Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to longwall jacks and
particularly to hydraulically operated longwall jacks which
release and yield at a preselected pressure while continuously
maintaining the preselected yield pressure as they yield.
The use o~ longwall jacks has been proposed in the
coal mining industry in the past as a replacement for cribbing
and the like. There have been a variety of problems with the
prior art longwall jacks. Many of them were expensive and
complicated in structure. Generally, they were heavy and
required a hydraulic oil pump for their installation. Moreover, ~;
thev had poor yield characteristics, would bend or deform rather
than yield and were difficult to recover and reuse.
We have developed a yieldable longwall jack which is
light in weight, very simple in structure, operates on water or
other fluid pressure, yields at a preselected pressure while
continuously maintaining said pressurè and which can be readily
recovered and reused.
The invention provides a longwall jack comprising an
elongate piston having a floor engaging base at one end, a
cylinder slidingl~ surrounding substantially the length of said
piston on the other end, a solid roof engaging head integrally
bonded on said cylinder opposite said base, said head including
a radially extending flange at the end remote from the piston,
said flange extending substantially beyond the periphery of the
cylinder, one-way inlet means in said head communicating with
the interior of the cylinder above the piston, first outlet
means in said head communicating with the interior of said
cylinder above the piston, pre-set pressure release means in
said outlet means releasing fluid from the cylinder each time
the pressure therein exceeds a selected pre-set pressure, a
second outlet means in said head spaced from said inlet means
and said first outlet means communicating with the interior of
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the cylinder above the piston, pressure release valve means in
said second outlet means and operator means pivoted on said head
engaging said pressure release valve means whereby a pull on
said operator means opens said pressure release valve means in
said second outlet means to release fluid from the cylinder and
permit it to slide over the piston, said flange on said head
extending substantially over said operator means.
The pressure release valve means is preferably a
spring loaded ball and a rod moves in a passage in said head
against the ball at one end and at the other end against a cam
actuator on a handle. Preferably, the one-way inlet means is
an Alemite type one-way valve. The base on said one end of the
piston is preferably slightly hemi-spherical. Preferably the
cylinder is pressurized with water or a water emulsion.
In the foregoing general statement of our invention~
we have set out certain preferred embodiments and practices of
our invention. Other objects, purposes and advantages of this
invention will be apparent from a consideration of the follow-
ing ~escription and the accompanying drawings in which:
Figure 1 is a vertical section through a longwall jack
according to our invention;
Figure 2 is a top plan view of the head of the jack
of Figure l;
Figure 3 is a section on the line III-III of Figure 2;
Figure 4 is a section on the line IV-IV of Figure 2;
and
Figure 5 is a fragmentary side elevational view of the
jack of Figure 1.
Referring to the drawings, we have illustrated an
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elongate piston 10 having a base 11 at one end. An outer
cylinder 12 surrounds piston 10 above base 11 and carries a
head 13 with cap 13a at the end opposite base 11. Base 11 is
preferably provided with a convex bottom, as shown. The end 14
of cylinder 12 opposite head 13 carries a wiper ring 15 and a
wiper ring 16, which slides on piston 10. An annular stop ring
17 is provided on the piston spaced from base 11 to limit the
relative movement of piston 10 and cylinder 12. The end lOa of
piston 10 opposite base 11 carries annular seal 18, back up
ring 19 and packing 20 which bear on the wall of cylinder 12
and seal the piston in the cylinder. The cylinder head 13 is
provided with an inlet passage 21 which communicates from the
side of head 13 to the interior of cylinder 12 above the piston
10. An Alemite (trademark) type inlet check valve fitting 22
is provided in the inlet passage to permit introduction of
hydraulic fluid from the outside inl:o cylinder 12 above piston
10. A first outlet passage 23 is provided in head 13, spaced
from and generally paralleling inlet passage 21, and
communicating from the interior of cylinder 12 above piston 10
to the outside. A pressure relief valve 24 is provided in this
first outlet passage and is pre-set to the pressure at which it
i5 desired to cause the jack to yield, e.g., 22.5 tons. A
second outlet passage 25 is provided in head 13 communicating
from the interior of cylinder 12 above piston 10 to the
exterior of the head through a check valve 26 in transverse
passage 26a and deflector 27. A manually operated valve 28 is
provided in passage 25 in the form of a spring loaded ball 29
in a seat 30 at the connection of passage 25 to passage 26a.
An elongate handle 31 is pivoted at one end 31a in trunnions 32
on head 13 and normally lies parallel to cylinder 12. The
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other end 31b o~ the handle has a cross rod 31c to be pulled by
hand or to receive a retrieving rope or cable Inot shown). The
one end 31a of handle 31 has a cam surface 34 which bears
against a pin 35 in passage 3~ aligned with ball 29. When
handle 31 is pulled outwardly on its pivot to a position
transverse to cylinder 12, cam surface 34 forces pin 35 to
press ball 29 in against spriny 29a and thus releases fluid
from the interior of cylinder 12. The head 13 is provided with
a radially extending flange 13b which extends radially beyond
the periphery of the cylinder and substantially over handle 31
and pin 35.
In operation the jack of this invention is placed in
position and extended and pressurized by introducing water
under pressure through Alemite (trademark) inlet check valve
fitting 22 so as to fill the area of the cylinder 12 between
head 13 and piston 10 with water and to cause relative movement
between cylinder 12 and piston 10, bringing cap 13a on head 13 ~ ~ -
in contact with the mine roof to be supported. Water or water
emulsion is added until the jack is pressurized to the desired
level. In the event that the pressure of the roof on the jack
exceeds the pre-selected relief pressure, e.g. 22.5 tons, the
jack will automatically release water or wa~er emulsion-through
first outlet passage 23 and pressure relief valve 24 to
maintain a continual resistance at the pre-selected relief
pressure and will not bend or deform or be destroyed as was the ~;
case with many jacks of the past.
In the event that it is desired to remove the jack
and retrieve it, cross rod 31c is pulled or a rope or cable is
attached around cross rod 31c in handle 31 and a workman by
pulling on the cable from a safe position raises handle 31 to a
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position transverse to cylinder 12, causing cam surface 34 to
force pin 35 against ball 29 pushing it away from its seat and
releasing water or water emulsion from the interior of cylinder
12 through passages 25 and 26a, check valve 26 and deflector
27. This causes cylinder 12 to collapse over 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 to the workman. ~ /:
In the foregoing specification we have set out
certain preferred practices and embodiments of our invention,
however, it will be understood that this invention may be
otherwise variously embodied within the scope of the following
claims.
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