US2895454A

US2895454A - Props, especially for use in coal mines

Info

Publication number: US2895454A
Application number: US590185A
Authority: US
Inventors: Tebb Bernard; Perry Clarence Herbert
Original assignee: Mastabar Mining Equipment Co Ltd
Current assignee: Mastabar Mining Equipment Co Ltd
Priority date: 1955-06-10
Filing date: 1956-06-08
Publication date: 1959-07-21
Anticipated expiration: 1976-07-21
Also published as: GB793803A; GB802803A; DE1064907B; BE548513A; FR1151305A; DE1063554B; FR1162002A; BE553227A

Description

B. TEBB ETAL PROPS, ESPECIALLY FOR USE IN COAL MINES July 21, 1959 3 Sheets-Sheet 1 Filed June 8, 1956 IL 1 L? Inventor:

BERNARD TE-5B 0 w m W W A r. R w m M. A a

. July 21, 1,959 I B. TEBB ETAL 2,895,454

PROPS, ESPECIALLY FOR USE IN COAL MINES Filed Jun 8, l956 3 Sheets-Sheet 2 I Inven for, 4 /91?!) T565 ERBEIFT PERKY 85/? CMKENIE W; T 2 x- A ttore 31,6

2,895,454 PROPS, ESPECIALLY non USE IN COAL MINES Bernard Tebb, Swanland,

Hull, England, assignors ment Company Limited, company Application June 8, 1956, Serial No. 590,185 Claims priority, application Great Britain June 10, 1955 14 Claims. (Cl. 121-40) and Clarence Herbert Perry, to Mastabar Mining Equip- Hull, England, a British The present invention concerns hydraulic pit props for mine roof supporting or shoring purposes.

An object of the invention is to provide a prop of generally improved structure and performance which is especially suitable for filling the requirements in coal mines where, for example, a controlled roof collapse may be necessary.

Another object is to provide for effecting collapse of the hydraulic pit prop from a safe distance. i

A further object is to enable the collapsing pressure to be selected by an external adjustment on the prop.

To achieve the first of these objects the present invention provides a hydraulic prop having a rising characteristic as regards its load releasing behaviour. Suoh rising characteristic implies that an initial release will take place on the attainment of a minimum predetermined loading and that the loading to cause subsequent releases will increase with load displacement until the value of theload becomes equal to the maximumload sustaining capacity of the prop.

Frictional or mechanical props, which may be at a disadvantage compared With hydraulic props on account of greater weight or fire hazard, have indeed been constructed with rising characteristics; whereas hydraulic props have hitherto allowed release of the load at a substantially constant liquid pressure irrespective of load displacement, thus having a flat characteristic.

T According to the present invention therefore a rising characteristic hydraulic prop incorporates a liquid pressure relief valve adapted to open at a varaible pressure and a relief pressure adjuster actuated responsive to a function of load displacement. The adjuster preferably acts on the relief valve spring and may constitute or provide a displaceable spring adjustment or anchorage.

Thus the relief valve on a first portion of the prop may be urged towards its seat by a spring, for example in theform of a torsion bar anchored on the fulcrum of a lever constituting the adjuster, a second portion of the prop displaceable relative to the firstporti'on carrying a cam adapted on displacement occurring to swing the lever and thereby efiect rotation of the anchor end of the swing.

Instead of the adjuster being moved mechanically responsive to displacement it may be displaced hydraulically, for example, constituting part of a chamber of variable volume which is expanded by admission thereto of liquid discharged past the relief valve itself.

According to a further feature of the invention a torsion spring loading a relief valve or valves is anchored to a spring loaded member presenting an attachment for an external operating element such as a lanyard. Then on displacement of the member against its spring loading the relief valve loading may be reduced, so as to initiate collapse of the prop.

The position of the spring loading member is preferably adjustable, i.e. by a screwed stop or collar so as toenable the loading of thetorsion spring on the relief valve and hence the normal collapsing load to be varied.

The torsion spring may provide positive loading for one relief valve and secondary loading for a second relief valve.

The invention will be described further with reference to the accompanying drawings in which:

Fig. 1 is a medial vertical section of a hydraulic pit, prop constructed in accordance with the invention;

Fig. 2 is an elevation of the adjustable release control shown in Fig. 1

Fig. 3 is an enlarged fragmentary horizontal section on the line IlI--III of Fig. 1;

Fig. 4 is a part medial vertical section of a portion of an alternative form of hydraulic pit prop constructed in accordance with the invention;

Fig. 5 is a medial vertical section of a modification of the prop shown in Fig. 4;

Fig. 6 is a medial vertical section showing a further form ofhydraulic pit prop in accordance with the invention; i

Fig. 7 is a horizontal section on the line VIIVH of H Fig. 6; and

' Fig. 8 is a horizontal cross section on the line VIII- VIII of Fig. 6 certain parts being similar to those shown in Fig. 3.

In the drawings like reference numerals refer to like 1 parts.

In the prop shown in Figs. 1 to 3, embodying a mechanically displaced adjuster, an upper or first portion 11 includes a hollow piston or ram 12 attached at its lower end and received Within a cylinder forming the lower or second prop portion 14 fixed to the'base 15 of the prop. The upper telescopic member 11 is secured at its upper end by way of a collar 16 to an upper extension 17 which, at its upper end, is fixed to the head 18 of the prop.

The inverted piston head 12 includes a chamber 43 formed therewithin by a screwed plug 44 engaged in a threaded and counterbored inverted bore in the piston 12. The plug 44 is provided with an oil sealing or packing ring 4411, and its lower end is flanged so as to engage and retain an end plate 45 which serves: to retain an oil seal 13.. The chamber 43 communicates with the interior. of the upper telescopic member 11 which constitutes an oil reservoir, by way of a bore 47. A space 50, below the piston 12, within the telescopic member 14 communicates with the chamber 43 by way of a vertical bore 55 which runs into a horizontal bore 56. A ball relief valve "57, displaceable within the bore 56 is adapted, in its closed position, to prevent entry of oil from the space 50 to the chamber 43.

The ball 57 is urged towards its seating 58 by a pres sure bar 62 projecting radially from near the lower end of a vertically extending spring torsion bar 61 suitably guided at or near both its ends for rotary movement relative to the piston 12. The upper end of the torsion bar 61 is attachedat one end of an arm 64 and thus by reason of its guiding this end of the bar 61 with the arm 64 constitutes a lever fulcrum. The other end of the arm 64 projects outwardly through a slot 80 in the wall of the upper extension 17 of the upper prop to permit of adjustment of the initial spring pressure.

An inlet connection (not shown) is provided to the space 50, thus with any suitable preloading of the prop in its initial or maximum height condition, liquid may be pumped into this space 50 of the cylinder.

In the alternative form of construction shown in Fig. 4

hydraulic displacement of the adjuster is efiected by making the adjuster in the form of a floating piston 81 displaceable within the piston skirt or hollow cylindrical part of. the upper portion 11 of the prop. This. floating piston -81 then forms the upper wall of a chamber 82 of variable volume constituted by the space within the lower .part of the upper portion of the prop, i.e. between the floating piston 81 and the upper surface of the inverted head of the prop piston 12. A relief valve 83 is arranged to discharge liquid into the variable volume chamber 82 with the result that the floating piston 81 is moved upwardly relative to the piston head- '12. The relief valve 83 is disposed within the piston headI 12. and is adapted to move downwardly to open and is loadedby a coiled tension spring 84 anchored at its upper end' to the floating piston 81. Thusafter discharge of. liquid from the relief valve 83 the floating piston 81 rises and: increased tensional spring. pressure is applied to the valve 83.

Alternatively, as shown in Fig. 5, a coiled compression spring 85 is contained in the space 86 between the-upper, most interior part of the upper portion of theprop and. the floating piston 81, its lower end resting on an abutment 87 which bears downwardly on an upwardly opening relief valve 83 in the. floating piston 81. This valve 83 is connected to a passage 88 through the propwpiston head 12 by way of a high pressure coiled flexible con duit 89. Hence on liquid being discharged by the valve 83, downwardly into the chamber 82 below the floating piston 81, the floating piston 81 rises carrying the relief valve 83 with it. This upward displacement. of the floating piston 81 or adjuster provides a relative displacement of the abutment 87 of the upper end of the coiled compression spring 85 which is thereby compressed so as toincrease the pressure exerted on the relief valve 83.

In both these hydraulic arrangements at low pressure subsidiary relief valve 90 discharging upwardly is provided to relieve excessive pressure developing below the floating piston 81. External connections both to the prop, or high pressure cylinder and to the chamber of variable volume or low pressure cylinder are provided.

to enable the prop to be appropriately preloadedon its. initial installation. I t

In the embodiment shown in Figs. 6 to 8,, a hydraulic pit prop includes an upper telescopic member 11 having a piston 12 attached to its lower end. The piston carriesa sealing ring 13 adapted to seal the piston in liquid tight manner within a cylinder constituted by. a lower telescopic member 14 fixed to the base 15 of the prop.

The upper telescopic member is secured at its upper end: by way of a collar 16 to an upper extension 17 which at its upper end is fixed to the head 18 of the prop.

A pump cylinder 21 is fixed in a screwed bore. atthe topof the piston 12. In this cylinder a large piston 22.

is displaceable. The large piston -22 is axiallybored to."

accommodate a piston rod 23 and counterbored to form. a smaller diameter pump cylinder 24 within which-a small piston 25 fixed to the lower end of the'piston rod 23 is displaceable. The upper end of the piston rod is fixed in. av clevis 26 which is urge-d upwardly relative to the large pump piston 22 by a coiled compression spring 27. A connecting rod 28 is pivoted. at its lower end to the clevis by means of a pin 29, and its upper end. is pivotally connected to a crank 30 adapted to-berotated by application of a suitable hand tool to the squared outer end 31. of its shaft 32 whichisjournall'edvina socket 33 secured in the wall of tlreextension: 17. Suitable oil sealing or pacldng ringsare provided/on the pump-pistons 22 and 25-and on the 'pump' crankshaft 32.

The working space of the pump cylinders corn'munia cates by Way of an inlet ball valve-"41' and abore' 42' with an enclosed chamber 43*formed within thefp'rop the upper telescopic member 11 which constitutes an oil reservoir, by way of a bore 47. The Working space of the pump pistons communicates by way of a bore 48, the outlet valve 46 and an aperture 49 in the plate 45 with a space 50, below the piston 12, within the lower telescopic'member 14.

The space 50 communicates with the chamber 43 by way of a vertical bore 51 which runs into a horizontal bore 52. A release valve 53 is urged on to a seating, which results from a change in diameter of bore 52, by a coiled compression spring 54. Space 50 further communicates with the chamber 43 by way of a vertical bore 55 which runs into a horizontal bore 56. A relief valve. 57 slidable within bore 56, is urged against a seating 58 within bore-56 by means of a-vertically extending torsion bar spring 61 which passes downwardly through.

striker 63 adapted to bear against the valve 53 on rotation of torsion bar spring 61.

The. upper end of the torsion spring is fixed to an arm 64 which is pivotally connected to a link 65 which. in

turn is pivotally connected to a lug 66 of a plunger 67. This plunger is displaceable in a cylindrical housing 68 containing a spring69 which bears against an adjustable abutment plug 70 and urges the plunger in aninward direction. The shank of the plunger passes outwardly through a bore in the plug 70 and is screwed into an eye 71. A lanyard for effecting release of the prop may be passed through the aperture in the eye 71; or alternatively, as shown a rod 72 is fitted into this aperture and arranged to engage a wedge ended cam or release bar 73. This bar 73 is adjustable in a vertical direction relative to the lower telescopic prop member 14 by means of a clamp 74 so as to enable the cam profile to cause outward displacement of the plunger to a required extent in a given relative position of the two

telescopic members

11 and 14 of the prop.

In operation the prop is extended by manually imparting rotation to the shaft 31 using an appropriate brace or other tool engaged on the squared end of this shaft. Rotation of the shaft 31 causes the crank 30 to impart vertical small piston 25. This results in a rapid displacement of oil from the reservoir, through the bore 47 into chamber 43' and through the bore 42- and past valve 41 into the pump cylinder 21 and thence through the bore 48, past vaiCe 46 and through the aperture 49 into the space 50,

with the result that the upper member 11 is forced outwardl'y', thereby extending the prop. When, however, the head 18 bears against the mine roof the pressure within the space rises rapidly and further rotation of the shaft 31 causes the small piston 25 to move relative to the large piston 22 as soon as the upward thrust due to liquid pressure on the large piston 22 exceeds the downward thrust exerted upon it by the spring, 27. Continued pumping action is then efiected by reciprocation of the small piston 25 which thus enables a preloading pressure to be applied with relatively small liquid displacement to the space 50 and thereby to the prop as a whole.

Torsion bar spring 61 is initially adjusted to main.-

' tain valve 57 against seating 58 by means of adjustable plug 7 0; Excessive pressure within sp'ace50 unseats valve 57 and oil flows from space 50 to the reservoir via

bores

55, 56, chamber 43 and bore 47 causing collapse of the prop (or less rapid extension). The unseating of valve 57 is assisted by outward movement of plunger 67 causing rotation of torsion bar spring 61 and arm 62. Further outward movement of plunger 67 causes striker 63 to unseat valve 53 and oil flowing from space 50 to the reservoir is provided with an additional path via bores 51, 52, chamber 43 and bore 47.

Outward movement of plunger 67 is elfeoted by pulling on the eye 71 by means of a lanyard or other external operating element or is effected automatically during extension of the prop by means of the wedge ended cam 73. It will be appreciated that the Wedge ended cam will also cause inward movement of plunger 67 during collapse of the prop, thus progressively increasing the resistance of the prop to collapse.

We claim:

1. In a hydraulically extensible pit prop having a rising characteristic, hydraulic load sustaining means, pressure relief means adapted on opening to relieve hydraulic pressure within said load sustaining means, and relief pressure adjusting means bearing on said pressure relief means and defining a range of relief pressures at which said pressure relief means is permitted to open, said adjusting means being operable responsive to a function of load displacement to render said relief pressure continuously variable within said range during extension and contraction of said prop.

2. A hydraulically extensible pit prop comprising an upper telescopic member, a lower telescopic member, one of said members acting as a piston and being displaceable in a hydraulic cylinder constituted by the other of said members, a liquid pressure relief valve communicating with said cylinder and adapted to open to relieve hydraulic pressure therein, and relief pressure adjusting means bearing on said relief valve and defining a range of relief pressures at which said valve is permitted to open, said adjusting means being operable responsive to a function of load displacement to render said relief pressure continuously variable within said range during relative move ment between said telescopic members.

3. In a hydraulically extensible pit prop having first and second relatively displaceable portions, a relief valve on said first portion, spring means for urging said relief valve into its closed condition, an adjusting means carried by said first portion and constituting a displaceable anchorage for said spring means, and cam means on said second portion adapted to displace said adjusting means and thereby vary the pressure exerted by said spring means on said relief valve responsive to the relative positions of said first and second portions.

4. In a hydraulically extensible pit prop having first and second relatively displaceable portions, a relief valve on said first portion, a torsion bar spring for urging said relief valve into its closed condition, a lever carried by said first portion and connected at its fulcrum to said torsion bar spring so as to constitute a displaceable anchorage for said spring, and cam means on said second portion adapted to displace said lever and thereby vary the pressure exerted by said torsion bar spring on said relief valve responsive to the relative positions of said first and second portions.

. In a hydraulically extensible pit prop having first and second relatively displaceable portions, a relief valve on said first portion, spring means for urging said relief valve into its closed condition, a displaceable wall in said first portion defining therein a chamber of variable volume, said wall being displaced in accordance with the amount of liquid contained in said chamber and constituting a displaceable anchorage for said spring means, and conduit means for feeding hydraulic liquid discharged by said relief valve into said chamber to thereby vary the pressure exerted on the relief valve by said spring means responsive to the relative positions of said first and second portions.

6. In a hydraulically extensible pit prop formed with a reservoir for hydraulic fluid and a working chamber into which said fluid is intended to be urged under pressure to extend said prop, a torsion bar spring, at least one fluid pressure controlling valve communicating with said working chamber loaded by means of said torsion bar spring, said valve controlling the discharge of pressure fluid from said working chamber, a spring loaded displaceable member to which said torsion bar spring is anchored, means acting on said displaceable member for displacing said member between fixed limits during extension and contraction of said prop, the displacement of said member thereby varying between upper and lower limits, the load exerted by said torsion spring on said controlling valve, and an external operating means attached externally to said spring loaded displaceable member and by which said member is displaced to cause the load exerted on the valve by the torsion bar spring to be removed for collapse of the prop.

7. A structure according to claim 6, in which said spring-loaded member is adjustable.

8. A structure according to claim 6, in which said spring-loaded member is adjustable by means of a screwed stop.

9. A structure according to claim 6 in which the fluid pressure control valve is a pressure relief valve, and said structure further comprises at least one further relief valve, the torsion bar spring providing positive loading for one relief valve, and negative loading for the other relief valve.

10. In a hydraulically extensible pit prop having an upper portion and a lower portion, said upper portion being formed with a chamber constituting a reservoir for hydraulic fluid and said lower portion being formed with a chamber constituting a work chamber into which hydraulic fluid is intended to be urged to extend the prop, a piston displaceable in the chamber presented by said lower prop portion, a relief valve carried by said piston and controlling communication between said lower chamber and that presented by the upper prop portion, a vertically extending torsion bar spring having an upper end and a lower end, guide means adjacent to and guiding said ends for rotation of said torsion bar spring relative to said upper prop portion, means for adjustably anchoring the upper end of said spring against rotation relative to said upper prop portion, and an arm fixed to said spring at the lower end thereof and adapted to transmit the spring pressure to said valve to urge it towards its closed condition in opposition to the fluid pressure in the lower chamber.

11. A structure according to claim 10 including a second arm fixed to the upper end of the spring perpendicularly thereto, the upper prop portion being slotted to permit said second arm to extend horizontally outwardly therethrough, and a cam-bar carried by the lower prop portion and adapted to bear on said second arm and vary its angular position relative to the prop in accordance with the relative positions of said upper and lower prop portions.

12. In a hydraulically extensible pit prop having two relatively displaceable portions, a hydraulic pressure relief valve carried by one of said portions, a torsion spring loading said valve, an anchorage member connected to said spring and displaceably mounted on said portion carrying the relief valve, an external operating member for displacement 'of said anchorage member and an attachment for said external operating member whereby said valve may be caused to open by displacement of said anchorage member and consequential variation in the loading applied to said valve by said torsion spring.

13-. In a hydraulically extensible pit prop having a continuously. varying rising characteristic as regards its load releasing behaviour, hydraulic load sustaining means, pressure relief means adapted on opening to relieve hydraulic pressure within said load sustaining means, and hydraulically displaced relief pressure adjusting means for varying the hydraulic pressure at which said relief means opens responsive to a function of the amount of hydraulic liquid discharged by said relief means.

14. A hydraulically extensible pit prop comprising an upper telescopic member, a lower telescopic member, one

of saidmembers acting as a piston and being displaceable in a hydraulic cylinder constituted by the other of said members, a liquid pressure relief valve communicating with said cylinder and adapted to open at a variable pressure, and hydraulically displaced relief pressure adjusting means acting on said relief valve responsive to a function of the amount of hydraulic liquid discharged by said valve whereby to provide a rising characteristic in the load-displacement behaviour of the prop.

References Cited in the file ofthis patent UNITED STATES PATENTS 2,618,122 Gratzmuller Nov. 18, 1952 2,621,631 Dowty ,Dec. 11, 1952 2,638,075 Towler May 12, 1953 2,699,180 Frye Jan. 11, 1955 2,713,773 Sutton July 26, 1955