US2621631A

US2621631A - Telescopic hydraulic mine roof support

Info

Publication number: US2621631A
Application number: US58949A
Authority: US
Inventors: George H Dowty
Original assignee: Dowty Equipment Ltd
Current assignee: Dowty Equipment Ltd
Priority date: 1948-01-12
Filing date: 1948-11-08
Publication date: 1952-12-16
Anticipated expiration: 1969-12-16
Also published as: DE808225C; NL76043C; BE486663A; FR69104E; FR978701A

Description

Dec. 16, 1952 G. H. DOWTY a B J Inventor 6202 15 /7 Don 777 A ttorn e ys Patented Dec. 16, 1952 TELESCOPIC HYDRAULIC MINE R SUPPORT George H. Dowty, Cheltenham, England, assignor to Dowty Equipment Limited, Cheltenham,

England Application November 8, 1948, Serial No. 58,949 In Great Britain January 12, 1948 9 Claims. (01. 121' 40) This invention relates to hydraulically actuat- I ed telescopic struts intended primarily for use as props in shoring up ceiling sections in mines.

The invention is concerned with that type of strut or prop which comprises a ram, usually hollow to constitute a liquid reservoir, which acts as a plunger in an upright external cylinder which below the ram constitutes a pressure chamber, so that extension can be effected by pumping pressure fluid from the reservoir into the pressure chamber, and contraction can be effected by relieving or venting the pressure in such pressure chamber back to the reservoir by way of a valvecontrolled return duct. Contraction may occur automatically when the roof weight exceeds a predetermined weight, and whether or not contraction is automatic, it must occur under manual control when it is desired to dislodge and remove the prop.

According to the present invention, contraction whether automatically or manually effected occurs by opening of a single valve, which is ordinarily biased to closed position but which is so connected to an external prop-handling member that a pull upon the latter from a safe distance will open the valve. Continuation of the same pull acts, through a first lost-motion connection, to pull aside or drag away the prop. A biasing force, which may be the one which biases the valve to close, or a different one, serves to maintain the prop-handling member in a given relationship to the props casing and to the first lost-motion connection, such that that member must be pulled in a manner to open the valve and to bottom the lost-motion connection before it is effective to drag away the prop. The connection of thevalve to the prop-handling member is preferably arranged, through a second lost-motion connection, which not only supplements the action of the first lost-motion connection in allowing automatic opening of the valve for relief without corresponding movement of the prop-handling member from that given relationship, in the event pressure within the return duct exceeds a predetermined pressure, but has the further advantage that a blow on exterior valve-operating parts can not be transmitted to the valve itself, to damage or to jam it under the rough treatment to which it is necessarily subjected in use. By enabling the single valve to function automatically as a relief valve and manually as a return or unloading valve, by 10- eating the valve in the upper portion of the easing, for movement transversely thereof, and by locating the prop-handling member in close relationship to the valve, and by insuring that the valve can not be damaged or jammed by external forces, certain advantages occur in the dislodgement of the prop by a pull from a distance upon the prop-handling member, all as will appear in detail hereinafter. Moreover, as the condition of the prop or strut'at the time withdrawal is desired is generally such that the pressure of the actuating fluid acting on the valve and tending to unseat it will substantially balance the force acting on the valve by the control member and tending to seat it, the magnitude of the pull on the control member necessary to bring about contraction of the prop or strut is very small indeed.

It is preferred to form the control member in two parts with the second lost-motion connection between them whereby the relief valve and its seating are not subject to shocks caused by inward blows directed against the external part of the control member. As a further protection to the valve the external part of the control member associated with the valve is preferably enshrouded by a rigid shield extending out from the ram.

A prop or strut in accordance with the invention can very conveniently be removed from a position of support by attaching a cord or cable to the outer end of the control member and by pulling the cord or cable firstly to relieve the pressure in the chamber below the ram and secondly to cause the prop or strut to topple over about its lower end. The operator can thus 'remove the prop orstrut while standing a safe distance away from the supported area, and he can remove the fallen prop or strut by dragging it endwise towards him. Its construction to these ends is a very important safety consideration in a pit prop.

In order that the invention may be more clearly understood and more readily carried into efiect, one embodiment of pit prop in accordance with the invention will now be described by Way of example with reference to the accompanying drawings, wherein:

Figure 1 is an axial sectional view of the upper end of the pit prop, and Figure 2 is a similar View of the lower end thereof, being in effect an axial continuation of Figure 1;

Figure 3 is a perspective view of the upper end of the prop, illustrating particularly the prophandling member, and

Figure 4 is a detail, in side elevation, and partly broken away, of the first lost-motion connecting means, between the prop-handling means and the casing.

The prop shown comprises a hollow tubular ram I which is closed at its upper end 2 and is slidable at its lower end telescopically within an outer cylinder 3 closed by a foot piece 4. The lower end of the hollow ram I mounts a c1osure disc which is glanded at 6 to the inner surface of the cylinder 3. The closure disc 5 is rigid with a co-axial tube I which extends for a short distance upwards into the ram to form the cylinder for the piston 8 of a reciprocating pump. The piston 8 has a connecting rod 9 extending upwards through the ram to where it is pivotally connected to the pin II) of a crank II which can be oscillated between stops from the outside of the ram I by a detachable handle (not shown) engaging the square-section end of the crankshaft I2. The piston 8 and the closure disc 5 have appropriate non-return valves I3 and I4 respectively whereby reciprocatidn of the piston 8 causes actuating fluid to be transferred from the interior of the ram I through the valve I I into the cylinder space below the ram I.

Just below the upper end of the ram I there extends transversely across the ram, rigidly connected thereto, a generally tubular housing I5 for a relief valve. The housing I5 has a transverse partition I6 situated within the ram, which partition I5 is formed with a co-axial passage II leading into a radial passage I8 which is in communication with the cylinder space below the ram I by means of a fixed tube I9 extending down from the partition I6 and through the closure disc 5 at th bottom end of the ram. A ball valve co-operates with the seating formed by the passage I! and is pressed against the seating by a piston member 2|, which in eifect is part of the valve, which is glanded at 22 to the inner surface of the housing I5 and is pressed against the ball 2!] by a spring 23 which bears at one end against the piston 2| and at the other end against an annular abutment 24 which is externally threaded and screwed a selected amount into the outer end of the housing I5. The piston 2| is rigid with an apertured co-axial cup 25 having within the cup the head of a bolt 25 which extends out through the cup and is screwed into a control member 2'! which extends through the annular abutment 24 to the outside of the ram. The control member 2'! and bolt 26 are in effect integral. The thickness of the head of the bolt is less than the depth of the cup 25 so E that there is lost-motion connection (referred to above as the second lost-motion connection) between the control member 27 and the piston 2!. A cross pin 28 extends through the control member 2'! and with clearance through holes 29 in the housing I5. This clearance is part of the first lost-motion connection, referred to above. A handling loop 30 is attached to the ends of the cross pin 28, and ordinarily hangs downwardly therefrom. The part of the housing I5 which is external of the ram I serves as a protection for the control member 2?. If, despite this precaution, the control member 21 should be subjected to any blows, the lost-motion will ensure that these will not be imparted to the ball valve 20.

At the opposite end of the housin 25 there is provided an air valve 3| of rubber or like material. This valve 3% can be depressed from the outside against a spring 32 to permit air to pass into the upper part of the ram through three equally spaced passages of which one is shown in the drawingat 33. The valve 3! is hollow and has a breather slit 3d through which air may escape from within the ram. The valve 3I thus ensures that the air pressure in the upper part of the ram will not depart substantially from atmospheric pressure.

It is intended that the ram will be filled with hydraulic fluid to the level indicated at 35. This level will be difierent for props of different lengths. The filling operation can be achieved by unscrewing the end plug 33 and by tilting the prop so that the hydraulic fluid can be poured into th ram through two of the passages 33 whilst, air is escaping through the other passage 33. When the requisite amount of fluid has been poured into the ram, the plug 33 with the air valve therein is replaced.

It will be seen that the end closures 2 and Q at the upper and lower ends respectively of the prop extend in the radial sense to form flanges. These increase the areas of support, and if the prop should topple over, act to safeguard the tubes I and 3.

In use it is frequently necessary to tap the lower part of the prop with a hammer in order to adjust its vertical disposition. Also the prop is liable to receive shocks and blows from other sources. It will be realized that it is desirable to avoid denting or distorting the tube .3 which forms the cylinder for the glanded closure disc 5 of the inner tube or ram I and it is therefore proposed to provide around the tube 3 a protection in the form of a spaced outer tube 31 which is secured to the flange of the foot piece 4 and is resiliently located at its upper end by a collar 38 of rubber or the like. If desired, however, the tube 37 may be secured rigidly to the ring 39 which retains the seal 43. Again the tube 3 may be protected by an outer covering of rubber which extends down to the flange of the end closure 4.

One convenient method of assembling the various parts of the prop is as follows:

The housing I5 is first passed through diametrically opposite bores in the thickened upper part 4| of the ram I. Next the pressure relief tube I9 is entered into its radial bore in the housing I5 and welded to the housing. The housing I5 is then correctly positioned radially of the thickened part H of the ram and welded to it at 42.

After this the upper end closure 2 is welded in position. This completes one unit subject to assembly of the relief and air valve mechanismv Next the piston 8 is secured to its connecting rod 9 and the rod 9 and crankshaft are assembled in the short housing 43. This assembly is passed through the tube I and the housing 43 is entered in the bore formed to receive it in the tube I. The housing 43 is then Welded to the tube. The first unit is now passed down, into the tube I and is secured by welding at 44. Next the bearing sleeve 45 together with the packing MI and the ring 39 are slipped along the tube I from its lower end. The closure disc 5 with the tube I welded thereto is entered into the lower end of the tube I so that the tube I receives the piston 8 and the tube I9 is received in the corresponding bore in the disc 5. The disc 5 can now be welded to the lower end of the tube I at 46, and the tube I9 welded to the disc 5. After the gland 6 and the valve I4 have been assembled on the closure disc 5, the prop is completed by threading over the tube I the assembly comprising the tube 3, the foot piece 4 and the protecting tube 37. The sleeve 38 is of course positioned around the upper end of the protecting tube 3! and the ring 39 for the gland 40 is welded to the upper end of the tube 3.

When the prop is to support a ceiling section, the pump is operated to transfer actuating fluid from the reservoir within the hollow ram into the 'cylinderfspace below the ram. The prop will then extend and be clampedbetween the floor and ceiling. If the roof weight should exceed a predetermined weight due to the tendency for the roof to sag, the liquid acting on the

relief valve

20, 2| will unseat the valve against the influence of the spring 23 acting through the pis: ton member on the valve. The prop will thus accommodate itself to the increasing roof weight. When it is desired to Withdraw the prop a cord or cable is hooked on to the loop 30 and is pulled to withdraw the piston member 2| awayfrom the valve which latter is thereby freed to unseat under the pressure of the actuating fluid which can thus flow from below the ram I through the tube I9 and passages I! and 4'] back into the ram I. The relief valve is therefore used also as an unloading valve. It will be appreciated that when withdrawal is required there will be a considerable roof weight acting on the prop so that the forces acting in opposition on the relief valve will more or less balance, with the result that the pull necessary to bring about unseating of the relief valve will be'very slight. When the prop has contracted sufficiently, continued pull on the cord or cable will cause the prop-to topple over about its base so that the prop can then be dragged endwise towards the operator who is standing at a safe distance away. The air valve 3| is provided to permit air to pass into the upper end of the ram I when a considerable extension of the prop is being brought about by operation of the pump. There would otherwise be created in the ham a partial vacuum which would interfere with the proper operation of the pump. Also when the prop contracts a considerable amount the air in the upper part of the ram is correspondingly compressed and some of it may escape by forcing its way through the breather slit 34 in the valve.

I claim:

1. In a telescoping hydraulic jack for use as a pit prop in mines, jack casing formed of two relatively collapsible and extensible members defining an expansible-volume work chamber therebetween, a storage chamber in one of the members, said storage chamber containing and the work chamber being filled with a motive fluid during operation as a prop, admission duct and valve means between the chambers permitting flow of such fluid from the storage to the work chamber, a return duct between the chambers, means to apply pressure to the fluid to move the fluid from the storage to the Work chamber for extending said members, a prop-handling member adapted to receive a pull for dragging the prop, a reciprocable, lost-motion connecting means interconnecting said prop-handling member and said casing, holding means normally operable to hold said prop-handling member in a given relationship to said casing and yielda-ble by a pull on said prop-handling member to enable the latter and said lost-motion connecting means to move relative to said casing from said given relationship into positive pulling engagement with said casing with the lost motion of said connecting means taken up, and a valve normally closing such return duct and operatively connected to said prop-handling member for release from such closed position and collapse of the extensible members upon movement of the pulled prop-handling member following yielding of said holding means.

2. A hydraulic pit prop as inclaim 1, wherein the prop-handling member i formed as a handle loop, and the lost-motion connecting means comprises a pivot pin for said handle loop, and a slot in the casing receiving and guiding said pivot pin for displacement transversely of its pivot axis.

3. A hydraulic pit prop as in claim 1, including a bolt interconnecting the valve and the prophandling member and guided for movement from valve closed position, wherein the prop-handling member is in the given reltionship, to valve-open position, wherein the prop-handling memberhas moved through the lost-motion connecting means into positive pulling engagement with the casing, and including further a spring reacting between the'casing and the valve to close the latter and acting through said bolt to return the prop-han dling member to such given relationship, said spring constituting the holding means.

4. In a telescoping hydraulic jack for use as a pit prop in mines, a jack casing formed of two relatively collapsible and extensible members defining an expansible-volume work chamber therebetween, a storage chamber in one of the members, said storage chamber containing and the work chamber being filled with a motive fluid during operation as a prop, admission duct and valve means between the chambers permitting flow of such fluid from the storage to the work chamber, a return duct between the chambers, means to apply pressure to the fluid to move thefiuid from the storage to the work chamber for extending said members, a valve located in and controlling communication through said return duct, holding means retaining said valve normally in closed position, whereby to maintain the prop extended in load-bearing condition, a prop handling member adapted to receive a pull for dragging the prop, said holding means being operatively connected to said prop handling member to retain the latter in a given relationship to said casing means, but being yieldable by a pull on said prophandling member, initially to enable opening of said valve and collapse of the extensible members, and a 1ostmotion connectin means interconnecting said prop-handling member and said casing means, to enable initial opening of the valve by a pull on the prop-handling member,;

and to bring said prop-handling member into positive pulling engagement with the casing means when the lost motion of said connecting means has been taken up by such pull.

5. A hydraulic pit prop as in claim 4, wherein the prop-handling member is located adjacent an end of the casing means, whereby continued pull thereon after opening of the valve and subsequent positive pulling engagement of said prop handling member, will enable the prop to be dragged away endwise by a pull initiated from a distant point.

6. A hydraulic pit prop as in claim 4, including a bolt interconnecting the valve and the prophandling member for positive movement of said member to its given relationshi upon movement of the valve to closed position, a spring urging the valve into closed position and constituting the holding means, a second lost-motion means interconnecting the bolt and one or the other of the prop-handling member and the valve, for opening of the valve in opposition to said spring for relief of duct pressure in excess of a predetermined value, independently of movement of said prop-handling member.

7. A hydraulic pit prop as in claim 4, including an elongated valve housing directed transversely of and secured rigidly to the casing adjacent its upper end, the return duct including said valve housing, and the valve being guided in and for opening and closing movement lengthwise of said housing, means including a bolt interconnecting the prop-handling member and the valve, through the housing, a spring constituting the holding means and reacting between the valve housing and the valve to hold the latter yieldably closed, and through said bolt urging the prop-handling member into its given relationship to the casing, said prop-handling member being arranged for operative movement from such given relationship by a pull in a direction generally transverse to the casing.

8. A hydraulic pit prop as in claim 7, wherein the bolt is fixedly connected to the prop-handling member, and including a second lost-motion means forming part of the interconnection between the prop-handling member and the valve, said second lost-motion means including a head on the bolt, and a shouldered guide on the valve engageable with the bolts head to urge thelatter and the prop-handling member into the latters given relationship upon closure of the valve, but permitting opening of the valve for relief, independently of movement of the prop-handling member from such given relationship.

9. A hydraulic pit prop as in claim 4, including an elongated valve housing directed transversely of and secured rigidly to the casing adjacent its upper end, the return duct including said valve housing, and the valve being guided in and for opening and closing movement lengthwise of said housing, means including a bolt interconnecting the prop-handling member and the valve and directing lengthwise of the valve housing, a spring constituting the holding means, disposed within the casing and urging the valve into closed position, and through said bolt urging the prop-handling member into its given relationship to the casing, and the prop-handling member being formed as a handle loop pivotally hung from said bolt, externally of the casing, for pulling engagement from a distant point to release the valve and to drag away the prop.

G. H. DOWTY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 151,670 Ojeda, June 2, 1874 1,133,270 Dale Mar. 30, 1915 1,598,426 Ditson Aug. 31, 1926 1,706,309 Miller Mar. 19, 1929 1,805,588 Manley May 19, 1931 2,284,2 8 Page May 26, 1942