US3055626A - Hydraulic supports - Google Patents

Description

Sept. 25, 1962 B. TEBB ET L 3,055,626

HYDRAULIC SUPPQRTS .Filed March 29, 1961 4 Sheets-Sheet 1 ,0 24 76 I7 INVENTORSI BERNARD TEBB g. CLARENCE HERBERT PERRY Sept. 25, 1962 B. TEBB ETAL 3,055,626 HYDRAULIC SUPPORTS Filed March 29, 1961 4 Sheets-Sheet 3 INVENTORS BERNARD TEBB 31 CLARENCE HERBERT PERRY BY Wang, $4

Se t. 25, 1962 B. TEBB ETAL HYDRAULIC SUPPORTS Filed March 29, 1961 4 Sheets-Sheet 4 INVENTOR: BERNARD TEBB & cunmcs HERBERT PER BY 1- 4 611W, WiWW' United States Patent Ofifice 3,055,626 Patented Sept. 25, 1962 company Filed Mar. 29, 1961, Ser. No. 99,216 Claims priority, application Great Britain Apr. 9, 1960 3 Claims. Cl. 248-354) This invention concerns hydraulic supports of the type comprising a pair of coaxially arranged tubular members engaged one within the other for relative sliding movement, the inner end of the inner tubular member being provided with a detachable hydraulic ram which slides within and co-operates with the outer tubular member to define a hydraulic pressure or w rking chamber for receiving hydraulic medium under pressure, a hydraulic pump carried by the ram within the interior of the inner tubular member, said interior constituting a reservoir for hydraulic medium, means accessible externally of the support and including a piston connecting rod for operating the pump to transfer hydraulic medium from the reservoir to the pressure chamber, and valve means for enabling hydraulic medium to return from the pressure chamber to the reservoir.

The functions which are required of a hydraulic support comprise extension of the support to the required working height, setting of the support to sustain a predetermined maximum load, unloading of the support when the said load is no longer required to be supported, and subsequent collapse of the hydraulic support to its minimum length. The extension of the support to its required working height is accomplished by simple ptunping to transfer hydraulic medium from the reservoir into the pressure chamber, thereby causing the inner member to extend out of the outer member; and the remaining operations of setting, unloading and collapse are achieved by the provision of suitable valves operable responsive to movement of manually actuated control accessible externally of the support.

It is an object of the invention, in such a hydraulic support, to provide means facilitating the removal of the ram, the pump and the pump operating mean from the inner tubular membe A related object of the invention is to provide a hydraulic support, the various operations of which may be carried out by actuation of a single control member.

According to the present invention, in a hydraulic support of the type described, the pump operating means comprises a hollow cylindrical sleeve secured transversely to and extending within the interior of the upper end region of the inner tubular member, a rockable spindle journalled in said sleeve and having a portion engageable externally of said tubular member for enabling rocking motion to be imparted to said spindle, said spindle being formed with an annular groove intermediate its ends and said groove being positioned within the interior of said tubular member, a removable retaining pin passed through a hole in said sleeve to engage in said groove and retain said spindle in said sleeve, and detachable means connecting the spindle and the upper, free end of the piston connecting rod for causing reciprocation of the piston responsive to rocking motion of the spindle.

The said detachable means is preferably a crank having one end pivotally secured to the connecting rod, and its other end bored to fit over an axially directed dowel or equivalent member extending from the inner end of the spindle the said dowel or equivalent member being arranged in a slot formed in the spindle end face for snugly receiving the crank.

The hydraulic ram may conveniently be arranged to carry not only .the pump, but also the valve means, when the combination of ram, pump, valve means, pump piston connecting rod and crank then constitutes a completely control unit for effecting all the operations required of the support, such control unit being capable of withdrawal as a single entity from the support for maintenance and replacement purposes.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal axial section of a hydraulic pit prop embodying the invention;

FIG. 2 is a similar sectional elevation, to an enlarged scale, of the lower part of the pit prop shown in FIG. 1;

FIG. 3 is a detail, in elevation, showing the various operating positions of the crank; and

FIG. 4 is a perspective view of the prop, partly broken away for clarity.

Referring firstly to FIGS. 1 and 2, the prop shown therein comprises a pair of tubular members 10 and 12, of which the upper or inner member 12 is telescopically engaged within the lower or outer member 10. The bottom end of the outer member 10 is closed by a bottom cap or foot 14 having a peripheral O-ring 15, while the top end of the inner member 12 is closed by a short, tubular extension 16 terminating in a top cap 18, the extension 16 being positioned relative to the member 12 by means of a sleeve 20 which embraces the two and which is welded to member 12 at 22. A bolt 24 passes through the sleeve 20 and extension 16 to secure the latter in place.

At its lower end, the inner tubular member 12 is closed by a hydraulic ram generally designated 26 and forming a close, sliding fit within the outer tubular member 10, and the ram 26 carries a peripheral main hydraulic seal 28. The interior of the outer tubular member 10 below the ram 26 is thereby enabled to act as a pressure chamber into which, by pump means hereinafter more fully to be described, may be forced hydraulic medium normally stored in the interior of the tubular member 12 above the ram 26, the said interior thus constituting a reservoir for hydraulic medium. Admission of hydraulic medium into the pressure chamber efiects telescopic expansion of the prop by causing the inner member 12 to extend outwardly of the outer member 10, the amount of this extension being dependent upon the volume of hydraulic medium transferred from the reservoir into the pressure chamber.

To enable the prop subsequently to be collapsed by permitting movement of hydraulic medium in the reverse direction, the hydraulic ram 26 is formed in two parts 30 and 32 which are mutually separable. The outer part 30 of the ram is secured to the lower end of the inner tubular member 12 by means of screws 34, and the inner ram part 32, which fits within the outer part 30, has at its lower end, an enlarged annular flange 36 between which and the opposed lower end of the ram part 30 is provided a hydraulic seal 38.

The pump means by which hydraulic medium is forced into the pressure chamber below the ram 26 comprises a pump cylinder 40 which is secured to the rear face of the inner ram part 32 so as to extend coaxially within the inner sliding member 12 of the prop, and a two-part pump piston assembly having an axially bored, larger diameter piston 42 with a smaller diameter piston 44 received in the axial bore thereof. The lower end of the axial bore in the larger diameter piston 42 has fixed in it, an end plate 46 which carries an upstanding spigot 48, and the smaller diameter piston 44, which is hollow and formed with a valve seat 50 at its lower end, is provided internally. with a spring-loaded valve ball 52 normally urged into sealing relation on the seat 50, but adapted, when the smaller diameter piston is depressed beyond the lower limit of its normal pumping stroke, to be unseated by the spigot 48. The upper end of the pump cylinder 40 is closed by a neck ring 54 which is secured to the cylinder by means of pins 56, and the pins 56 act as a stop for a retainer plate 58, against which abuts one end or a spring 60 having its other end bearing on the upper face of the outer ram part 30 so as normally to urge the two ram parts 30 and 32 together. To the upper end of the small diameter piston 44, which projects out of the large diameter piston 42 to act as a piston rod, there is secured a clevis 62 having one end of a connecting rod 64 pivotally secured therein, and the other end of the rod 64 is pivotally connected to a crank arm 66 carried on a spindle 68 which is rockable in a sleeve 70 arranged on the inner sliding member 12. One end of the spindle 68 is engageable externally of the prop by a detachable handle 69 (FIG. 3) in order that the pump piston assembly may be reciprocated in the cylinder 40.

In the operation of the pump, with the prop initially in a completely collapsed condition, rotation of the spindle 68 causes the connecting rod 64 to move the smaller diameter pump piston 44 downwardly in the bore of the larger diameter piston 42, until such time as a spring 72 carried by the clevis 62 contacts the upper face of piston 42. Continued movement of the connecting rod 64 then moves both pistons 42 and 44 down the pump cylinder 40 to deliver hydraulic medium from that cylinder via a pump delivery valve 74 in the inner ram part 32 into the pressure chamber below the ram 26. When the movement of the spindle 68 and connecting rod 64 is reversed at the bottom of the delivery stroke, the smaller diameter piston 44 first rises in the bore of the large diameter piston 42, and then, when it reaches the top of said bore, lifts the piston 42 as well, until both pistons are arrested as the piston 42 contacts the neck ring 54. During this upward stroke, hydraulic medium is admitted into the pump cylinder 40 from the reservoir in the interior of the inner sliding member 12, through an annular space 76 between the ram parts 30 and 32, a passage 78 formed in the ram part 32, and a pump inlet valve 80. The movements described of the pump pistons 42 and 44 are continued, and thereby the volume of hydraulic medium admitted into the pressure chamber below the ram 26 is increased, causing the inner sliding member 12 to extend, until such time as the top cap 18 encounters resistance, as by commencing to support a load. The pressure of hydraulic medium in the pressure chamber then rises to a value such that manual effort applied to the spindle 68 is insufficient to move the larger diameter piston 42 when the pum delivery valve is opened and places the pressure chamber in communication with the pump cylinder 40, so that, at that stage, the larger diameter piston 42 remains held at the upper end of the cylinder 40 by the said pressure of hydraulic medium, and the pumping action thereafter consists simply of reciprocation of the smaller diameter piston 44 within the bore of piston 42. This pumping action of the smaller diameter piston 44 is continued until the pressure of the hydraulic medium in the pressure chamber attains a predetermined value at which the prop will support a desired load which may, for example, be of the order of five to ten tons. This predetermined value of pressure is governed by the valve 50, 52, of which it will be noted that the spring force urging the valve ball 52 on to the seat 50 is adjustable by means of an adjusting screw 51 threadedly engaged in the interior of the smaller diameter piston 44. The valve ball 52 will thus lift from the seat 50 when the pressure exceeds that determined by the valve spring adjustmerit, and further pumping strokes of the piston 44 will simply result in hydraulic medium being passed back to the reservoir through the piston interior and apertures 53 in the piston walls.

It is well recognized that, when a hydraulic prop has been set to sustain a predetermined maximum load, as described above, it is important to provide the pressure chamber with a yield valve or relief valve which will enable some of the hydraulic medium to escape from the pressure chamber in the event that the load exerted on the prop should increase, whereby to maintain the pressure of the hydraulic medium remaining in said chamber at a substantially constant value. For this purpose, the prop proposed by the invention provides a capsule 82 containing a suitable relief valve, the capsule 82 being fitted in a bore formed to receive the same in the inner ram part 32. The arrangement is such that hydraulic medium escaping from the pressure chamber through the yield valve is passed through lateral passages 91 and 92 in the inner part 32 of the ram, and thence into the annular passage 76 and from there back into the reservoir.

When it is desired to collapse the prop, as for removing it from a situation where it has been supporting a load, it is necessary firstly to remove the full applied load from the prop in order that the ram parts 30 and 32 may thereafter be separated from one another to permit subsequent rapid collapse of the inner sliding member 12 into the outer member 10. The inner ram part 32 is therefore provided with a stepped bore 84 wherein is received an unloading valve comprising a valve ball 86' resiliently urged against a valve seat 88 constituted by one of the steps in the bore 84, and a plunger 90 having one of its ends bearing against the valve ball 86 and its other end projecting slightly above the upper face of the ram part 32. Thus, as described below, the plunger 90 may be depressed by the larger diameter pump piston 42 to lift the valve ball 86 from seat 88, and thereby permit high pressure hydraulic medium to escape from the pressure chamber through the lateral passage 92 in the inner ram part 32, and thence through the annular passage 7 6' back into the reservoir. Thereafter, mutual separation of the ram parts 30 and 32 may readily be effected.

It will have been noted from the foregoing description that the hydraulic pump, the yield valve, unloading valve, and collapse means necessary to effect all the operations of a hydraulic prop, that is to say, extension, setting under desired load, unloading and collapse, are all included in/or carried by the inner part 32 of the ram 26. In this way, the invention makes it possible for all the functions mentioned to be controlled from a single point, that is, the spindle 68, by so dimensioning and arranging the connecting rod 64, crank arm 66, and the stroke of the pump pistons 42 and 44 that the said functions are all carried out in dependence upon the amount of the rotary displacement imparted to the spindle 68, away from a rest position of that spindle defined by the abutment of a stop 67 on the crank arm 66 against the wall of the sliding member 12. In this position of the spindle 68, the detachable arm 69 occupies an uppermost position, as shown in FIG. 3. Starting from a completely collapsed condition of the prop, therefore, depression of the handle 69 will cause the connecting rod 64 to reciprocate both the pump pistons in the pump cylinder 40, as already fully described, to extend the prop until a load is encountered by the top cap 18. Due to the large displacement of hydraulic medium thus effected, this extension is of a rapid nature, and enables the prop quickly to be located in a desired position, whilst since the said displacement is effected at low pressure, the prop not yet being under load, the spring 72 prevents a movement of the smaller diameter pump piston 44 into the bore of the larger diameter piston '42 sufiiciently large to allow the valve ball 52 to be unseated by the spigot 48. The spring rates of the spring 72 and of the spring urging the valve ball 86' on to its seat 88 are also so arranged that, during this low-pressure pumping stage, there is no danger of the plunger 90 being displaced by the piston 42 and unseating the valve ball 86, since immediately the piston 42 touches the plunger 90, a substantial resistance is felt to further movement of the handle 69, and such movement is forthwith reversed. The extent of movement of handle 69 during low-pressure pumping is over an are 71 of about 80", as shown in FIG. 3, this being arranged to accomplish a full stroke of the pistons 42 and 44 in the pump cylinder 40. Immediately the prop commences to support a load, and the piston 42 remains held at the upper end of the cylinder 40, the pumping action changes simply to reciprocation of the piston 44 within the piston 42, and the movement of the handle 69 required for this purpose is over an arc 73 of some 30. Continued reciprocation of the smaller diameter piston 44, by transferring on each stroke, smaller volumes of hydraulic medium at high pressure into the pressure chamber, then sets the prop to support the desired load, as determined by the value of pressure at which the valve ball 52 lifts. Thereafter, the pressure prevailing in the pressure chamber is governed, while the prop is in use, by the yield valve in the capsule 82. When it is desired to collapse the prop, the handle 69 is depressed to move the smaller diameter piston 44 against the resistance of the hydraulic medium present in the pump cylinder 40, and the valve ball 52 lifts to allow the hydraulic medium to flow through the interior of the piston 44 and the apertures 53 back into the reservoir. When the piston 44 reaches the bottom of its stroke in the bore of the piston 42, that is, when the handle 69 is at the bottom of the are 73 of FIG. 3, the spring 72 contacts the upper face of the latter piston, and on further depression of the handle 69, the spring 72 is compressed to allow a suflicient further movement of the piston 44 to a position where the spigot 48 unseats the valve ball 52. Both pistons 42 and 44 are then enabled to travel with very little resistance down the cylinder 40 as pressure on the handle 69 is maintained, the displaced hydraulic medium again flowing through the interior of piston 44 and out through the apertures 53. When both pistons 42 and 44 reach the bottom of the cylinder 40, the handle 69 then being at the bottom of the are 71 shown in FIG. 3, the prop is ready for initial unloading prior to complete collapsing of the sliding member 12 into the outer member 10. Unloading of the prop is accomplished by then exerting a further downward pressure on the handle 69, to cause the lower face of the piston 42 to contact and displace the plunger 90, thereby unseating the valve ball 86. Hydraulic medium then flows from the pressure chamber, past the valve ball 86 and through the passages 92 and 76 into the reservoir. As soon as the pressure of hydraulic medium in the pressure chamber has fallen to a suitable value, the handle 69 may be still further depressed, through an additional small arc 75 of about as shown in FIG. 3, to cause the piston 42 to bear on the inner ram part 32 and separate the two ram parts 30 and 32 against the action of the spring 60. The relatively wide spacing thereby created between the ram parts 30 and 32 then permits substantially unrestricted flow of hydraulic medium from the pressure chamber back into the reservoir, with consequent rapid collapse of the inner sliding member 12 into the outer member 10 of the prop.

The feature of the invention that the several elements controlling the various functions of the prop are carried by the ram 26 lends itself particularly to the provision of facilities for ready maintenance. For example, it will be noted in the construction shown in FIG. 1 that the bottom cap 14 is held in its position in the outer member 1! by means of a removable bolt 13 or by separate screws, and hence, it is a simple procedure by removing the bottom cap 14 following collapse of the inner member 12 into the outer member 11 to renew the hydraulic seal 23 or replace the yield valve capsule 82. This operation requires only that a retainer plate 29 be removed first and subsequently replaced; the plate 29 serves to retain the seal 28 and the valve springs of valves 74 and 86 in their respective positions.

However, since it can happen that, in use, the bolt 13 becomes damaged and cannot then readily be removed, it is preferred to secure the bottom cap 14 permanently to the outer tubular member 10, as by welding as shown in FIG. 4. In this case, the extraction of the whole ram and pump assembly is necessary for servicing purposes, and takes place from the upper end of the prop, by firstly removing a clamping ring which is secured around the upper end of the outer tubular member lltl, both to maintain in position a dirt-excluding seal 102, and also to locate the upper end of an outer protective cover 164. The ring 1% also retains in position, a cylindrical sleeve bearing 166 which is arranged between the tubular members 10 and 12 for accurately guiding the relative sliding movement between the two. As evident from FIG. 4, the spindle 63 which engages in the sleeve 70 is formed intermediate its ends with an annular groove 168, and when the spindle is in position within the sleeve, a part of this groove N8 is located within the interior of the inner tubular member 12. The sleeve is formed with a hole 119 through which is passed a split pin 112, and the engagement of the pin 112 in the groove 168 normally retains the spindle securely within the sleeve 70. As also shown in FIGS. 1 and 4, the spindle 68 is formed at its inner end face with a diametrical slot 114 for engaging over the crank arm 66, and is provided centrally of the slot 114 with an axially directed spigot 116 which passes through a co-operating hole 118 in the crank arm 66.

In the extraction of the ram and pump assembly, therefore, when the ring tea has been removed, the pump is operated by rocking the spindle 68, until all the hydraulic medium has been transferred from the reservoir into the pressure chamber. Thereafter, continued pumping causes air to enter the pressure chamber above the hydraulic medium, resulting in continued extension of the prop until such time a sthe ram 26 of the inner tubular member 12 encounters the sleeve bearing 106 between the two tubular members. The sleeve bearing 196 is pushed out from the outer tubular member 16 by the extension movement of the inner tubular member 12, and when this stage is reached, the inner tubular member itself may be completely removed from the outer member. Thus, on removal of the top cap 13 from the inner member, the split pin 112 may be taken out of the sleeve 70 housing the spindle 68, when the latter may be withdrawn from said sleeve, automatically disengaging itself at this time from the crank arm 66. Finally, by removing the threaded screws 34 securing the ram to the inner tubular member 12, said ram and the remaining elements which go to make up the control unit can be withdrawn completely from the inner member 12, and a complete replacement unit fitted by adopting the reverse procedure to that described.

Yet another feature of the prop of the invention which contributes to accessibility and servicing of the various working parts concerns the breather valve with which such props are provided to maintain the air space above the hydraulic medium in the reservoir at atmospheric pressure, irrespective of the movement of hydraulic medi um into and out of the reservoir. As shown in FIGS. 1 and 4, the prop has a breather valve comprising a valve housing 94 from which depends a freely movable pendular member 96. The valve housing 94 is a press fit within a central aperture of the closure plate 17 and is formed with a through passage including a valve seat (not shown). The end of the pendular member 96 within the valve housing 94 carries a valve member (not shown) which is spaced from said valve seat when the prop is in an up right position, thus allowing free communication between the interior of the reservoir and the interior of the extension 16, which in turn communicates with the external atmosphere. The arrangement is such, however, that Whenever the prop is tilted beyond a predetermined limit away from the vertical, the pendular member will close the valve member on to the seat, and prevent hydraulic medium from inadvertently escaping from the reservoir.

Since contamination of the breather valve is likely to occur under the arduous conditions in which props are em ployed, however, it is very desirable that such valves be readily accessible for cleaning. In the prop shown in FIG. 1, this is accomplished simply by unfastening the bolt 24, lifting out the tubular extension 16, and easing the breather valve out of its press fit in the closure plate 17. On reassembling, the bolt 24 will be seen to just bear against the top of the valve housing 94, to prevent the breather valve subsequently from being accidentally displaced from the plate 17.

As a further precaution against contamination of the breather valve, the upper end of the through passage in the valve housing 94 may open into an annular groove 98 formed externally around said housing, and said groove may have an air filter of annular form arranged therein. A preferred type of such filter according to the invention consists of a band or ring of spirally wound wire, with adjacent turns of the spiral positioned in very close spacing to one another.

We claim:

1. In a hydraulic support of the type comprising a pair of coaxially arranged tubular members engaged one within the other for relative sliding movement, a hydraulic ram detachably secured at the inner end of the inner tubular member and cooperating with the outer tubular member to define a pressure chamber for receiving a hydraulic medium under pressure, a hydraulic piston pump carried by the ram within the interior of the inner tubular member, said interior constituting a hydraulic medium reservoir, means accessible externally of the support and including a pump piston connecting rod for operating the pump to transfer hydraulic medium from the reservoir to the pressure chamber, and valve means for enabling hydraulic medium to return from the pressure chamber to the reservoir; the improvement wherein the pump operating means comprises a hollow cylindrical sleeve secured transversely to and extending within the interior of the upper end region of the inner tubular member, a rockable spindle journalled in said sleeve and having a portion engageable externally of said inner tubular member for enabling rocking motion to be imparted to said spindle, said spindle being formed with an annular groove intermediate its ends, said sleeve being formed intermediate its ends with a hole registering with said groove, a removable retaining pin passed through said hole to engage in said groove for retaining said spindle in said sleeve, a crank having one end pivotally secured to the upper end of said pump piston connecting rod, the inner end of said spindle being formed with a diametrical slot having said crank engaged therein, and an axially directed spigot extending from said inner end of said spindle and substantially centrally of said slot, said crank being formed at its other end with a bore fitting over said spigot.

2. In a hydraulic support of the type comprising a pair of coaxially arranged tubular members engaged one within the other for relative sliding movement, a hydraulic ram detachably secured at the inner end of the tubular member and co-operating with the outer tubular member to define a pressure chamber for receiving a hydraulic medium under pressure, a hydraulic piston pump carried by the ram within the interior of the inner tubular member, said interior constituting a hydraulic medium reservoir, means accessible externally of the support and including a pump piston connecting rod for operating the pump to transfer hydraulic medium from the reservoir to the pressure chamber, and valve means for enabling hydraulic medium to return from the pressure chamber to the reservoir; the improvement wherein the ram and the pump constitute an assembly comprising a two-part ram having an outer part detachably secured to the inner tubular member and an inner part engaging coaxially within and displaceable relative to said outer ram part with spring means for holding said ram parts normally in sealing relation with one another; a two-stage pump comprisnig a pump cylinder extending axially within the inner tubular member and secured to the rear of the inner ram part, a two-part pump piston slidable in said pump cylinder and including an axially bored outer piston part and a hollow inner piston part slidable therein, said inner piston part being pivotally secured to the lower end of said connecting rod; first passage means including a yield valve in said inner ram part for returning hydraulic medium from said pressure chamher to said reservoir whenever the pressure in said chamber exceeds a predetermined value; second passage means between said reservoir and said pressure chamber and including a plunger-operated unloading valve in said inner ram part, the operating plunger of said unloading valve projecting into the pump cylinder for depression by said pump piston to operate said unloading valve when said piston is advanced into abutment against said inner ram part, whereby said unloading valve permits an initial escape of hydraulic medium from said pressure chamber into said reservoir as a preliminary to collapsing of said support, further advance of said piston being arranged to displace said inner ram part away from said outer ram part thereby to create between said ram parts, a substantially free flow path for hydraulic medium between said pressure chamber and said reservoir for completing said collapse; and pump operating means comprising a hollow cylindrical sleeve secured transversely to and extending within the interior of th upper end region of the inner tubular member, a rockable spindle journaled in said sleeve and having a portion engageable externally of said inner tubular member for enabling rocking motion to be imparted said spindle, said spindle being formed with an annular groove intermediate its ends, said sleeve being formed intermediate its ends with a hole registering with said groove, a removable retaining pin passed through said hole to engage in said groove for retaining said spindle in said sleeve, and detachable connection means between the spindle and the upper, free end of the pump piston connecting rod for enabling reciprocation of said piston responsive to rocking motion of said spindle.

3. A support as set forth in claim 2, wherein said detachable connection means comprises a crank having one end pivotally secured to the connecting rod, the inner end of said spindle being formed with a diametrical slot having said crank engaged therein, and an axially directed spigot extending from said inner end of said spindle and substantially centrally of said slot, said crank being formed at its other end with a bore fitting over said spigot.

References Cited in the file of this patent UNITED STATES PATENTS 883,773 Ashmore Apr. 17, 1908 941,870 Gathmann Nov. 30, 1909 1,080,062 Hess Dec. 2, 1913 FOREIGN PATENTS 542,887 Belgium Dec. 15, 1955 1,180,410 France Dec. 29, 1958

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