US2526561A

US2526561A - Variable stroke drive for oscillatory members, more particularly for pumping apparatus

Info

Publication number: US2526561A
Application number: US648378A
Authority: US
Inventors: Amos L Keltner
Original assignee: Individual
Current assignee: Individual
Priority date: 1946-02-18
Filing date: 1946-02-18
Publication date: 1950-10-17
Anticipated expiration: 1967-10-17

Description

Oct. 17, 1950 A. L. KELTNER 2,526,561

VARIABLE STROKE DRIVE FOR OSCILLATORY MEMBERS, MORE PARTICULARLY FOR PUMPING APPARATUS Filed Feb. 18, 1946 4 Sheets-Sheet 1 AWS x qmos LAELTNE Oct. 17, 1950 A. L KELTNER 2,526,561 VARIABLE STROKE DRIVE FOR OSCILLATORY MEMBERS,

MORE PARTICULARLY FOR PUMPING APPARATUS Filed Feb. 18, 1946- 4 Sheets-Sheet 2 FlL-ZZ Z I A;

A OS L/(ELT/YEK Za/MYWZfl Oct. 17, 1950 A. L. KELTNER 2,526,561

VARIABLE STROKE DRIVE FOR OSCILLATORY MEMBERS,

MORE PARTICULARLY FOR PUMPING APPARATUS 7 Filed Feb. 18, 1946 4 Sheets-Sheet 3 Oct. 17, 1950 A. L. KELTNER ,52

- VARIABLE STROKE DRIVE FOR OSCILLATORY MEMBERS,

MORE PARTICULARLY FOR PUMPING APPARATUS Filed Feb. 18, .1946 4 Sheets-Sheet 4 AMOS L. KELTNER Patented Oct. 17, 1950 VARIABLE STROKE DRIVE FOR OSCILLA- TORY MEMBERS, MORE PARTICULARLY FOR PUMPING APPARATUS Amos L. Keltner, Wichita, Kans.

Application February 18, 1946, Serial No. 648,378

12 Claims.

This invention relates to variable stroke drives for oscillatory members and more particularly to variable stroke drives for the rocking or oscillatory beams of pumping apparatus.

In Well known pumping apparatus now widely used in the pumping of oil or water, a rod extending vertically into a well is connected at its top to one end of an oscillatory pumping beam mounted to rock on a so-called Samson post. Oscillation. of the beam is effected by mechanism usually including a drive shaft and a connecting rod or pitman connected to the beam by a wrist pin. and connected to the drive shaft by an eccentric device, for example, a cam and follower, or eccentric and strap or a pitman and crank pin rotatable with the drive shaft but being offset or eccentric with respect to the drive shaft axis.

Numerous difficulties have been encountered in the practical use of apparatus of this known kind. Due to the oscillatory forces developed in operation, failure of wrist pins, wrist pin bearings, pitman bearings, cranks, equalizer, and equalizer saddle bearings, has been common. When a pitman breaks, the continued application of power to the drive shaft can cause serious damage to the other parts of the apparatus, particularly to beam assembly.

An object of the present invention is to provide an improved mechanism for transmitting drive to an oscillatory member, e. g., the beam of a pumping apparatus in which the parts which heretofore have caused the difficulties'referred to are eliminated, and in which a novel drive. transmitting mechanism, including one or more flexible elements, is interposed between the drive shaft 1 and. the oscillatory member or beam.

Another object of the invention is to provide a drive transmitting mechanism of the character referred to which is adaptedeasily to be adjusted or set for varying the amplitude of oscillation of the oscillatory member, and in the case of pumping apparatus, consequently varying the pump stroke. In order to vary the amplitude of oscillation of a pump beam or the likejin the previously known z member cyclically and automatically changes gradually and progressively to minimum, then gradually and progressively increases to maximum, then again changes gradually and progressively to minimum, and so on.

Other objects of the invention will become apparent from a reading of the following description, the appended claims, and the accompanying drawings, in which:

Figure 1 is a side elevation of a pumping apparatus' embodying the invention;

Figure 2 is a section on the line 2-2 of Figure 1;

Figure 3 is a detailsection on the line 3-3 of Figure 1; v

Figure 4 is a fragmentary elevational view of a modified construction embodying the invention;

Figures 5 5* 5, 5 and 5 are companionviews showing diagrammatically the relative positions of parts of the driving mechanism corresponding to different positions of a drive shaft when the parts are adjusted for a maximum amplitude of oscillation of an oscillatory member or pump beam; I

Figures 6, 6 6", 6 and 6 are companion views similar to Figures 5 to 5 inclusive, but with the. parts adjusted for a smaller amplitude of oscillation.

Figures 7 7 7, 7 and 7 are companion views similar to Figures 5 to 5 inclusive, but with the parts adjusted for a still smaller amplitude of oscillation. I

Figures 8 8 and 8 are companion views show-'- ing diagrammatically the automatic cyclic variation of the phase relationship of parts of the driving mechanism by which the amplitude of oscillation of the oscillatory member cyclically changes from maximum gradually and progressively to minimum, then increases gradually and progressively to maximum, then again decreases gradually to minimum, and so on; and

Figure 9 is a perspective view of a locking pin.

The representative embodiment of the invention shown in Figures 1, 2 and 3 includes a base I which maybe formed in any conventional manner from standard rolled sections welded or otherwise joined together. The base I is adapted to support the whole apparatus so'that it may be moved'into cooperative position with respect to a well casing or tube 2. An oscillatory pumping beam 3 is mounted to rock on a pintle 4 carried at the top of a Samson post structure 5 secured to the base I. The beam 3 is provided witha removable head 6 equipped or formed with a hook 1 engaged by a cable 8 connected at its lower end to a polish rod 9 extending into the well casing 2. The oscillation of the beam 3 causes the polish rod 9 to be raised and lowered alternately in the casing 2. The Samson post structure 5 is provided with limiting stops l and H adapted to be engaged by the beam 3 on opposite sides of the pintle 4 so as to prevent overswingin of the beam 3 in the event of breakage of the pumping parts or the mechanism for rocking the beam 3.

A power unit [2 which may be an electric motor, internal combustion engine, or any other suitable prime mover, is mounted on the base I in a manner to be described later. Sheaves IS on the power unit l2 are connected by V-belts 14 to larger sheaves l5 mounted on a countershaft l6 journaled in a bearing ll supported by a standard l8 carried on the base Fast on the countershaft 16 are small sheaves [9 connected by V-belts 20 to larger sheaves 2i secured to a drive shaft 22 journaled in bearings 23 on a base-supported standard structure 24.

In accordance with the invention, drive transmitting connections interposed between the rotary driving member or shaft 22 and the oscillatory pumping member 3, comprise two substantially

circular members

25 and 26 respectively mounted on the shaft 22 and a pintle 21 on the beam 3, the

members

25 and 26 being mounted with their centers disposed eccentrically with respect'to the drive shaft 22 and pintle 2?, respectively. The driving connections also include an endless flexible member 28 trained around and operatively connecting the substantially

circular members

25 and 26.

In the form shown in Figures 1 and 2, the substantially

circular members

25 and 26 are toothed sprockets and the endless member 28 is a flexible chain trained around the sprockets to engage the teeth thereof. The sprockets are of the same pitch diameter and contain equal numbers of teeth.

The arrangement is such that when the drive shaft 22 is driven in a clockwise direction, the

distance between shaft 22 and the pintle 21 until I.

the down stroke of the rod 9 has been completed, after which the changing of the relative positions of the

sprockets

25 and 26 will be such as to move the pintle 21 back toward the drive shaft 22, thereby rocking the beam 3 counter-clockwise and lifting the rod 9.

The operation of the parts as described generally above may be understood better by considering several successive specific phases of the operation, as shown diagrammatically in Figures 5 to 5 inclusive. Figure 5" shows the drive shaft 22, the pintle 21, and the

sprockets

25 and 26 in the same relative positions these parts are shown in Figure 1, that is, with the beam 3 in its up position, in which the polish rod 9 is raised. The center of the sprocket 25 is below the drive shaft 22, and the center of the sprocket 26 is directly above the pintle 21. Thus, the eccentricities of the

sprockets

25 and 26 are in mutually different phase relationship with a line intersecting their respective axes of rotation. When the drive shaft 22 is rotated through 45 degrees, the parts will be in the positions shown in Figure 5. The portions of the sprocket peripheries 'most distant from each other have tended to move toward each other with a consequent tendency to slacken the chain 28. Inasmuch as the polish rod 9 biases the beam 3 clockwise, tending to lift the pintle 21, the tendency to slacken the chain 28 results in no actual slackening, but instead brings about a raising of the pintle 21 and lowering of the polish rod 9. When the driving shaft 22 has moved through degrees to the position shown in Figure 5, there is a further tendency for the chain 28 to slacken, resulting instead in further lowering of the polish rod 9. Figures 5 and 5 show additional successive positions occupied by the parts after the shaft 22 has rotated through degrees and degrees,

.; respectively. It will be seen that when the parts are positioned as shown in Figure 5 the shaft 22 and the pintle 2'! are separated to the maximum extent. This position of the parts corresponds to the lowermost position of the polish rod 9. The amplitude of oscillation of the beam 3, and consequently the length of the stroke of the rod 9 may be measured by the difference between the distance V between the

parts

22 and 27 as shown in Figure 5 and the distance V between the same parts as shown in Figure 5 During the next half revolution of the drive shaft 22, in which it turns clockwise from the Figure 5 position to the Figure 5 position, the pintle 2! will be caused to approach the drive shaft 22 gradually, thereby rocking the beam 3 counter-clockwise and raising the polish rod 9.

Figures 6 to 6 inclusive show diagrammatically different phases of a. one-half operating cycle when the parts are adjusted for a shorter stroke. It will be seen that in Figure 6 the starting position of the lower sprocket 25 is the same as in Figure 5 that is, its center is directly below the drive shaft 22. However, in its starting position the upper sprocket 26 is displaced 45 from the starting position shown in Figure 5 By observing the progressive changes in the distances between the

parts

22 and 27, as shown throughout Figures 6 to 6 inclusive, it will be seen that the movement of the beam 3 is accomplished generally in the same manner for the adjustment shown in Figures 6 to 6 as for the adjustment shown in Figures 5 to 5 When the parts have been adjusted to start in the relative positions shown in Figure 6 the amplitude of oscillation of the beam 3 and consequently the length of stroke of the rod 9 may be measured by the difference between the distance VI shown in Figure 6 and the distance VI shown in Figure 6 It will be noted that the difference between the distances VI and VI is less than the difference between the distances 5 and 5 Consequently, the adjustment of the parts shown in Figures 6 to 6 produces a shorter stroke.

Figures '7 to 7 inclusive, show the parts adjusted for a still shorter stroke. Here again, the center of the sprocket 25 starts in a position directly below the axis of the shaft 22, and the sprocket 26 is displaced 90 degrees from the position shown in Figure 5 It will be understood that many intermediate stroke adjustments may be made by setting the sprocket 26 to start in other selected displaced positions.

Means are provided for facilitating the adjustment of the relative positions of the

sprockets

25 and 26 to obtain the variation of stroke described above. A clamp 29 is adapted to be secured temporarily to the polish rod 9 so as to rest upon the top of the casing 2 for supporting the rod 9 and relieving the beam 3 of the weight of the rod. The sprocket 26 is formed with a hole- .30' adapted to. register with a. selected one. of: a plurality of apertures 3i in the beam: 3;. the apertures being deployed circumferentiallyabout: the axis of the'pintle 21. A locking pin bar 32- such as isshown in Figure.- 9,. may be inserted through the hole 30 and a selected aperture 3| for: releasably locking the sprocket. 26: against rotation. tions of the sprockets and 26' the apparatus i'szstopped' and the clamp: 29. is secured to. the. rod. 9- and in engagement with the top of the casing 2 Then the countershaft' sheave i5. is turned by hand to rotate the sprocket. 25 and. the sprocket 26.. until the. hole 302' in the latter registers with theaperture 3| in the beam. corresponding to; the. adjustment. desired. The pin 32 is then inserted through the hole and. registering aperture. 3|. Turning of the sprocket 25. will not-v be accompanied by raising. of the pintle 21 because the. clamp 29 prevents the rod. 9 from rocking the beam 3,.v Consequently, the chain 28 will be slackened sufliciently to permit its. being opened or" unlinked: and disengaged from the sprocket 25. When the chain has been disengaged, the countershaft sheave I5 is turned. reversely until the center of the sprocket 25 is disposed directly below the axis. of the drive shaft. 22.. The chain 28 may then be reengaged with the sprocket. 25 and closed: or re-linked,. and the locking pin. 3.2 will thenbe withdrawn to. prepare the apparatus for further'operation. with a: different stroke.

Inthe modification shown in Figure 4, thegeneral arrangement of the parts is the. same as that' shown inFigures i and. 2, but the driving connectionsv include sheaves: 33 and 34 and belts 35 inplace of the sprocket and chain drive shown in Figures 1 and 2. The construction shown in Figure 4 has the advantage of enabling adjust.- ment of. the. relative positions. of thev sheaves 33 and 3.4. to bemade more: easily than the; adjustment' of the relative positioning of the sprockets 2:5 and: 26.. This greater ease in adjusting is due to the ability ofv thelowersheave 33 tobe. turned reversely' to its starting position, while the. upper sheave. 34 is locked against rotation, without its being necessary to remove the belts 35. The. slackness' of the belts 35 alone is suflicient to. permit thesheave 33 to be returned to its starting position- Intherpnmping of many oil. wells it is preferred. if not the necessary practice, to pump only at intervals which should be rather regular. For example, a well may be pumped for, say, eight minutes then not pumped for about ten minutes, then pumped againfor about: eight min utes, and so on. Such interval pumping usually has been accomplished by the use of electrical time clock controls, which, however, cannot always be used; particularly in non-electrified In order to adjust the relative posipump stroke automatically diminishes progresonly'a desired agitation in the well, after which 6; the. stroke increases to an effective. pumping am.- plitudeuntil it reaches a maximum. The cycle is. then repeated.

This automatic cycling of the pump stroke from maximum to zero and then back to a maximum is accomplished by the simple expedient of employing substantially circular members .corresponding to. the

sprockets

25 and 26, shown in Figure l, but which are of difierent pitch diameters, or stated differently, have difierent numbers of teeth. Such an arrangement is shown diagrammatically in Figures 8 8 and 8. Figure 8 shows parts in their datum or starting positions. A sprocket 36 fast on the drive shaft 22 has fifty teeth and is positioned with. its own center 36 directly below the drive shaft 22. One tooth a is intersected by a line drawn through the axes of the shaft 22. and pintle 21. A sprocket 38 having forty-eight teeth is journaled on the pintle 21 with its own center 38 disposed directly above the pintle. One tooth a of the sprocket 38 is intersected by the line joining the centers of the

parts

22, and 21. Another tooth, four removed from the tooth a, is designated b. A chain 31 is trained around the sprockets 36 and 39.

Figure 8 shows the parts approximately in the relative positions they will occupy after two complete clockwise rotations of the sprocket 36. This sprocket of course will be in the same position as shown in Figure 8 However, due to the difference in the numbers ofv teeth in the two sprockets 36' and 38, and the corresponding difference in their pitch diameters, the sprocket 38 will have turned angularly more than the sprocket 36 so that when the sprocket 36 has turned twice through 360 degrees the sprocket 38 will have turned twice through 360 degrees plus an angle measured substantially by the angle included between the teeth a and b. Therefore, the next revolution cycle will begin with the

sprockets

36 and 33 adjusted dififerently from the adjustment shown in Figure 8 and the stroke will be accordingly shorter. During each revolution of the sprocket 36, the sprocket 38 will turn angularly more than 360 degrees, so

that finally the parts will become positioned relatively, as shown in Figure 8, in which the tooth 0: of the sprocket 38 is displaced degrees from the position shown in Figure 8 and the center 38 0f the sprocket 3B is disposed directly below instead of above the pintle 21. At this moment, the parts will be so relatively positioned as to produce no stroke at all. The no-stroke relative'positioning exists only momentarily and as soon as it has been reached, further operation will be accompanied by gradual increasing of the stroke-until finally the parts reach the maximum stroke positions shown in Figure 8*, thus completing a cycle. The cyclic stroke variation takes place during constant speed operation of the prime mover l2 and drive shaft 22, no time clocks or other special timing equipment being needed.

Preferably, means are provided for adjusting the tension of the belts M and 28'. To this end the power unit I2 is fast to a plate 39 which is slidably mounted on: the base I; the standards 18 are supported on a separate plate Ml which be shifted on the plate 39 toward and from the power unit [2. Nuts and bolts indicated at 4| may be'provided for'holdingthe plate 49 in adjusted position on the plate 39 to maintain the belt I 4 at the desired tension. The tension of the belt 20 may be adjusted by sliding the plate 39 and thus moving the power unit l2 and the standard 18- toward or from the power shaft 22..

- clearance for withdrawing the rod 9.

The mechanism shown for sliding the plate 39 includes a nut 42 secured to a plate 43 depending from the plate 39, and a captive screw 44 engaging the nut 22. The screws 51; may be turned for effecting the adjustments by means of a bevel gear couple 45 and a squared shaft 46 arranged to turn the driving gear of the couple 45.

As previously stated, the pumping beam head 5 preferably is removably mounted on the beam 3 so that it may be taken oiT to provide additional Any suitable means, such as bolts til, may be provided for securing the head 6 in operative position.

The pumping beam 3 is shown as being equipped with the usual counterweight 48, the counterbalancing effect of which may be adjusted by means of a screw 49 having threaded connection with a nut or sleeve, not shown, on the counterweight 48, the inner end of the screw 69 being mounted for rotation in, but held against, axial movement with respect to a part 5E1 on the beam.

The constructions disclosed herein embody the invention in the forms now preferred, but it will be understood that some changes may be made without departing from the invention as defined in the claims.

I claim:

1. In a pumping apparatus, a rotary driving member; an oscillatable pumping member; driving connections between said members comprising a first substantially circular member driven'by said driving member and mounted to turn about the axis of said driving member with the axis of said substantially circular member eccentric to the axis of said driving member, a second substantially circular member journaled on said oscillatable member to rotate about an axis eccentric to the axis of said second substantially circijlar member, and an endless flexible member trained around and connecting said substantially circular members, the respective eccentricities of said substantially circular members being in mutually diiierent phase relationship with a line intersecting the axes of rotation of said substantially circular members; and means for holding said oscillatable pumping member stationary, whereby upon movement of the center of one of said substantially circular members towards the center of the other of said substantially circular members while said oscillatable pumping member is held stationary, said endless flexible member will be slaekened so as to permit one of said substantially circular members to be rotated about its axis to change the relative phase relationship of the eccentricities of said substantially circular members.

2. In a pumping apparatus, a rotary driving member; an oscillatable pumping member; driving connections between said members comprising a first substantially circular member driven by said driving member and mounted to turn about the axis of said driving member with the axis of said substantially circular member eccentric to the axis of said driving member, a second substantially circular member journaled on said oscillatable member to rotate about an axis eccentric to the axis of said secondsubstantially circular member, and an endless flexible member trained around and connecting said substantially circular members, the respective eccentricities of said substantially circular members being in mutually different phase relationship with a line intersecting the axes of rotation of said substantially circular members; and means for releasably locking one of said substan- 8 l tially circular members against rotation whereby, upon operative disconnection of said endless flexible member from either of said substantially circular members and rotation of the substantially circular member other than the locked member, said phase relationship will be changed with consequent change in the stroke of said oscillatable member.

3. In a pumping apparatus, a rotary driving member; an oscillatable pumping member; and driving connections between said members comprising a first substantially circular member driven by said driving member and mounted to turn about the axis of said driving member with the axis of said substantially circular member eccentric to the axis of said driving member, a second substantially circular member journaled on said oscillatable member to rotate about an axis eccentric to the axis of said second substantially circular member, the pitch diameter of said second substantially circular member being different from the pitch diameter of said first substantially vertical member, and an endless flexible member trained around and connecting said substantially circular members, said connections having the inherent characteristic, due to said difference in pitch diameters, of cyclically gradually and progressively increasing the pumping member stroke, then gradually and progressively decreasing the pumping member stroke, then again gradually and progressively increasing said'pumping member'stroke, and so on during constant speed rotation of said rotary driving member.

4. In a pumping apparatus, a rotary drive shaft; a rockable pumping beam; driving connections between said shaft and said beam comprising a first substantially circular member fixed to said shaft eccentrically with respect to the axis of said first substantially circular member, a second substantially circular member journaled on said beam to rotate about an axis eccentric to the axis of said second rotatable member, and an endless flexible member trained around and operatively connecting said substantially circular members, the respective eccentricities of said substantially circular members being in mutually diilerent phase relationship with a line intersecting the axes of rotation of said substantially circular members; a hole in said second substantially circular member eccentric to the journal axis thereof; a plurality of apertures in said beam deployed circumferentially with respect to said journal axis and with any selected one of which said hole is adapted to register; and a locking pin' adapted to be inserted through said hole and a registering. aperture to thereby lock said first substantially circular member against rotation whereby, upon operative disconnection of said endless flexible member' from either of said substantiaily circular members and rotation of said first substantially circular member, said phase relationship will be changed with consequent change in the stroke of said beam.

5. Inv a pumping apparatus, a rotary drive shaft; a rockable pumping beam; and connections including coacting driving and driven rotary members each eccentrically mounted and'of mutually different pitch diameters interposed between said beam and said shaft for transmitting drive-from said shaft to said beam for rocking the beam, said connections inherently cyclically gradually and progressively increasing the beam stroke, then gradually and progressively decreasing the beam stroke, then again gradually and progressively increasing thebeam stroke, and s0 on during constant speed rotation of said shaft.

6. In a pumping apparatus, a rotary drive shaft; a rockable pumping beam; and connections interposed between said beam and said shaft for transmitting drive from said shaft to said beam for rocking the beam, said connections including a pair of eccentrically mounted circular elements of mutually different diameters and a cooperating endless flexible member trained around and drivingly connecting said circular oscillatable member, said mechanism comprising a drive shaft; and connections between said shaft and said member including a pair of sprockets each eccentrically mounted with mutually different numbers of teeth, and a cooperating endless chain trained around and drivingly connect- '7. In a pumping apparatus, a rotary drive shaft; I

a rockable pumping beam; and connections interposed between said beam and. said shaft for transmitting drive from said shaft to said beam for rocking the beam, said connections including a pair of sprockets each eccentrically mounted with mutually different numbers of teeth and a cooperating endless chain trained around and drivingly connecting said sprockets for cyclically gradually and progressively increasing the beam stroke, then gradually and progressively decreasing the beam stroke, then again gradually and progressively increasing the beam stroke, and so on during constant speed rotation of said shaft.

8. Mechanism for transmitting drive to an oscillatable member, said mechanism comprising a drive shaft; and connections including coacting driving and driven rotary members each eccentrically mounted and of mutually different pitch diameters between said shaft and said member, inherently cyclically gradually and progressively increasing the stroke of said member, then gradually and progressively decreasing the stroke of said member, then again gradually and progressively increasing said stroke, and so on during constant speed rotation of said shaft.

9. Mechanism for transmitting drive to an oscillatable member, said mechanism comprising a drive shaft; and connections between said shaft and said member including a pair of eccentrically mounted circular elements of mutually different diameters, and a cooperating endless flexible member trained around and drivingly connecting said circular elements for cyclically gradually and progressively increasing the stroke of said member, then gradually and progressively decreasing the stroke of said member, then again gradually and progressively increasing said stroke, and so on during constant speed rotation of said shaft.

'10. Mechanism for transmitting drive to an ing said sprockets for cyclically gradually and progressively increasing the stroke of said member, then gradually and progressively decreasing the stroke of said member, then again gradually and progressively increasing said stroke, and so on during constant speed rotation of said shaft.

11. In a pumping apparatus, a rotary drive shaft; a rockable pumping beam; and connections interposed between said beam and said shaft for transmitting drive from said shaft to said beam for rocking the beam, said connections including a pair of eccentrically mounted, drivingly connected, circular elements of mutually different diameters for cyclically gradually and progressively increasing the beam stroke, then gradually and progressively decreasing the beam stroke, then again gradually and progressively increasing the beam stroke, and so on during constant speed rotation of said shaft.

12. In a pumping apparatus, a rotary drive shaft; a rockable pumping beam; and connections interposed between said beam and said shaft for transmitting drive from said shaft to said beam for rocking the beam, said connections including a pair of eccentrically mounted, drivingly connected toothed circular elements the pitch diameters of which are in a ratio of approximately 25 to 24 for cyclically gradually and progressively increasing the beam stroke, then gradually and progressively decreasing the beam stroke, then again gradually and progressively increasing the beam stroke, and so on during constant speed rotation of said shaft.

AMOS L. KELTNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 944,999 Blake Dec. 28, 1909 1,223,283 Kurtz Apr. 17, 1917 1,568,430 Uhl Jan. 5, 1926 1,592,391 Stevenson July 13, 1926 1,782,697 Reschke Nov. 25, 1930 FOREIGN PATENTS Number Country Date 2,092 Great Britain May 22, 1880 A. D. 1880