Hydraulic and earth engineering – Earth treatment or control – Shoring – bracing – or cave-in prevention
Patent
1996-06-26
1998-02-24
Taylor, Dennis L.
Hydraulic and earth engineering
Earth treatment or control
Shoring, bracing, or cave-in prevention
2483543, 405288, E21D 1550
Patent
active
057205817
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
This invention relates to a support prop of the kind which involves a tube and a plunger.
PRIOR ART
Yieldable support props are described in South African patent 90/1985. These support props each consist of an outer tube with a flared mouth which accommodates a metal ring surrounding a plunger. The ring has serrations on its bore which engage the plunger. As a yielding load is applied to the prop, the plunger and the ring move downwardly into the outer tube whilst the outer tube is deformed by the ring.
In order to pre-load such a prior art support prop, a set of hydraulic jacks are positioned between the ring and a clamp removably clamped to the plunger. The jacks are connected to a portable hydraulic pump to cause them to extend and thus to set the prop in place at a predetermined load.
A disadvantage associated with this prior art support prop is that in practice difficulty, is encountered in pre-loading the prop in the manner described. In particular during pre-loading, relative movement between the outer tube and the plunger tends to occur resulting in a loss of the pre-load.
A desirable characteristic of a yieldable prop is that it should quickly reach a point at which it will yield at a substantially constant load. Furthermore the load required to cause the prop to yield must be capable of being predicted with a degree of certainty. If a yieldable prop does not yield at a substantially constant load or if the prop yields at unpredictable loads, the consequences can be catastrophic and loss of life and production may result. The prior art yieldable props have suffered from both these disadvantages.
OBJECTS OF THE INVENTION
It is an object of this invention to provide a support prop which can be preloaded in a manner which at least reduces the disadvantages associated with the prior art. It is a further object of this invention to provide a support prop which will yield with at least a degree of certainty.
SUMMARY OF THE INVENTION
According to the invention a support prop includes: within the flared mouth of the outer tube; prop between two surfaces by displacing the plunger relative to the outer tube.
The support prop may include a seal to prevent fluid from escaping between the plunger and the bore of the outer tube. The seal is preferably a floating cup seal.
An end cap may be secured to the end of the plunger located within the outer tube. A bearing portion which bears against the bore of the outer tube may be provided to locate the plunger within the outer tube to limit axial misalignment of the plunger relative to the outer tube. The bearing portion may be provided on the end cap of the plunger.
The deforming means may have an inner surface with gripping formations which are harder than the plunger so that the gripping formations can bite into the plunger to engage the plunger. The deforming means may have an outer surface with spaced recesses and outer tube contact zones located between the spaced recesses. The outer tube contact zones may taper from their upper ends towards their lower ends. The bottom end of the deforming means is preferably radiused.
At least pan of the bore of the outer metal tube may be coated with friction reducing means. In addition or alternatively the outer surface of the deforming means may be coated with friction reducing means. The friction reducing means may comprise any one of oil, polytetrafluoroethylene, molybdenum disulphide or graphite.
A pedestal is preferably provided inside the outer tube on which pedestal the plunger can seat when the plunger is fully retracted.
The plunger is preferably a tube.
An aperture may be provided in the sidewall of the outer tube through which aperture fluid can escape from the chamber if the plunger is displaced beyond the aperture in the direction of the flared mouth of the outer tube.
At least one marking may be provided on the outer surface of the plunger to indicate over extension or impending over extension of the plunger.
The inlet may be a male or a female coupling. The coupling may be located
REFERENCES:
patent: 2621631 (1952-12-01), Donty
patent: 4185940 (1980-01-01), Spies
patent: 4640650 (1987-02-01), Koppers et al.
patent: 5379566 (1995-01-01), Schworer
patent: 5400994 (1995-03-01), Shawwaf et al.
Bacon Michael S.
Greenwood Andrew T.
Hillier Allan W.
Spearing Anthony J.S.
Terblanche Ivan
Dorbyl Limited
Taylor Dennis L.
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