US3046947A

US3046947A - Hydraulic props

Info

Publication number: US3046947A
Application number: US50795A
Authority: US
Inventors: Reynolds Reginald; Stammers Peter Haig
Original assignee: Acrow Engineers Ltd
Current assignee: Acrow Engineers Ltd
Priority date: 1959-08-21
Filing date: 1960-08-19
Publication date: 1962-07-31
Anticipated expiration: 1979-07-31
Also published as: GB962543A

Description

July 31, 1962 R. REYNOLDS ET AL HYDRAULIC PROFS Filed Aug. 19, 1960 3,046,947 HYDRAULIC PRPS Reginald Reynolds and Peter Haig Stammers, Salron Walden, England, assignors to Acrow (Engineers) Limited, London, England Filed Aug. 19, 1960, Ser. No. 50,795 Claims priority, application Great Britain Aug. 21, 1959 4 Claims. (Cl. 121-46) This invention relates to hydraulic props especially pit props of lthe type comprising a ram working in a cylinder which, on operation of a pump to cause oil or other Working iluid to be forced past a valve in the -ram head into a pressure chamber between the lower end of the ram and the closed end of the cylinder, is extended out from the cylinder. In order to retract such hydraulic props the iluid pressure in the pressure chamber has to be relieved and this is done by opening a release valve which is arranged normally to close a connection between the pressure chamber and a reservoir.

It is important that 'a hydraulic pit prop be completely under the miners control when it is being contracted for removal and re-use elsewhere. The rate at which this contraction occurs must be dependent on the root` conditions and it must be possible to arrest the contraction at any instance. Although it may appear from theoretical considerations that it is advantageous to contrive that the rate of contraction be varied automatically with variations in the load on the prop or when the prop is at a particular level, this is not attractive as a practical proposition. Among the reasons for this are that the prop is not suiiiciently under the control of the miner and that where as is to be expected, the load is Ibalanced or resisted by a spring, hunting between slow and rapid contraction is likely to occur.

A hydraulic prop in accordance with the invention incorporates a release valve comprising a main valve element which has a bleed passage of small size through it, the closure member of which bleed passage is also of relatively small size so that the force which has to be applied to it to unseat it against a given uid pressure is small, the main valve element `being of greater size so that the force which is to be supplied to unseat ift against the given uid pressure is relatively substantial, means being lprovided to open the main valve element and the bleed passage closure member in such a way that the closure member is unseated to open the bleed passage before the main valve element is unseated. As the force required -to perform the latter operation when the prop is under load is substantial, the operator 'encounters a large resistance to further movement of the opening means once the bleed has been opened and is thus given the indication, lwhich he needs, that the load is following up the contraction of the prop. If the roof is holding up, the resistance to further movement of the opening means is small and the miner knows that he can open the main valve element and cause the prop to collapse rapidly without danger.

The opening means preferably comprises a push rod or the equivalent which is caused to move down within the prop by a miner from outside the prop.

An example of an arrangement in accordance with the invention is shown in the acompanying drawing which is a section through the lower end vof a prop.

The prop comprises a cylinder in which is mounted for movement a ram 12 having a head 14. In the particular example `shown here, provision is made for low pressure pumping when the load is light and high pressure pumping when a pre-determined load is exceeded. The high pressure piston is shown at 16 and the low pressure piston at 17. The pistons are reciprocated by a piston rod tube 18 operable from outside the prop.

Y 3.046,@47 Patented July 31, 1962 In the head 14 of the ram, there is `a passage normally v closed by a release valve comprising a main valve element 20 having an opening 22 in its side. The member 20 has a tlange 23 which is kept seated by a spring 24 and any pressure to which the working fluid in the main pressure chamber 26 is subjected. When it is so seated, the opening 22 in the side of the member 20 is sealed.

so as to always present resistance to roof movement.

The head of the member 20 has a bleed hole 30 through it which is closed by a ball 32 subjected to the pressure of a spring 34 and the pressure in the chamber 26.

35 indicates a yield valve which allows uid to bleed from the pressure chamber 26 to a reservoir in the ram above the low pressure piston 17, if the pressure in the chamber 26 rises above a pre-determined maximum. In this way if the prop when set is subjected to very high rforces due to a falling roof it gives or contracts slightly If the prop were rigid there would be a danger of it snapping.

When the prop is to be contracted, the miner actuates push rods 38, 39 (by means not shown such las those forming the subject of our `co-pending Application Serial No. 50,794 tiled August 19, 1960) the llatter of which rods passes down into the cavity within the valve element 20. Lowering ot the push rod brings it into .contact with a pin 40 which has ats formed on its sides so as to provide apassage through bleed hole 30. The bottom of the pin 40 rests on the ball 32. A relatively :light pressure causes the ball to be unseated so that the working fluid bleeds slowly through the passage 30 around the pin 40 and the ram descends very slowly, say at a rate of 1A; inch per second.

When the bleed has thus Ibeen opened, the push rod,

meets the Vhead lof the main valve member 20. If the prop is under load, the pressure in the chamber 26 will be `high and as it acts on `a large area of the valve member, the force required to unseat that member will be substantial. T'ne existence of a substantial resistance to Yfurther movement of the push rod tells the miner that the prop is still under load and that either he must continue to contract the prop'at the low speed determined by the bleed or, if he wishes to contract the prop rapidly, he must do so from Ea distance by means, for example, of a Sylvester. It can, indeed, be contrived if desired that the means at the rniners disposal for actuating the push rod when close to the prop do not allow him to cause the main valve element to be unseated as long as the prop is under any susbtantial load say albove half a ton.

When the release valve is fully open fluid can iiow freely from the pressure chamber 26 up through the cylindrical portion of the main valve element 20 to the chamber 42 -above the ram head. From there it ows up inside the piston rod tube 18 and lout to the reservoir 44 above the low pressure piston 17 through orifices 46 and 4S.

lf when the prop has been contracted to some extent under the action of the bleedl the roof shows no tendency to fall, the load on the prop and the pressure in the chamber 26 will lfall ott and the miner Will then find little resistance to opening of the main valve and Will be able to cause the prop to contract rapidly with safety.

The construction of the release valve can be varied from that shown and is `of little importance in itself. The bleed and the main passage can, if desired be separate passages instead of one being located within the other. The important thing is that the closure member or valve Velement of the main passage should have a large surface acted upon by the pressure in the main pressure chamber and that it be operable only when the bleed has been opened.

In the arrangement shown the bleed is provided by the passage between the llats on the pin 40 and the sides of the bleed hole 30. This passage can be considered to have an area equal to that of a hole of 3%4 diameter.

` Y 3 The ball closing bleed hole Sil has a diameter of about 3/16" and the ilange of the main valve member a diameter of about 7a".

The rate at which the prop contracts depends, of course, on the load applied to it. With a l@ inch diameter bleed, a load of tons can belet down at a rate of one inch in 5 to 10 seconds.

It will be appreciated that insteadf the .bleed` passage being provided by the space btween the flats on pin 40 and the sides of hole 39, channels or grooves could be formed in the sides of the pin.

t The prop in accordance with the invention has the advantage over props in which the full opening of the release valve is governed by the load and is effected automatically in that there is little risk of its ever having to be abandoned Vbecause of a falling roof. It will be lappreciated that if the valve can be fully opened only when the prop is under substantially no load, there is no way of contracting the prop rapidly while it is under load and its removal can be effected only by brute `force while it is in the V extended condition and is supporting the roof; Whereas in a prop in accordance with the invention the miner will normally be able to open the main closure member 20l by extending a comparatively strong force on the opening device. He will of course realise that there is a following load and thus be able t0 tak Y appropriate precautions.

We claim:

l. A hydraulic prop comprising a cylinder, a ram slidvable in the cylinder, a pressure chamber in the cylinder below the ram head,a release valve closing a passage through the ram head connecting the pressure chamber, said release valve comprising a main valve element having a bleed passage through it and a closure member arranged normally to close said bleed passage, the main valve element being of greater size than said closure member so that the force which is to be applied to unseat it against a given fluid pressure in the pressure chamber is substantially greater than that needed to unseat said closure member, and a push rod extending down within the ram and being arranged to act irstly on said closure member to open said bleed passage and thereafter on said main valve element to open the passage connecting the pressure chamber and the reservoir.

2. A hydraulic prop as claimed in cla-im 1 in which said main valve element has a cylindrical portion which is a sliding tit in the passage passing through the lram head, said cylindrical portion being open at one end and closed at its other end by Va flange, said flange being arranged to seat on said ram head to close said passage, the bleed passage passing through the flange and connecting the pressure chamber and the interior of said cylindrical portion of the main valve element.

3. A hydraulic prop as claimed in claim 2 in which said cylindrical portion has an oritlcethrough its Ywall to allow hydraulic fluid to flow past said cylindrical portion through the ram head from the pressure chamber to the reservoir when the main valve element is opened.

4. A hydraulic prop comprising a cylinder, a ram slidable in the cylinder, a pressure chamber in the cylinder below the ram head, a release valve closing a passage through the ram head connecting/the pressure chamber and the reservoir, sa-id release valve comprising a main valve element having a bleed passage through it, said passage being normally closed by a ball, the main valve n,

element being of greater size than said =ball so that the force which is to be applied to unseat it against a given iluid pressure in the pressure cham-ber Vis substantially greater than that needed to unseat said closure member,

and a push rod extending down within the ram and having a pin portion at its lower end, said pin passing through a portion of said bleed passage to act on said ball to open the bleed passage, the push rod then acting on the main valve element to open the passage connecting y the pressure chamber and the reservoir.

Stelzer July 2, 17957