US3712572A

US3712572A - Mechanical extension devices for hydraulic or other props

Info

Publication number: US3712572A
Application number: US00036640A
Authority: US
Inventors: K Groetschel
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-05-16
Filing date: 1970-05-12
Publication date: 1973-01-23
Anticipated expiration: 1990-01-23
Also published as: GB1313846A; DE2021155A1; AU1509370A

Abstract

A stilt for use with a pit prop comprising an outer tubular member which at one end receives an end portion of the prop and which contains either a variable number of spacer pieces or a variable height spacer piece, and the tubular member has an entry at its end remote from the prop to enable spacer pieces to be inserted and removed or the variable height spacer piece adjusted, such stilt being provided either at the lower end or upper end of the prop which may be incorporated in a selfadvancing roof support comprising a base, a plurality of such props and a roof-engaging superstructure.

Description

Waited States Patent 91 Groetschel [54] MECHANICAL EXTENSION DEVICES FOR HYDRAULIC OR OTHER PROPS [76] Inventor: Karl M. Groetschel, Stolzestrasse 44, Bochum, Germany [22] Filed: May 12, 1970 [21] Appl. No: 36,640

[ 30] Foreign Application Priority Data [58] Field 01 Search...248/346, 354 H, 354 R, 354 S, 248/356, 357; 254/92, 98, 100,101, 134, 133.1, DIG. l

.[56] References Cited UNITED STATES PATENTS 1,513,252 10/1924 Lampert ..254/133,l

1,479,090 1/1924 Slonecker.... ..254/98 396,321 1/1889 Baird .,..248/354 S UX 224,499 2/1880 Williams ..254/98 1 Jan.23,1973

2,925,981 2/1960 Wilson et a1. ..248/354 R FOREIGN PATENTS OR APPLlCATlONS Primary ExaminerWilliam H. Schultz Attorney-Spencer & Kaye [57] ABSTRACT A stilt for use with a pit prop comprising an outer tubular member which at one end receives an end portion of the prop and which contains either a variable number of spacer pieces or a variable height spacer piece, and the tubular member has an entry at its end remote from the prop to enable spacer pieces to be inserted and removed or the variable height spacer piece adjusted, such stilt being provided either atthe lower end or upper end of the prop which may be incorporated in a self-advancing roof support comprising a base, a plurality of such props and a roof-engaging superstructure.

17 Claims, 11 Drawing Figures PATENTEDJMI 23 I975 SHEET 1 [1F 2 INIEMQR Kori Moria Graeme; ,4hdl/V 5 BY ATTORNEYS.

MECHANICAL EXTENSION DEVICES FOR HYDRAULIC OR OTHER PROPS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a mechanical extension device (herein called a stilt) for, or in association with, a hydraulic or other pit prop.

In underground mine workings in which such pit props are used there is considerable variation in the floor to roof height when may occur in consequence of variable seam thickness of the coal or other mineral substance being mined, and it frequently occurs that even when using the maximum lift or stroke of the prop, the length of the latter is insufficient to enable it to perform its proper roof supporting function at places where the floor to roof height is increased above that normally encountered in the working as a whole.

2. Description of the Prior Art In an endeavor to overcome this problem it has been proposed to provide, in association with a pit prop, a one-piece body to be fitted to the lower end of the prop. This expedient, however, has the disadvantage that it provides only one value of incremental increase of the effective length of the prop and is of such form that it can be secured to, and removed from, the prop only with a considerable expenditure of manual effort, and furthermore constitutes an encumberance to transport in the mine working owing principally to the size of the body. Moreover complications are entailed where a plurality of such bodies are provided of respectively differing heights appropriate for use at places presenting respectively different fioor to roof heights.

There have also be proposals to provide a stilt for assembly with the lower end of a prop comprising a plurality of spacer pieces assembled in a stack beneath the lower end of the prop and pivoted to an upright rod offset laterally with respect to the prop axis, so that they can be swung about the rod into a position beneath the prop or withdrawn from such position.

The disadvantage, however, of this proposal is the low degree of stability presented by the stack of spacer pieces. Further, there are difficulties in applying this proposal to a form of mine roof support which is increasingly being brought into use in place of individual pit props, namely a self-advancing roof support comprising a base, a plurality of props thereon, and a roofengaging superstructure carried by the props, and traction means for advancing the support.

Yet another prop extension device that has been proposed for incorporating in a self-advancing roof support as above described is one which comprises an externally screw-threaded tubular member closed at its lower end to form a socket for receiving the lower portion of the prop and itself inserted into a further tubular member mounted within one of the prop housings of the base of the support, a nut member co-operatively engaged with the external thread of the first said tubular member resting on the upper end of the second tubular member to provide, in effect, a supplementary screw jack by means of which the height of the prop can be varied. In the conditions encountered in underground mine workings, especially coal mines, this proposal has the disadvantage that it is exposed to damage by way of dirt and falling rock impinging on the external screw thread, and also entails relatively high manufacturing cost having regard to the relatively large diameter of the screw thread which must be accurately cut. To obtain adequate strength the tubular member having the screw thread must have a relatively large external diameter and the second tubular member'must, therefore, be made still larger in diameter, these factors contributing materially to the cost of both such components.

SUMMARY OF THE INVENTION The object of the present invention is to provide a mechanical extension device or stilt for, or in association with, a hydraulic or other pit prop whether used singly or as part of a self-advancing roof support, and which is of simple and reliable construction and capable of economic manufacture, the stilt also providing good stability and being of compact sturdy form. The present invention resides in the provision for, or in association with, a hydraulic or other pit prop of a stilt comprising means defining an inner vertical spacer of variable height, means defining an outer container for receiving said spacer in its interior and having a lateral wall surrounding said spacer to provide lateral location or support therefore around said spacer, entry means in said lateral wall compatible with maintainance of said lateral location or support but affording access to said interior for effecting changes of height of said spacer.

In the preferred form the stilt comprises a tubular member open at one of its ends to receive one end of an associated prop, said spacer is of such size relatively to the internal cross-sectional dimensions presented by said tubular member to have only small lateral clearance with respect to said tubular member, said entry means is situated adjacent to the other end of said tubular member and is of a height which is small compared with the total length of said tubular member.

The opening in the tubular member may thus be of a height sufficient to admit of insertion of only one spacer piece at a time into the tubular member and at positions above the opening the tubular member thus presents an internal surface providing all round lateral location or support to any spacer pieces containedtherein projecting above the upper end of the opening.

The spacer may comprise one or more spacer pieces forming a stack in said tubular member, the number of spacer pieces determining the height presented by the spacer, said entry being of a height sufficient only to admit of the insertion of one of said spacer pieces at a time, at positions between said entry and said one end of said tubular member the latter presenting an internal surface providing lateral location or support for any of said spacer pieces contained therein at positions around the entire perimeter of each of said spacer pieces.

Although nominally of fixed or constant height, one or more of the spacer pieces may be so formed or constructed as to be collapsible in response to the application of a downward load exceeding a predetermined value, for example exceeding the yield load of the associated prop. This is an additional safeguard, in that when a prop has contracted to the maximum extent, due to application thereto from the roof of the mine working of a load exceeding the yield load, damage to the prop and possibly other relatively expensive components of a self-advancing roof support in which such prop may be incorporated are avoided. The collapsed spacer piece is a comparatively inexpensive component.

Alternatively, I may utilize in the stilt one or more of the variable height spacer pieces, each of which may incorporate components which are movable relatively to each other in an upward direction and adjusting mechanism controlling the relative positions of said components and capable of bearing the downward load applied to the spacer piece when in use. A particularly convenient form of adjustment mechanism comprises a wedge mechanism which comprises a wedge element having its ends presented laterally of the spacer piece and in this case the tubular member may be formed to include openings at opposite ends of the wedge element respectively, and adjacent to the lower end of the tubular member through which the wedge element can be driven in one direction or the other to adjust the height of the spacer piece.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example, with reference to the accompanying drawings wherein:

FIG. 1 is a view in front elevation, partly in cross-section, of a portion of a self-advancing roof support incorporating a prop equipped with one embodiment of stilt in accordance with the invention;

FIG. 2 is a plane view of the parts shown in FIG. 1 with the prop removed;

FIG. 3 is a view in side elevation and partly in crosssection of the parts shown in FIG. 1;

FIG. 4 is a fragmentary view showing only the prop and stilt device of FIG. 1 to 3 with a plurality of spacer pieces inserted to raise the level of the prop;

FIG. 5 is a view in front elevation of one form of spacer piece which may be incorporated in a stilt inaccordance with the invention;

FIG. 6 is a view in side elevation of a further form of spacer piece;

FIG. 7 is a plane view of still a further form of spacer piece;

FIG. 8 is a view in side elevation of still a further form of spacer piece;

FIG. 9 is a fragmentary view in side elevation and partly in cross-section of a further embodiment of stilt in accordance with the invention;

FIG. 10 is a view in side elevation, partly in cross-section, of still a, further form of spacer piece; and

FIG. 11 is a fragmentary view in side elevation and partly in cross-section illustrating a further embodiment .of stilt in accordance with the invention wherein the stilt is assembled with the upper end of the associated prop.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring firstly to the embodiment of stilt shown in FIGS. 1 to 4, the stilt is shown applied to a prop 10 incorporated in a self-advancing roof support which comprises a base, a plurality of props similar to the prop 10 at positions spaced apart thereon, a superstructure (not shown) carried by the props at their upper ends for engaging and supporting the roof, and a traction means for advancing the support. Typically each of the props is supported in an upstanding housing 11 on the base and such housing contains a means for maintaining the prop in an upright position as shown whilst permitting it to be tilted to a controlled extent in response to lateral loads applied to the superstructure. These means comprise four blocks or bodies 12 of rubber or other elastic material which may each be of elongated form spanning one pair of opposed sides of the housing 11 which is of square configuration as seen in FIG. 2, one such block or body being arranged on each of four sides of the prop.

The lower part of the housing 11 is secured to, and extends upwardly from, one of the floor-engaging members of the base formed, for example, of laterally spaced box-section bars 13 connected by plates 14, the upper of which has a centering ring 15 receiving and providing lateral location for the stilt 16 provided in ac cordance with the invention.

The stilt comprises a tubular member 17 which may, and preferably does, project upwardly for some distance above the upper end of the housing 11 and is centered by the rubber blocks or bodies 12, as mentioned, at its upper end and by the ring 15 at the lower end.

The tubular member 17 is of such internal diameter as to receive the lower end portion of the prop 10 as an easy sliding fit but without substantial lateral clearance. In the interior of the tubular member 17 is a spacer which may be formed of one or more spacer pieces 18 which are inserted between the lower end of the prop l0 and a supporting surface constituted either by a bottom wall 19 of the tubular member 17 (if the latter is closed at its lower end) or possibly by the upper plate 14. In some cases, however, it may be convenient for the tubular member 17 to be open at its bottom end and for the spacer piece or the lowest of them to rest on the floor of the mine working.

The spacer pieces are of square form as seen in plan (FIG. 2) and of dimensions such that they are circumscribed by the interior surface of the tubular member 17 with only slight lateral clearance, that is to say the diagonals of the spacer pieces 18 are slightly less then the internal diameter of the tubular member.

This ensures that each spacer piece is located, that is positioned, laterally more or less precisely by the interior surface of the tubular member and that when a stack of spacer pieces are utilized the tubular member provides lateral stability preventing the stack collapsing or bulging in the interior of the tubular member.

Conveniently, but not essentially, the spacer pieces are each of a height equal, or approximately equal, to the lengths of their sides as viewed in plan (so as to be of cubic form or approximately so). To enable the spacer pieces to be inserted into, and withdrawn from, the tubular member, the latter is formed adjacent to its lower end with an entry in the form of a generally rectangular opening 20. The opening 20 has a height which is only a little greater than the height of each spacer piece individually, as will be evident more particularly from FIG. 4, and the width of the opening 20 is a little greater than the corresponding dimension of each spacer piece, that is the length of the side. The

opening 20 thus occupies only a little more than one quarter of the circumference of the tubular member and the latter is not seriously weakened. Moreover, it will be evident that a spacer piece occupying the lowermost position is located by engagement of at least two of its corners with the internal surface of the tubular member, and that any spacer piece which is raised to project above the upper boundary of the opening is located against lateral displacement in all directions relative to the axis of the tubular member.

It will, of course, be evident that other shapes of spacer piece may be utilized as viewed in plan, for example rectangular section. In this case the width of the opening 20 could be reduced still further, for example it will be as little as one half the internal diameter of the tubular member.

The spacer piece may be of hollow form and conveniently constituted by pieces cut off from a box-section bar. To enable them conveniently to be inserted and manipulated, lifter members 21 are provided, these being in the form of rods 22 equipped at their outer ends with handles 23. The spacer pieces are formed with holes 24 through which the lifter members can be passed. Extending from the upper boundary of the opening 20 is an extension opening 25 in the form of a slot having a width-slightly exceeding the cross-sectional dimensions of the rods 22 of the lifter members and formed above its lower end at a distance at least equal to the height of each spacer piece with a lateral branch 26, the lower boundary of which forms a ledge or shoulder on which the rod of a lifter member can be raised to support the associated spacer piece at an elevated position leaving a vacancy beneath it for the insertion of a further piece.

The housing 11 of the base of the roof support is formed with a sufficiently large opening 27 to enable the lifter members and spacer pieces to be manipulated as required. Conveniently the interspace within the housing 11 between this and the tubular member 17 forms a storage chamber for accommodation of spacer pieces, as seen particularly in FIG. 1.

At a position diametrically opposite the extension opening 25 a matching opening may be formed in the tubular member so that, as seen particularly in FIG. 3, a rod 22 of a lifter member can be supported at two positions thereby permitting the handle to be released whilst a further spacer piece is introduced into the vacant space beneath the elevated spacer piece.

' Various alternative forms of spacer piece are illustrated in FIGS. 5 to 8 to which reference will now be made The space piece of FIG. 5 formed from a piece cut off from box-section bar such as that normally used for the construction of roof supporting bars includes a stop means in the form of an upstanding stud, bolt or other projection 28 welded or otherwise secured to the bottom wall and of such length as to afford a clearance space 29 between its upper end and the top wall of the spacer piece.

When subjected to a predetermined load in excess of that capable of being borne by the narrowest sections 30 of the side walls, collapse will take place limited by engagement of the top wall with the upper end of the projection 28.

As seen in FIG. 6 -a generally similar spacer piece may be modified by formation of holes 31 through its side walls 30 to provide collapse at a predetermined downward load. This load should be greater than the yield load of the prop. It may exceed this value by about 50 percent of the value of which other components of the prop support are superior in load bearing capacity to the prop itself. Thus, in the event of the support becoming jammed between the roof and floor, the spacer pieces by collapsing in the manner indicated, that is by permanent deformation or fracture, provide additional security against destruction of relatively costly components of the support, including the props after the latter have become fully contracted.

In the further form of spacer piece shown in FIG. 7, upper and lower square or rectangular plates 32 are connected by an intermediate cylindrical wall 33 through which holes may be bored as seen at 34 for the purpose already indicated. A stop means in the form of an upstanding bolt or projection 35 is also provided for operation in a manner similar to the projection 2d. The square or rectangular plates 32 engage the inner surface of the tubular member 17 at their comers in a manner similar to that already described to provide lateral location and stability.

It will be evident that each of the forms of spacer piece shown in FIGS. 5 to 7 includes a cavity which enables the inner end of a lifter member to be inserted, this being, for example, the open end of the spacer piece of FIG. 5, the open end or the holes 31 of the spacer piece of FIG. 6, and the holes 34 of the spacer piece of FIG. 7.

In FIG. 8 the spacer piece therein depicted is of inverted cup-shape. This form of space piece 40 is in tended to be made of brittle material which becomes fragmented under downward loaded exceeding a predetermined value. The hollow interior 41 provides space for the accommodation of parts broken off. It is also possible to bring about deliberate fracture of the piece 40, for example by hammering or smashing same through the opening 20 at the particular time at which it is required to release a jammed roof support or prop.

It is contemplated that the spacer pieces of FIGS. 5 to 7 would be made of a metal capable of plastic deformation to provide the required yield, for example steel, whilst the spacer element shown in FIG. 8 may be made of a brittle material, either metal or a non-metallic material such as glass or a ceramic material.

Referring now to the alternative embodiment shown in FIG. 9, parts corresponding to those already described are designated by like reference numerals with the prefix I and the preceding description is to be deemed to apply.

In this embodiment a wedge element 142 is provided for operation between a lower component 143 of a v spacer piece and an upper component 144 thereof, the

latter having an inclined lower face matching the inclined face of the wedge element. A housing 145 slotted to permit of transverse passage of the wedge surrounds the lower part of the component 144 which has a flange or head 147 engaging the upper end of the housing 145 when the wedge is knocked out to prevent the inclined face of the upper component bearing against the horizontal, upwardly presented, face at the upper end of the lower component 143. The tubular member 117 may be formed with a further opening 146 adjacent to one end of the wedge, the other end of the wedge being accessible through the opening 120. The opening 120 may be of sufficient size to permit of insertion of the spacer piece either in assembled form or one component at a time, whereas the opening 146 is only large enough to permit of operation of the wedge therethrough. Alternatively the spacer piece could be inserted through the top of the tubular member 117 before insertion of the prop.

A further fonn of spacer piece is illustrated in FIG. 10 designed to yield by a substantial distance in the case of application of downward load exceeding the predetermined value (corresponding to the yield load of the associated prop).

In this construction the upper component 247 engages in the interior of a hollow cage-like or cup-shape lower component 248 provided with a cotter means 249. The cotter means may be in the form of a relatively thin plate having lateral projections 250 which rest in holes or slots in the side walls of the lower component and which are sheared form the main body or central portion of the plate when a load exceeding the predetermined value is applied. Openings 251 at the lower end of the lower component are provided for removal of any sheared parts in the interior of the lower component. The cotter means 249 may alternatively be in the form of a transverse bolt or pin. A flange or head 252 on the upper component will engage the upper edge 253 of the lower component at the limit of downward travel.

It is contemplated that in cases where a plurality of spacer pieces are used, as is shown, for example, in FIG. 4, these will normally be all of one kind and of nominally fixed height. However, under certain conditions spacer pieces incorporating means for adjusting the height, for example as shown in FIG. 9, may be combined with those shown in FIGS. 5 to 8 and 10. In this case application to a load exceeding a predetermined value will provide yield by virtue of the permanent deformation or fragmentation of certain of the spacer pieces whilst the adjustment mechanism may be operated subsequently to release a prop or support from a jammed position.

Although the spacer pieces are located laterallyby the internal member I may provide formations on the spacer pieces which supplement lateral location. For example, a projection could be provided at the underside of each spacer piece to engage in a recess formed at the upper side of the piece next beneath it. Alternatively the centering or locating formations could be constituted by vertically inter-engaging parts at the peripheries of the spacer pieces or loose pins engaging in bores or like formations.

A further embodiment of the invention is illustrated in FIG. 11 wherein parts corresponding to those previously described are designated by like numerals of reference with the prefix 3, and the preceding description is to be deemed to apply.

In this embodiment the stilt 316 is assembled with the upper end of an associated prop 310.

The tubular member 317 has its upper end portion received in a cavity or socket 360 which is presented downwardly at the underside of one of the members 361 of a roof-engaging superstructure of a self-advancing roof support, the remaining parts, namely the base and traction means, of which are omitted for clarity.

The tubular member 317 is connected to the member 361 by connecting means such as one or two links of chains 362, so that if the superstructure remains in an elevated position, by virtue of continued extension of other props of the support when the illustrated prop 310 is contracted, the tubular member 317 also remains in the raised position suspended from the member 361, while the upper end portion of the prop 310 descends.

Spacer pieces 318 contained in the tubular member 317 thus descend leaving a free space opposite to the entry 320 which allows additional spacer pieces to be inserted as required.

For removing spacer pieces the prop 310 can be extended until the topmost spacer piece is in a position just opposite to the entry 320 without being under load, whereupon it can be removed either directly or by means of a tool such as the lifter member already described and illustrated in the embodiment of FIGS. 1 to 4.

Iclaim:

1. A prop stilt comprising:

a. an outer tubular member open at one end and having a lateral wall of internal cross-sectional form and dimensions are to receive said prop as a close sliding fit;

b. a plurality of spacer pieces each of a size to be closely enclosed by said lateral wall superposed in a stack between said prop and the other end of said ,tubular member; and entry means in said lateral wall adjacent to said other end of said tubular member and of a height sufficient only to admit of the insertion of said spacer pieces singly, said tubular member being of circular form as viewed in plan, each of said spacer pieces being of non-circular form so selected as to present at least one transverse dimension less than the intemal diameter of said tubular member, said entry is of a width less than the internal diameter of said tubular member but greater than said dimension of said spacer pieces the shape of each of said spacer pieces is such that, upon insertion into said tubular member, said spacer piece will contact same at a plurality of positions spaced apart angularly about the axis of said tubular member to provide the required lateral location or support.

2. A stilt according to claim 1 wherein each of said spacer pieces is a. of polygonal form as viewed in plan and of dimensions to be circumscribed by the internal surface of said tubular member,

b. presents at least one pair of opposite parallel sides spaced apart by a distance less than the width of said entry in said tubular member.

3. A stilt according to claim 2 wherein each of said spacer pieces is of square form as viewed in plan having a diagonal dimension just less than the internal diameter of said tubular member to provide the requisite working clearance to prevent jamming of said spacer piece during insertion into said tubular member, and to allow movement of said spacer piece along said tubular member when a stack of said spacer pieces is inserted into said tubular members while preserving lateral stability of said stack.

4. A stilt according to claim 3 wherein said entry in said tubular member extends circumferentially of said tubular member for a distance just exceeding one quarter of the circumference of said tubular member.

5. A prop stilt comprising:

a. an outer tubular member open at one end and having a lateral wall of internal cross-sectional form and dimensions as to receive said prop as a close sliding fit, said one end of said tubular member is adapted to receive the lower end of the associated P p;

b. a plurality of spacer pieces each of a size to be closely enclosed by said lateral wall superposed in a stack between said prop and the other end of said tubular member;

c. entry means in said lateral wall adjacent to said other end of said tubular member and of a height sufficient only to admit of the insertion of said spacer pieces singly; and

. a lifter member having means engageable with that one of said spacer pieces in said tubular member situated opposite said entry to support said spacer piece, and any of said spacer pieces above it, during movement of said lifter member from a lowered position to a raised position through a distance such as to enable a further spacer piece to be inserted through said entry beneath said cooperative spacer piece and lifter member, said tubular member having has means defining a ledge to support said lifter member in said raised position.

6. A stilt according to claim 5 wherein:

a. said lifter member comprises an elongated rod-like member,

b. each of said spacer pieces is formed with at least one cavity to receive an end portion of said lifter member,

0. the remainder of said lifter member is adapted to protrude from said tubular member to an external position enabling it to be lifted to raise the spacer piece cooperate therewith.

7. A stilt according to claim 6 wherein:

a. said tubular member has an upwardly extending opening leading from the upper boundary of said entry,

b. said upwardly extending opening and said lifter member are relatively dimensioned to enable said lifter member to move upwardly in said opening with a portion of said lifter member disposed in the interior of said tubular member supporting one of said spacer pieces, and a further portion of said lifter member protruding externally from said tubular member.

8. A stilt according to claim 7 wherein said upwardly extending opening has a lateral boundary having an upwardly presented ledge or shoulder at a position above the upper boundary of said entry by a distance at least equal to the height of each of said spacer pieces.

9. A stilt according to claim 8 wherein said tubular member has a further similar upwardly extending opening formed therein at a position opposite that which extends from the upper boundary of said entry whereby said lifter member can be supported at diametrically opposed locations on correspondingly upwardly presented ledges or shoulders of said openings respectively.

10. A prop stilt comprising:

a. an outer tubular member open at one end and having a lateral wall of internal cross-sectional form and dimensions as to receive said prop as a close sliding fit;

b. a plurality of spacer pieces each of a size to be closely enclosed by said lateral wall superposed in a stack between said prop and the other end of said tubular member; and

c. entry means in said lateral wall adjacent to said other end of said tubular member and of a height sufficient only to admit of the insertion of said spacer pieces singly, at least one of said spacer pieces including a hollow body having side walls of a thickness selected to establish vertical collapse of said spacer piece in respect of loading thereof in a direction longitudinally of said stilt exceeding a predetermined value.

- 11. A stilt according to claim 10 wherein said side walls are apertured to present a cross-sectional area in a horizontal cross-sectional plane such that said side walls will undergo collapse in response to application of said predetermined load.

12. A stilt according to claim 10 wherein said hollow body contains stop means for limiting the extent of vertical collapse of said body.

13. A prop stilt, comprising:

a. an outer tubular member open at one end and having a lateral wall of internal cross-sectional form and dimensions as to receive a prop as a close sliding fit;

. a plurality of spacer pieces each of size to be closely enclosed by said lateral wall superposed in a stack between such prop and the other end of said tubular member; and

0. entry means in said lateral wall adjacent to said other end of said tubular member and having a height slightly greater than that of each spacer piece for permitting the insertion of only one said spacer piece at a time, and of a width less than any internal cross-sectional dimension of said tubular member, said spacer pieces each having at least one dimension which is less than the width of said entry means.

14. A stilt according to claim 13 wherein said tubular member has an end wall at said other end.

15. A stilt according to claim 13 wherein said lateral side wall is continuous both circumferentially and axially between said one end and a region bordering said entry, which region has an axial dimension of the same order as the height of said entry.

16 A prop stilt comprising:

0. entry means in said lateral wall adjacent to said other end of said tubular member and of a height sufficient only to admit of the insertion of said spacer pieces singly, said lateral wall being continuous both circumferentially and axially between said one end and a region bordering said entry,

which region has an axial dimension of the same order as the height of said entry, within said region said tubular member having at most'a pair of narrow axially extending slots at diametrically opposed positions each of a width which is small compared with the dimension of said entry measured circumferentially of said tubular member, said slots enabling a rod-like lifter to be inserted into and moved axially along the tubular member for lifting said spacer pieces.

17. A stilt according to claim 13 in combination with

Claims

1. A prop stilt comprising: a. an outer tubular member open at one end and having a lateral wall of internal cross-sectional form and dimensions are to receive said prop as a close sliding fit; b. a plurality of spacer pieces each of a size to be closely enclosed by said lateral wall superposed in a stack between said prop and the other end of said tubular member; and entry means in said lateral wall adjacent to said other end of said tubular member and of a height sufficient only to admit of the insertion of said spacer pieces singly, said tubular member being of circular form as viewed in plan, each of said spacer pieces being of non-circular form so selected as to present at least one transverse dimension less than the internal diameter of said tubular member, said entry is of a width less than the internal diameter of said tubular member but greater than said dimension of said spacer pieces the shape of each of said spacer pieces is such that, upon insertion into said tubular member, said spacer piece will contact same at a plurality of positions spaced apart angularly about the axis of said tubular member to provide the required lateral location or support.

2. A stilt according to claim 1 wherein each of said spacer pieces is a. of polygonal form as viewed in plan and of dimensions to be circumscribed by the internal surface of said tubular member, b. presents at least one pair of opposite parallel sides spaced apart by a distance less than the width of said entry in said tubular member.

5. A prop stilt comprising: a. an outer tubular member open at one end and having a lateral wall of internal cross-sectional form and dimensions as to receive said prop as a close sliding fit, said one end of said tubular member is adapted to receive the lower end of the associated prop; b. a plurality of spacer pieces each of a size to be closely enclosed by said lateral wall superposed in a stack between said prop and the other end of said tubular member; c. entry means in said lateral wall adjacent to said other end of said tubular member and of a height sufficient only to admit of the insertion of said spacer pieces singly; and d. a lifter member having means engageable with that one of said spacer pieces in said tubular member situated opposite said entry to support said spacer piece, and any of said spacer pieces above it, during movement of said lifter member from a lowered position to a raised position through a distance such as to enable a further spacer piece to be inserted through said entry beneath said cooperative spacer piece and lifter member, said tubular member having has means defining a ledge to support said lifter member in said raised position.

6. A stilt according to claim 5 wherein: a. said lifter member comprises an elongated rod-like member, b. each of said spacer pieces is formed with at least one cavity to receive an end portion of said lifter member, c. the remainder of said lifter member is adapted to protrude from said tubular member to an external position enabling it to be lifted to raise the spacer piece cooperate therewith.

7. A stilt according to claim 6 wherein: a. said tubular member has an upwardly extending opening leading from the upper boundary of said entry, b. said upwardly extending opening and said lifter member are relatively dimensioned to enable said lifter member to move upwardly in said opening with a portion of said lifter member disposed in the interior of said tubular member supporting one of said spacer pieces, and a further portion of said lifter member protruding externally from said tubular member.

10. A prop stilt comprising: a. an outer tubular member open at one end and having a lateral wall of internal cross-sectional form and dimensions as to receive said prop as a close sliding fit; b. a plurality of spacer pieces each of a size to be closely enclosed by said lateral wall superposed in a stack between said prop and the other end of said tubular member; and c. entry means in said lateral wall adjacent to said other end of said tubular member and of a height sufficient only to admit of the insertion of said spacer pieces singly, at least one of said spacer pieces including a hollow body having side walls of a thickness selected to establish vertical collapse of said spacer piece in respect of loading thereof in a direction longitudinally of said stilt exceeding a predetermined value.

11. A stilt according to claim 10 wherein said side walls are apertured to present a cross-sectional area in a horizontal cross-sectional plane such that said side walls will undergo collapse in response to application of said predetermined load.

13. A prop stilt, comprising: a. an outer tubular member open at one end and having a lateral wall of internal cross-sectional form and dimensions as to receive a prop as a close sliding fit; b. a plurality of spacer pieces each of size to be closely enclosed by said lateral wall superposed in a stack between such prop and the other end of said tubular member; and c. entry means in said lateral wall adjacent to said other end of said tubular member and having a height slightly greater than that of each spacer piece for permitting the insertion of only one said spacer piece at a time, and of a width less than any internal cross-sectional dimension of said tubular member, said spacer pieces each having at least one dimension which is less than the width of said entry means.

15. A stilt according to claim 13 wherein said lateral side wall is continuous both circumferentially and axially between said one end and a region bordering said entry, which region has an axial dimension of the same order as the height of said entry. 16 A prop stilt comprising: a. an outer tubular member open at one end and having a lateral wall of internal cross-sectional form and dimensions as to receive said prop as a close sliding fit; b. a plurality of spacer pieces each of a size to be closely enclosed by said lateral wall superposed in a stack between said prop and the other end of said tubular member; and c. entry means in said lateral wall adjacent to said other end of said tubular member and of a height sufficient only to admit of the insertion of said spacer pieces singly, said lateral wall being continuous both circumferentially and axially between said one end and a region bordering said entry, which region has an axial dimension of the same order as the height of said entry, within said region said tubular member having at most a pair of narrow axially extending slots at diametrically opposed positions each of a width which is small compared with the dimension of said entry measured circumferentially of said tubular member, said slots enabling a rod-like lifter to be inserted into and moved axially along the tubular member for lifting said spacer pieces.

17. A stilt according to claim 13 in combination with a prop, said prop having one end portion received in said tubular member of said stilt with the remainder of said prop projecting from said open end of said tubular member, said tubular member having internal cross-sectional dimensions such as to receive said end portion of said prop as a sliding fit without substantial lateral clearance, and said prop itself including components movable relatively to extend and contract the prop.