 can be suitably adjusted to externally energize the liner and cap seals.

In this embodiment of the invention, the cage 21 is really an adapter to permit utilization of the inventive concept in existing pumps. In new pumps, a shoulder would be provided as an integral part in the pump body for resisting movement of the liner 15 in the direction away from the cylinder head.

In the Fig. 3 embodiment, it is seen that the righthand end of liner 15 is seated against shoulder 17a formed on the pump body itself. This eliminates the necessity for a cage such as 21 in Fig. 2. The arrangement is the same as in Fig. 2 except for this change.

. The embodiment of Fig. 5 shows one manner in which this invention may be utilized in a diflerent type of pump. The basic differences in this typeof pump from that of Fig. 2 is that the body is substantially continuous between'the spaced apart pump chambers 13a and 14a.

The liner 40 isheld in place by metal-to-metal abutment between the pump and' liner by utilization of a cage 41 of somewhat diflferent shape than cage 21 and the'abutting ends of the liner and cage are tapered to pr'ovidefor centering of the liner. The cage 41 also has an'ope'ning for receivingthe polish rodstuifing box 23a to centralize or align the cage 41. The holddown cage 42 functions similarly to cage 25 and is held in place by the plug 43 and central holddown stud 44 and lock nut 45. The plug has a quick change connection with the cap ring 46 in the form of fast lead, heavy, Acmetype threads. The cap screws 47 secure the ring 46 against the cylinder head of the pump.

The liner packing assembly includes two expander and expanding rings'48 and 49, respectively, and an intermediate short spacer or lantern ring 50. This assembly is held between an out-turned shoulder 5'1 on the inner cylinder bore of the pump body and a spacer ring 52. The outer end of the spacer ring 52 provides a shoulder for the cap packing which includes the expander ring 53 'andexpanding ring 54. A shoulder or flange 43a formed on the plug 43 abuts the expanding ring 54 and provides the adjustment for externally energizing both the liner and cap seals. The cap seal assembly, of course, includes the imperforate face of cage 42 and the cap seal takes place between this imperforate face and the inner wall of the cylinder bore at the cylinder head.

The plug 43 may be provided with suitable handles 43b for facilitating tightening of the plugand the plug is tightened against the packing prior to adjustment of the holddown stud 44 for the liner. This type of plug forthe cap is not as desirable as the one shown in Fig. 2 in that there is a tendency for the flange 43a to drag on the expanding ring 54 when tightening the packing which may be minimized by' use of an intermediate Washer (not shown), and also the packing must be tight ened suificiently to pre-stress the threaded connection between the ring 46 and plug 43. Normally the packing need not be tightened to this extent to provide the seals, and for these reasons, the cap shown in Fig. 2 is preferred although quite satisfactory results may be obtained by, the cap arrangement of Fig. 5 and of Fig. 6 in many uses. This arrangement has the advantage of economy in that the plurality of liner studs is not required.

In Fig. 5 it will be noted that a telltale opening has been provided at 55 so that if leakage occurs about either section of the liner seal on either side of the lantern ring 50, this leakage will beindicated through the telltale opening 55 and the packing can be tightened. Of course, this tightening cannot be accomplished without backing oif holddown stud 44 which can then be re-tightened after the packing has been tightened. The cap 46 may be provided with a telltale opening 56 to indicate any possible leakage past the cap seal assembly. This opening 56 could, of course, be located in the plug. Where leakage pasteither the liner or cap seal assembly is quickly noted, the leakage may be stopped by tightening up on the packing. If the leakage exists for any length of time, usually it will require replacement of the parts in order to stop the leakage because of the cutting'actiou of the abrasive fluid handled by the pumps under the extreme pressures encountered in such pumps. Here again the pump liner has been fabricated with a uniform external diameter so as to eliminate the necessity of forming a shoulder on the exterior diameter.

. 6 have flat shoulders for abutting thefi'at endof a liner 40b. The prongs may be made quite heavy and the space between the prongs make it possible to utilize the usual liner extracting tool for removing the'liner.

In Fig. 6, the arrangement of' the plug 43 and cap 46 is the same as in Fig. 5. However, a different embodiment is shown wherein the liner can be formed with an external shoulder instead of having a uniform external diameter and still utilize the present. invention.

In the Fig; 6 embodiment, the liner 60 has a flange 61 thereon which may either be welded or brazedin place or may be formed by machine Work. However, this flange is located so as to engage directly upon the shoulder 62 formed on the pump body and no packing should be used between the flange and the shoulder 62. With this arrangement, the adapter cage such as 41 and 21 in Figs. 5 and 2, respectively, need not be employed because the flange and shoulder 62 provide the metal-to-metal abut ment between the liner and pump body. The holddown arrangement, in the'Fig. 6 embodiment; for the lineris substantially the same as in Fig. 5. The liner packing is essentially the same as the Fig. 5 embodiment except that the seal assembly including the lantern ring 50 and the two sets of expander and expanding

rings

48 and 49 are arranged to abut the outer shoulder of flange 61 instead of abutting the. shoulder 62' of the pump body; A suitable telltale opening 64 may be provided in the pump body to indicate leakage past this seal assembly. The cap packing'arrangement is just the same as that shown in Fig. 5.

The Fig. 7 embodiment is similar to that of Fig. 5 except that a modified cap is shown. Here the cap 65 is constructed in one piece without the removable plug. The cap carries a central holddown stud 66 for the liner with a lock nut 67 and a plurality of liner tightening studs 68 which actuate a follower gland 69 for tightening up on both the liner packing of the cap packing. The holddown cage and the seal assemblies for the cap and liner have been given the same numbers as in Fig. 5 except for the'follower gland 69jand the tightening stud 68 which constitute theonly differences of the parts in this embodiment.

The Fig. 8 embodiment is the same as the Fig. 5 embodiment except that the plug 43a of the cap has a lug 43b engageable with cage 42 for the liner holddown eliminatingthe necessity of the use of a central adjustable holddown stud 44 and lock washer 45.

One other diiference is that a plurality of seal tightening means is provided in the plug in the form of studs 70 which engage the'follower ring 71 to tighten both the cap and liner packing. The type of pump shown in Fig. 8 is similar to that shown in Fig. '2 and employs the liner seal assembly shown in connection with Fig. 2.

By comparing the caps of Fig. 5 and Fig. 8, it is seen that in each instance the plug itself provides an adjustable means for engaging one of the liner holddown cages and the gland for expanding the cap packing. In Fig. 5, the adjustment of the plug provides for tightening of the seals and in Fig. 8 the adjustment of the plug provides for holding the liner in place. In each instance, the other function'is performed by adjustable parts carried by the plug. In Fig. 5, the adjustable part is the stud 44 and lock nut 45 while in Fig. 8 the adjustable parts are the studs 70.

In the drawings andv specification, there has been described numerous features and subcombinations illustrating the several manners in which this invention may be practiced in difierent types of pumps; It is to be understood that these features and subcombinations'.-may be utilized in various combinations and in the various types of pumps on the market and this is contemplated by the claims.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the structure.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

' The invention having been described, What is claimed is: 1. In a heavy duty high pressure pump of the type having a body with two spaced apart pump chambers, one of the chambers having an opening with a removable cap therefor, a liner extending between the chambers and communicating therebetween, a rigid means between the liner and body to support the liner against movement away from the body cap, rigid means holding the liner against movement out of the opening, said last-mentioned means including means independent of the liner rigidly securing the cap to the body and adjustable rigid means interposed between the cap and the liner, externally energized packing means for sealing between the exterior wall of the liner and the pump body and located between the chambers, externally energized packing means for sealing the opening and means carried by the cap independent of the cap securing means and externally actuatable for applying mechanical pressure to the two packing means for energizing same.

2. In a heavy duty, high pressure pump of the type having a body with two spaced apart pump chambers, one of the chambers having an opening with a removable cap therefor, a liner extending between and communicating with the chambers, means for securing the cap in metal-tometal contact with the pump body, the cap having an opening therethrough, metal-to-metal means supporting the liner in the pump body against movement along its longitudinal axis away from the cap, means including a plug having a quick change metal-to-metal mounting in the cap opening providing a rigid adjustable metal-tometal holddown for the liner to prevent its movement toward the cap and means sealing between the liner and body intermediate the chambers and sealing off the opening, the opening through the cap having a dimension large enough to permit passage of the liner and the sealing means therethrough.

3. The combination of claim 2 wherein the liner has a substantially uniform exterior diameter.

4. The arrangement of claim 2 wherein the cap has a telltale opening formed therein to indicate leakage past the seal for the opening.

5. In a heavy duty, high pressure pump of the type having a body with two spaced apart pump chambers, one of the chambers having an opening with a removable cap therefor, a liner extending between and communicating with the chambers, means for securing the cap in metalto-metal contact with the pump body, the cap having an opening therethrough, metal-to-metal means supporting the liner in the pump body against movement along its longitudinal axis away from the cap, means including a plug having a quick change metal-to-metal mounting in the cap opening providing a rigid adjustable metal-tometal holddown for the liner to prevent its movement toward the cap, packing means for sealing between the exterior wall of the liner and pump body and located between the chambers, packing means for sealing the opening and means externally actuatable and having parts carried by and extending through the plug for applying mechanical pressure to the two packing means for energizing same, the opening through the cap having a dimension large enough to permit passage of the liner and the sealing means therethrough.

6. In a heavy duty, high pressure pump of the type having a body with two spaced apart pump chambers,

one of the chambers having an opening with a removable cap therefor, a liner extending between and communicating with the chambers, means for securing the cap in metal-to-metal contact with the pump body, the cap having an opening therethrough, metal-to-metal means supporting the liner in the pump body against movement along its longitudinal axis away from the cap, means including a plug having a quick change metal-to-metal mounting in the cap opening providing a rigid adjustable metal-to-metal holddown for the liner to prevent its movement toward the cap, packing means for sealing between the exterior wall of the liner and pump body and located between the chambers, packing means for sealing the opening and means engageable by the plug for applying mechanical pressure to the two packing means for energizing same.

7. in a heavy duty, high pressure pump of the type having a body with two spaced apart pump chambers, one of the chambers having an opening with a removable cap therefor, a liner extending between the chambers and communicating therebetween, means providing a metal-tometal abutment between the pump and one end of the liner, a holddown cage having a metal-to-metal connection with the other end of the liner, said cage having an imperforate face adjacent to and confronting the opening,

packing means between the liner and body intermediate the chambers, packing means including a follower gland between the cage face and body for sealing off the opening, the cap having an opening of a dimension to pass the liner, the two packing means and follower gland, a plug for the opening having a heavy threaded connection with the cap, means on the plug engaging one of the cage face and the follower gland and adjustable means carried by the cap for engaging the other of said cage face and follower gland thereby providing independently adjustable tightening means for the liner holddown and for expanding the packing.

8. As a subcombination, a cap for use in conjunction with a cylinder head of a heavy duty, high pressure reciprocating piston-type pump comprising, a ring with a series of circumferentially arranged openings, the opening through the ring being of such a dimension as to readily pass a liner and packing adaptable for use with the pump for which the cap is intended, one endwise face of the cap being flat for abutting an end face of a pump cylinder head, a plug having a heavy threaded connection to the ring, a series of packing tightening studs extending threadedly through the plug and a central liner hold down stud extending threadedly through the plug with a lock nut on the stud for pre-stressing it.

9. The cap of claim 8 wherein the ring is formed with a telltale opening therein located to communicate be- 7 tween a point interiorly of the ring diameter adapted to abut a cylinder head and the exterior of the ring with the cap in place on a pump.

10. As a subcombination, a cap for use in conjunction with a cylinder head of a heavy duty, high pressure reciprocating piston-type pump comprising, a ring with a series of circumferentially arranged openings, the opening through the ring being of such a dimension as to readily pass a liner and packing adaptable for use with the pump for which the cap is intended, one endwise face of the cap being flat for abutting an end face of a pump cylinder head, a plug having a heavy threaded connection to the ring, stop means on the plug adapted to abut the ring to limit threading of the plug in the ring for pre-stressing' the threaded connection therebetween, a series of packing tightening studs extending threadedly through the plug and a central liner holddown stud extending threadedly through the plug with a lock nut on the stud for pre-stressing it.

11. In a heavy duty, high pressure pump of the type having a body with two spaced apart pumping chambers, one of the chambers having a cylinder head opening, a liner extending between the chambers and communicating therebetween, means between the liner and pump body providing a releasable metal-to-metal holddown for the liner holding it rigidly against movement in either direction along its longitudinal axis and including a part closing said opening and a part rigidly carried on said body and adjustably bearing against the exterior of said part closing said opening, externally energized seal means between said body and said liner intermediate said chambers and other externally energized seal means between said part closing said opening and said body about said opening, said seal means being in series so that sealing pressure applied to one will be applied to all, and means exteriorly of said last mentioned seal means and of the 10 part closing said opening adjustably bearing against said last mentioned seal means to apply sealing pressure to said seal means.

References Cited in the file of this patent UNITED STATES PATENTS 1,510,042 Clewett Sept. 30, 1924 2,198,301 Campbell Apr. 23, 1940 2,259,432 Failing et a1 Oct. 14, 1941 2,345,370 Whann et al Mar. 28, 1944 2,584,518 Walton Feb. 5, 1952 2,701,743 Mattingly et a1. Feb. 8, 1955