GB2069048A - Longwall jacks - Google Patents

Abstract

A longwall jack for use in coal mining comprises a piston 10 slidable in a cylinder 12. A cylinder head 13 contains a one-way inlet (not shown), a first outlet containing a pre-set pressure relief valve (not shown) and a second outlet 25. There is a pressure release valve 28 in the second outlet 25 operable by a handle 31 pivotted in trunnions 32 and having a cam surface 34 bearing on a pin 35 aligned with a spring loaded ball 29 of the release valve 28. The pre-set pressure relief valve keeps the pressure in the jack below a certain maximum, while the release valve 28 can be operated by pulling a cable connected to an end 31b of the handle 31. <IMAGE>

Description

SPECIFICATION Longwall jacks The invention relates to hydraulically operated longwall jacks suitable for use in coal mining which jacks release and yield at a preselected relief pressure while continuously maintaining the preselected pressure as they yield.

The invention provides a longwall jack comprising a piston having a base at one end, a cylinder slidingly surrounding the piston at the other end, a head on the cylinder opposite the base, a one-way inlet in the head communicating with the interior of the cylinder above the piston, a first outlet in the head communicating with the interior of the cylinder above the piston, a pre-set pressure relief valve in the first outlet for releasing fluid from the cylinder each time the pressure therein exceeds the pre-set pressure, a second outlet in the head communicating with the interior of the cylinder above the piston, a pressure release valve in the second outlet and a handle on the cylinder engaging the pressure release valve whereby a pull on the handle opens the pressure release valve and releases fluid from the cylinder and to permit it to slide over the piston.

Such a longwall jack may be made light in weight, and simple in structure, can operate on water or water emulsion or other hydraulic fluid, and can readily be recovered and reused.

The handle is preferably elongate and generally parallel to the cylinder axis, pivoted at one end to the head, and having an opening in the other end to receive a cable. The handle is preferably operable to open the valve means when pivoted away from the cylinder axis. The valve means is preferably a spring loaded ball, and the handle preferably operates the valve through a rod moving in a passage in the head at one end against the ball and at the other end against a cam actuator on one end of the handle. Preferably, the one-way inlet comprises an Alemite (Registered Trade Mark) type one-way valve. The base of the piston is preferably slightly hemi-spherical.

Drawings Figure 1 is a vertical section through a longwall jack according to the invention; Figure 2 is a top plan view of the head of the jack of Figure 1; Figure 3 is a section on the line Ill-Ill of Figure 2; Figure 4 is a section on the line IV--IV of Figure 2; and Figure 5 is a fragmentary side elevation of the jack of Figure 1.

With particular reference to Figure 1, an elongate piston 10 has a base 11 at one end. An outer cylinder 12 surrounds the piston 10 above the base 11 and carries a head 1 3 at the opposite end. The end 14 of cylinder 12 opposite head 13 carries a cover 1 5 with a wiper ring 1 6 which slides on the piston 10. An annular stop ring 1 7 is provided on the piston 10 spaced from base 11 to limit relative movement between the piston 10 and cylinder 1 2. The end of the piston 10 opposite the base 11 carries an annular seal 18, a back up ring 1 9 and packing 20 which bear on the wall of the cylinder 12 and seal the piston in the cylinder.

The cylinder head 1 3 is provided with an inlet passage 21 which communicates from the side of the head 13 to the interior of cylinder 12 above the piston 10. An alemite-type check valve fitting 22 is provided in the inlet passage 21 to permit introduction of hydraulic fluid from the outside into the cylinder 12 above piston 10. A first outlet passage 23 is provided in the head 13, spaced from and generally parallel to the inlet passage 21, and from the interior of the cylinder 1 2 above ths piston 10 to the outside. A pressure relief valve 2zi is provided in the first outlet passage 23, and is pre-set to the relief pressure at which it is desired to cause the jack to yield, e.g., 22.5 tons.A second outlet passage 25 is provided in the head 13 from the interior of the cylinder 12 above the piston 10 through a check valve 26 in a transverse passage 26a and past a deflector 27 to the outside.

A manually operated valve 28 is provided in the second outlet passage 25 in the form of a ball 29 loaded by a spring 29a against a seat 30 at a connection of the passage 25 to the passage 26a.

An elongate handle 31 is pivoted at one end 31 a in trunnions 32 on the head 13, and is normally parallel to the cylinder 12. The other end 31 b of the handle 31 has a cross rod 31 c to be pulled by hand or to receive a retrieving rope or cable (not shown). The one end 31 a of handle 31 has a cam surface 34 which bears against a pin 35 in a passage 36 aligned with the ball 29. When the handle 31 is pulled outwardly on its pivot to a position inclined or normal to the cylinder 12, the cam surface 34 forces the pin 35 to press the ball 29 in against the spring 29a and thus release fluid from the interior of the cylinder 12.

In operation, the jack is placed in position and extended and pressurized by introducing water under pressure through the Alemite (Registered Trade Mark) fitting 22 so as to fill the area of the cylinder 12 between the head 1 3 and piston 10 with water and to cause relative movement between cylinder 1 2 and piston 10, bringing a cap on the head 1 3 into contact with the mine roof to be supported. Water is added until the jack is pressurized to the desired level. Whenever the pressure of the roof on the jack exceeds the preselected relief pressure, the jack automatically releases water through the first outlet passage 23 and the pressure relief valve 24 to maintain a continual resistance at the relief pressure, and will not bend or deform or be destroyed.

If it is desired to remove and/or retrieve the jack, the cross rod 31 c is pulled or a rope or cable is attached around the cross rod 31 c in the handle 31 and a workman by pulling on the cable from a safe position raises the handle 31 to a position inclined or normal to the cylinder 12, causing the cam surface 34 to force the pin 35 against the ball 29, push it away from its seat and release water from the interior of the cylinder 12 through the passages 25 and 26a, and the check valve 26, and past the deflector 27. This causes the cylinder 12 to collapse over the piston 10 and move away from the supported roof. Continued pulling on the rope or cable will cause the jack to fall over on its side and be pulled toward the workman.

Claims (1)

1. A longwall jack comprising a piston having a base at one end, a cylinder slidingly surrounding the piston at the other end, a head on the cylinder opposite the base, a one-way inlet in the head communicating with the interior of the cylinder above the piston, a first outlet in the head communicating with the interior of the cylinder above the piston, a pre-set pressure relief valve in the first outlet for releasing fluid from the cylinder each time the pressure therein exceeds the pre-set pressure, a second outlet in the head communicating with the interior of the cylinder above the piston, a pressure release valve in the second outlet and a handle on the cylinder engaging the pressure release valve whereby a pull on the handle opens the pressure release valve and releases fluid from the cylinder and to permit it to slide over the piston.

2. A longwall jack according to claim 1 in which the handle is elongate and pivoted at one end to the head, and having an opening in the other end to receive a cable.

3. A longwall jack according to claim 2 in which the handle has a cam engageable with cam follower in the head engaging the pressure release valve, the cam surface acting on the cam follower to open the valve when the handle is pivoted from its normal position to a position inclined or normal to the cylinder axis.

4. A longwall jack according to any preceding claim in which the piston base has a hemispherical bottom surface.

4. A longwall jack according to any preceding claim in which the one-way inlet comprises an Alemite (Registered Trade Mark) type one-way valve.

6. A longwall jack as claimed in any preceding claim in which the pre-set pressure release valve is a spring loaded relief valve.

7. A longwall jack according to any preceding claim in which the head has a fluid diverter on the second outlet for diverting fluid discharged generally parallel to the axis of the cylinder and towards the base of the piston.

8. A longwall jack as herein described with reference to the drawings.