US3119309A

US3119309A - Cylinder and piston ram assemblies

Info

Publication number: US3119309A
Application number: US159056A
Authority: US
Inventors: Tebb Bernard; Perry Clarence Herbert
Original assignee: Mastabar Mining Equipment Co Ltd
Current assignee: Mastabar Mining Equipment Co Ltd
Priority date: 1957-07-30
Filing date: 1961-12-13
Publication date: 1964-01-28
Anticipated expiration: 1981-01-28
Also published as: BE569915A; DE1114456B; GB894292A; US2959922A; FR1200691A

Description

B. TEBB ETAL CYLINDER AND PISTON RAM ASSEMBLIES Jan. 28, 1964 Filed Dec. 13, 1961 2 Sheets-Sheet 1 INVENTORS BE N/m a 1638 CLAREN HER/95A? PERRY BY M W PM A TToKJyE vs Jan. 28, 1964 TEBB ETAL 3,119,309

CYLINDER AND PISTON RAM ASSEMBLIES M 6321M, ATTORNEYS INVENTOR:

United States Patent 3,119,309 CYLHNDER AND PISTON RAM ASSEMBLIES Bernard Tenb, Swaziland, and Ciarence Herbert Perry,

Hull, England, assignors to Mastabar Mining Equipment Company Limited, Hull, England, a British company Filed Dec. 13, 1961, Ser. No. 159,656 Claims priority, application Great Britain Dec. 22, 1960 Claims. (Cl. 91-422) This invention concerns cylinder and piston ram assemblies of the type which include a pair of coaxially arranged tubular members with one of said members comprising a ram slidable within the other member, the inner tubular member constituting a reservoir for h draulic medium and the outer member co-operating with said ram to define a hydraulic pressure chamber.

In many assemblies of this type, a hydraulic main seal of substantially U-section is arranged between the ram and the outer tubular member in order to prevent hydra lic medium in the pressure chamber from leaking past the ram. When the hydraulic medium in the chamber is under pressure, it acts itself to urge the sealing lips of the seal against the co-operating surface regions of the ram and the outer tubular member, whilst in the absence of any significant hydraulic pressure in the pressure chamber, the sealing lips are arranged to be an interference fit with the said surface regions. Such an interference fit may be provided, for example, by imparting a degree of pre-loading to the sealing lips.

The existence of this interference fit between the seal, the ram and the outer tubular member, however, can resuit in the application to the ram of a frictional loading such that, when it is desired to collapse or contract the support and some or all of the pressure is relieved from the pressure chamber, the resulting frictional resistance prevents a free fall of the ram within the outer tubular member.

The invention seeks to provide a cylinder and piston ram assembly wherein this disadvantage is avoided.

According to the present invention, in a cylinder and piston ram assembly of the type described and wherein the ram carries a hydraulic main seal presenting a pair of spaced annular sealing lips resting respectively against the ram and the outer tubular member, the ram is made in two coaxially arranged parts normally maintained in hydraulically sealed engagement with one another but having the inner ram part movable axially away from the outer ram part for creating a substantial fluid flow path between said ram parts whereby to enable said support to be collapsed from an extended condition, the hydraulic main seal being carried by the outer ram part, and spreader means engaging between said sealing lips are provided and are displaceable, responsive to movement of said inner ram part, for urging said lips mutually apart and respectively against said outer ram part and said outer tubular member whenever the two ram parts are brought into their normal hydraulically sealed relation.

The spreader means is preferably an annular ring engaged between the sealing lips, and such ring may be of circular or oval section, or it may be of a wedgeshaped section, in which case the diverging walls of the wedge section may be outwardly curved away from one another in order to provide the ring with an enlarged outer head portion.

Preferably, the inner ram part carries an inverted annular cap having a peripheral rim which is arranged to press against the spreader ring when the two ram parts are engaged together, and thereby cause the sealing lips to be spread apart and into their sealing co-operation with the outer tubular member and outer ram part.

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

FIG. 1 is a central, longitudinal section through a hydraulic pit prop embodying the invention,

FIG. 2 is a similar section, to an enlarged scale, of the lower end of the prop, and

FIGS. 3 and 4 inclusive are sectional details of a number of seal and spreader ring combinations.

Referring firstly to FIGS. 1 and 2, the prop shown therein comprises a pair of tubular members it) and 12, of which the upper or inner member 12 is telescopically engaged within the lower or outer member 11). The bottom end of the outer member 10 is closed by a bottom cap or foot 14 having a peripheral 0-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 29 which embraces the two and which is welded to member 12 at 22. A bolt 24 passes through the sleeve 2% 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 25 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 cham ber into which, by means of a two-stage piston pump generally designated 40 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. The pump 40 is operable, through a connecting rod 64 and crank 66, by angular reciprocation from externally of the prop, of a spindle 68 rockably journalled in a housing 70 carried by the inner tubular member 12 of the prop. Admission of hydraulic medium into the pressure chamber effects 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 but normally held in engagement by a spring 60. The outer part 3%) 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. For the purpose of enabling the prop to be collapsed from an extended condition, the two pump pistons are arranged to be capable of being depressed in the pump cylinder beyond their normal pumping stroke, when they come to bear on the inner ram part 32 to displace it against the action of the spring 60, thus creating a substantial fluid flow passage for hydraulic medium from the pressure chamber to the reservoir. The ram 26 may also conveniently be arranged to carry the pump delivery valve 74 together with any convenient construction of pressure relief valve 82 and initial pressure unloading valve 86. These valves are retained in their respective position in the ram part 32 by means of an inverted cap 27 secured to said ram part.

It will be noted more especially from FIG. 2, that the hydraulic main seal 28 has a pair of mutually spaced and generally concentric sealing lips 50 and 52., of which the lip 50 rests against the outer ram part 30 whilst the lip 52 rests against the internal surface of the outer tubular member 10 of the prop. Between the

lips

50 and 52 is arranged a spreader ring 54 and the annular peripheral rim 56 of the cap 27 is of a length such that, when the ram part 32 is engaged against the ram part 30, the rim 56 bears on the spreader ring 54 to urge it still further between the two sealing lips, which are thereby forced further apart and respectively pressed firmly against the ram part 30 and tubular member 19. Proper hydraulic sealing of the pressure chamber is thus assured, even when the hydraulic medium in said chamber is under little or no pressure. On the other hand, when the inner ram part 32 is displaced to allow the prop to collapse or contract from an extended position, the rim 56 is moved off the spreader ring 54, so that no positive force is applied to the

lips

50 and 52, either by way of preloading or otherwise, to maintain them frictionally against the outer ram part 30 and the member 10. Therefore, the ram is able to move freely within the member 10, and this contributes towards proper operation and a more rapid collapse of the prop.

Two spreader ring and hydraulic main seal combinations are shown by way of example in FIGS. 3 and 4. FIG. 3 shows a spreader ring 53 of simple circular section, whilst FIG. 4 shows a ring 55 of wedge-like section.

We claim:

1. In a cylinder and piston ram assembly of the type comprising a pair of coaxially arranged tubular members with one of said members including a ram slidable within the other member, the inner member constituting a reservoir for hydraulic medium and the outer member co-operating with said ram to define a hydraulic pressure chamber, and a hydraulic main seal on said ram and presenting a pair of spaced, annular sealing lips for engaging respectively against the ram and the outer tubular member, the improvement comprising a spreader member between the sealing lips of said main seal, and wherein said ram comprises coaxially arranged, separable inner and outer ram parts normally maintained in hydraulically sealed engagement with one another, the inner ram part being movable axially away from the outer ram part, and said inner ram part co-operating with said spreader member to displace said spreader member for urging said sealing lips mutually apart and respectively against said outer tubular member and said outer ram part whenever the two ram parts are brought into their normal hydraulically sealed engagement with one another.

2. A cylinder and piston ram assembly as set forth in claim 1, further comprising an inverted annular cap on said inner ram part and a peripheral rim on said cap and directed towards said spreader member for pressing against said spreader member when the two ram parts are engaged together.

3. A cylinder and piston ram assembly as set forth in claim 1, wherein said spreader member is an annular ring engaged between the sealing lips.

4. A cylinder and piston ram assembly as set forth in claim 3, wherein said ring is of circular section.

5. A cylinder and piston ram assembly as set forth in claim 4, wherein said ring is of wedge-shaped section.

References Cited in the file of this patent UNITED STATES PATENTS 2,713,773 Sutton July 26, 1955 2,851,011 Chasser Sept. 9, 1958 2,895,454 Tebb et al July 21, 1959 2,959,922 Tebb et a1 Nov. 15, 1960

Claims

1. IN A CYLINDER AND PISTON RAM ASSEMBLY OF THE TYPE COMPRISING A PAIR OF COAXIALLY ARRANGED TUBULAR MEMBERS WITH ONE OF SAID MEMBERS INCLUDING A RAM SLIDABLE WITHIN THE OTHER MEMBER, THE INNER MEMBER CONSTITUTING A RESERVOIR FOR HYDRAULIC MEDIUM AND THE OUTER MEMBER CO-OPERATING WITH SAID RAM TO DEFINE A HYDRAULIC PRESSURE CHAMBER, AND A HYDRAULIC MAIN SEAL ON SAID RAM AND PRESENTING A PAIR OF SPACED, ANNULAR SEALING LIPS FOR ENGAGING RESPECTIVELY AGAINST THE RAM AND THE OUTER TUBULAR MEMBER, THE IMPROVEMENT COMPRISING A SPREADER MEMBER BETWEEN THE SEALING LIPS OF SAID MAIN SEAL, AND WHEREIN SAID RAM COMPRISES COAXIALLY ARRANGED, SEPARABLE INNER AND OUTER RAM PARTS NORMALLY MAINTAINED IN HYDRAULICALLY SEALED ENGAGEMENT WITH ONE ANOTHER, THE INNER RAM PART BEING MOVABLE AXIALLY AWAY FROM THE OUTER RAM PART, AND SAID INNER RAM PART CO-OPERATING WITH SAID SPREADER MEMBER TO DISPLACE SAID SPREADER MEMBER FOR URGING SAID SEALING LIPS MUTUALLY APART AND RESPECTIVELY AGAINST SAID OUTER TUBULAR MEMBER AND SAID OUTER