U.S. patent number 3,821,880 [Application Number 05/167,832] was granted by the patent office on 1974-07-02 for hydraulic control systems and devices therefor.
This patent grant is currently assigned to Gewerkschaft Eisenhutte Westfalia. Invention is credited to Volker Behrens, Werner Grommas, Alfred Marquart, Walter Weirich.
United States Patent |
3,821,880 |
Weirich , et al. |
July 2, 1974 |
HYDRAULIC CONTROL SYSTEMS AND DEVICES THEREFOR
Abstract
A hydraulic control system for use with mineral mining roof
support installations the system having a control device which can
be manually set into various positions to effect certain operations
in the components of the installation, such as retraction and
extension of roof engaging props, and shifting of support units and
a conveyor. The system can perform a certain sequence of operations
entirely automatically and the system employs valve devices with
two servo pistons either of which is adapted to actuate the valve
device when exposed to pressure medium. One servo piston is used
when the installation is controlled manually and the other piston
is used when the installation is controlled automatically. The
automatic section of the system includes one or more timing
mechanisms and fluid flow regulators which initiate various parts
of the control sequence.
Inventors: |
Weirich; Walter (Dortmund,
DT), Grommas; Werner (Dortmund-Wickede,
DT), Behrens; Volker (Dortmund-Mengede,
DT), Marquart; Alfred (Altlunen, DT) |
Assignee: |
Gewerkschaft Eisenhutte
Westfalia (Wethmar bei Lunen, Westfalia, DT)
|
Family
ID: |
27182794 |
Appl.
No.: |
05/167,832 |
Filed: |
July 30, 1971 |
Foreign Application Priority Data
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Aug 4, 1970 [DT] |
|
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2038661 |
Aug 4, 1970 [DT] |
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2038663 |
Oct 10, 1970 [DT] |
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2049869 |
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Current U.S.
Class: |
405/302;
137/637.4 |
Current CPC
Class: |
E21D
23/0073 (20130101); E21D 23/26 (20130101); Y10T
137/87137 (20150401) |
Current International
Class: |
E21D
23/00 (20060101); E21D 23/26 (20060101); E21d
015/44 () |
Field of
Search: |
;61/45D
;137/625.12,625.13,625.15,637.4 ;191/453,461,17MP ;299/31,33 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Taylor; Dennis L.
Claims
We claim:
1. In a hydraulic control system including a source of pressure
medium, a combination of valve devices and pressure medium conduits
connected to consumer appliances and a manually operable control
device for selectively actuating the valve devices to feed pressure
medium to and from the applances to perform various operations, the
improvement therein comprising at least some of the valve devices
each having two servo-pistons and associated working chambers, the
servo-pistons being adapted to operate the valve devices when
pressure medium is conveyed to the associated working chambers,
means operably connecting one of the working chambers to said
control device and means operably connecting the other of the
working chambers to part of the system for automatically effecting
a sequence of operations on the appliances.
2. A system according to claim 1, wherein a plurality of said valve
devices are formed into a common constructional unit with the
control device.
3. A system according to claim 1, wherein the two servo-pistons of
said valve device are disposed co-axially of one another.
4. A system according to claim 1, wherein each valve device having
said two servo-pistons has two shut-off valves each with a closure
element engageable on a seating with the closure elements being in
engagement with a common plunger, the servo-pistons being adapted
to act upon one of the closure elements to open one valve and shut
the other valve.
5. A system according to claim 3, wherein the valve device has a
housing and the two servo-pistons are displaceably mounted in a
guide bush received in the housing, there being further provided
two shut-off valves each with a closure element engageable on a
seating with the closure elements being in engagement with a common
plunger, the servo-pistons being adapted to act upon one of the
closure elements to open one valve and shut the other valve, and
wherein the closure elements are each mounted in a sleeve
accomodated in the housing and the plunger extends through the
seatings of the valves.
6. A system according to claim 1, wherein the control device has a
setting position which initiates the automatic control
sequence.
7. In combination with a mine roof support installation having a
plurality of roof support assemblies, each having hydraulically
operated props, and at least one shifting ram for moving the
assemblies in relation to one another, a hydraulic control system
comprising: a source of pressure medium, valve devices and pressure
medium conduits connected to the props and the ram, and a manually
operable control device for selectively actuating the valve device
to actuate selected valve devices to cause pressure medium to be
fed to and from the props and the ram to perform various operating
steps, wherein at least some of the valve devices each have two
servo-pistons and associated working chambers, the servo-pistons
being adapted to operate the valve device when pressure medium is
conveyed to the associated working chambers, means operably
connecting one of the working chambers to the control device and
means operably connecting the other of the working chambers to part
of the system for automatically effecting a sequence of operations
on the props and the ram.
8. In a hydraulic control system including a source of pressure
medium, a combination of valve devices and pressure medium conduits
connected to consumer appliances and a manually operable control
device for selectively actuating the valve devices to feed pressure
medium to and from the appliances to perform various operations,
the improvement therein comprising: the control device having a
rotatable member and a fixed plate provided with a plurality of
bores, and a further bore in the plate, the rotatable member having
at least one bore therein which can be bought into sealed register
with each of the plurality of bores in the plate as the member is
rotated, the rotatable member also having a further bore which
communicates with the further bore in the plate, there being
further provided a shut-off valve operably disposed to open and
close communication between the further bore in the member and the
at least one bore in the member, at least some of the plurality of
bores in the plate being in communication through suitable
hydraulic lines with associated servo-control working chambers so
that the manual operation of the control device causes an
associated valve member to be actuated, each valve member further
including a second servo-control working chamber, and means being
provided to operably connect the second working chamber to part of
the system for automatically effecting a sequence of operations on
the appliances.
9. A system according to claim 8, wherein the control device has a
lever for effecting rotation of the member and for effecting
actuation of said valve.
10. A system according to claim 9, wherein the rotatable member is
partly received in a housing attached to said plate and the
rotatable member has an extension part which extends through an
aperture in the housing and carries said lever.
11. A system according to claim 8, wherein the shut-off valve is in
the form of a closure element biased by a spring against a seating,
accomodated in an axial bore of the rotatable member which
constitutes said further bore, said at least one bore is provided
in a disc part of the member and there is provided a displaceable
plunger for moving the closure element off the seating.
12. A system according to claim 8, wherein the plurality of bores
in the plate lie on a common pitch circle with its centre at the
rotational axis of the rotatable member, the further bore in the
plate is aligned with the rotational axis of the member, and the
plate has another bore disposed between said pitch circle and the
further bore end communicating with an annular gap disposed between
the rotatable member and an inner planar face of the plate.
13. A system according to claim 12, wherein said at least one bore
in the rotatable member contains a sealed sleeve adapted to be
urged into sealing relationship with said planar face of the plate
by means of the pressure of the pressure medium conveyed
therethrough.
14. A system according to claim 8, wherein there is provided detent
means for causing the rotatable member to be indexed into various
angular positions as the member rotates so that each of the
plurality of bores in the plate is successively brought into
communication with said at least one bore in the rotatable
member.
15. A system according to claim 8, wherein the rotatable member is
received in a housing attached to the plate, there being provided
roller bearings located between the housing and the member.
16. In combination with a mine roof support installation having a
plurality of roof support assemblies, each with hydraulically
operated props, and at least one shifting ram for moving the
assemblies in relation to one another, a hydraulic control system
comprising: a source of pressure medium, valve devices, at least
some of the valve devices each having two servo-pistons and
associated working chambers, the pistons being adapted to operate
the valve devices when pressure medium is conveyed to either
working chamber, and pressure medium conduits connected to the
props and the ram, a manually operable control device being
settable to various operating positions to actuate selected valve
devices to cause pressure medium to be fed to and from the props
and the ram to effect various operating cycles including extension
and retraction of certain of the props and shifting of certain of
the assemblies, means operably connecting one of the working
chambers of each valve device with the control device and means
operably connecting the other of the working chambers of each valve
device to part of the system for automatically effecting a sequence
of operations, wherein the control device includes a setting which
when adopted causes the retraction of the props of one assembly and
the shifting of the assembly effected by the automatic ram to be
initiated simultaneously.
17. An installation according to claim 16, wherein the control
device comprises: a rotatable member and a fixed plate provided
with a plurality of bores, and a further bore in the plate, the
rotatable member having at least one bore therein which can be
brought into sealed register with each of the plurality of bores in
the plate as the member is rotated, the rotatable member also
having a further bore which communicates with the further bore in
the plate, there being further provided a shut-off valve operably
disposed to open and close communication between the further bore
in the member and the at least one bore in the member, at least
some of the plurality of bores in the plate being in communication
through suitable hydraulic lines with associated servo-control
working chambers so that the manual operation of the control device
causes an associated valve member to be actuated, each valve member
further including a second servo-control working chamber, and means
being provided to operably connect the second working chamber to
part of the system for automatically effecting a sequence of
operations on the appliances.
18. An installation according to claim 16, wherein the control
device has settings whereat some of the props of one of the support
assemblies are extended and retracted independently of the
remaining props of the assembly.
19. An installation according to claim 16, wherein the control
device has a setting whereat a sequence of operations composed of
the retraction of the props of one of the assemblies, the shifting
of said one assembly and the subsequent extension of the props is
effected automatically.
Description
BACKGROUND TO THE INVENTION
The present invention relates to a hydraulic control system and
components therefor and is particularly concerned with a control
system for use with a mine roof support installation.
With such an installation it is desirable to employ a control
system which will enable the props of the individual support frames
or assemblies to be retracted or extended and the frames to be
shifted at the required time.
Hydraulic control systems are known in which the control of
operations is effected remote from the installation or else in
situ. In the latter case, each support frame is associated with a
manually operable control unit which effects control of the
adjacent support frame. In this way the operator can to some extent
be safeguarded by the frame bearing the control unit whilst the
neighbouring unit is being shifted. The remote control system
usually employs a manually operable appliance which is operated
whenever a particular operation in the installation is to be
performed. Other remote control systems employ certain devices
which effect some change in an operating cycle automatically. It is
well known, for example, that when an individual frame of the
installation is to be shifted, the props of the frame are first
retracted, the frame is then bodily shifted and finally the props
are extended to set against the roof. It is, under certain
circumstances, possible to shift the frame while maintaining the
props under load, either full or partial load, but this is only
possible if the roof of the mine working is substantially smooth
and flat.
In general, where mine conditions are liable to change the known
control systems are inflexible and there is a need for an improved
system which is more versatile and enables the operator to effect a
variety of different operations not possible with known systems in
order to cope with different conditions. Where conditions permit,
it is desirable for the system to perform an entirely automatic
control sequence.
A general object of this invention is to provide an improved
control system and components therefor.
SUMMARY OF THE INVENTION
In its broadest aspect the invention provides a hydraulic control
system comprising a plurality of valve devices, a plurality of
pressure medium conduits interconnecting said valve devices and a
number of consumer appliances, and a single manually operable
control device for hydraulically activating selected valve devices
to cause pressure medium to be fed to and from said appliances to
perform various operations.
In another aspect the invention provides a hydraulic control system
comprised of a source of pressure medium, a combination of valve
devices and pressure medium conduits connected to consumer
appliances, e.g., the props and shifting ram of a mine roof support
system, and a manually operable control device for selectively
activating the valve devices to feed pressure medium to and from
the appliances. At least one of the valve devices has two servo
pistons and associated working chambers, the pistons being adatped
to operate the valve devices in the same manner when the pressure
medium is conveyed to the associated working chamber, one of the
working chambers being operably connected to said control device
and the other of the working chambers being operably connected to
part of the system for automatically effecting a sequence of
operations on said appliances.
In another aspect the invention provides in combination with a mine
roof support installation composed of a plurality of roof support
assemblies, and each with hydraulically operated props, and at
least one shifting ram for moving the assemblies in relation to one
another a hydraulic control system; said system comprising a source
of pressure medium, valve devices, and pressure medium conduits
connected to said props and said ram, and a manually operable
control device settable to various operating positions to actuate
selected valve devices to cause pressure medium to be fed to and
from the props and the ram to effect various operating cycles
including extension and retraction of certain of the props and
shifting of certain of the assemblies, wherein the control device
includes a setting which when adopted causes the retraction of the
props of one assembly and the shifting of the assembly effected by
the associated ram to be initiated simultaneously.
The aforesaid valve device with two pistons may comprise a housing,
a first valve composed of a closure element engageable on a seating
disposed in said housing, a second valve composed of a closure
element engageable on a seating disposed in said housing, a plunger
disposed in contacting relationship with the closure elements of
said first and second valves, a spring acting to urge the closure
element of the first valve onto its seating and acting through the
plunger to urge the closure element of the second valve off its
seating, a first servo piston and a first working chamber therefor
disposed adjacent the second valve, and a second servo piston and a
second working chamber therefor disposed adjacent the working
chamber of the first servo piston and inlets to the working
chambers of the first and second servo pistons whereby admission of
pressure fluid into either of said chambers through the associated
inlet displaces one or both servo pistons to urge the closure
element of the second valve onto its seating and, through the
plunger, the closure element of the first valve off its
seating.
In a preferred construction the control device comprises a
hydraulic control device comprising a plate having a first bore and
a plurality of additional bores the addition of bores being
arranged on a common pitch circle, a housing attached to said
plate, a rotatable member disposed within the housing and scaled in
relation thereto, the rotatable member having at least one bore
which can be brought into registration with each of said additional
bores in the plate as the member is rotated, a shut-off valve
operably disposed to open or close communication between said first
bore in the plate and said at least one bore in the rotatable
member, and means for actuating said shut-off valve.
By utilizing control valve devices with two servo pistons, one for
manual control and one for automatic control, the number of valve
devices required for the overall system is reduced.
Among the special operations that the system can perform on a mine
roof support installation a special mention may be made of an
operation whereby the retraction of the props of a support frame
and the shifting of the frame are performed simultaneously thus
speeding up the shifting process. Obviously, when conditions
permit, the system can be switched over to entirely automatic
control. However, in difficult conditions manual control can be
effected and one of the facilities of the system enables the front
and rear props of a frame to be extended or retracted
independently. Thus, the props can be readily aligned.
Where the roof conditions are difficult, an operator can effect the
shifting operation manually in the various oprating stages known
per se, i.e., retraction of the props, shifting of the frame and
re-setting of the props.
BRIEF DESCRIPTION OF DRAWINGS
The invention may be understood more readily and various other
features of the invention may become more apparent from
consideration of the following descriptions in conjunction with the
accompanying drawings, wherein:
FIG. 1 is a schematic diagram of a hydraulic control system
utilized with a mine roof support installation;
FIG. 2 is a schematic diagram of a further form of hydraulic
control system also utilized with a mine roof support
installation;
FIG. 3 depicts a modified part of a hydraulic control system
arrangement
FIG. 4 is a sectional view of one form of control device which can
be used in the control arrangements;
FIG. 5 is a side view of a unit composed of the control device and
various valve devices associated therewith;
FIG. 6 is a plan view of the unit shown in FIG. 5;
FIG. 7 is a sectional view of a servo control valve device which
can be used in the control system;
FIG. 8 is a side view of the valve device shown in FIG. 7;
FIG. 9 is a schematic diagram of another hydraulic control, system
utilized with a mine roof support installation;
FIG. 10 is a sectional view of another control device which can be
used in the control arrangements; and
FIG. 11 is a plan view of the device shown in FIG. 10.
DESCRIPTION OF PREFERRED EMBODIMENTS
Before considering the hydraulic control systems or arrangements of
the invention, it may be more informative to consider the
construction of a control device usable in such arrangements.
Referring initially to FIG. 4 there is shown a control device
generally designated S. The device S has a plate 10 provided with a
number of axially extending bores serving to establish connection
with the device S.
In this construction there are twelve such bores Z.sub.1 to to
Z.sub.12 arranged to lie on a common pitch circle described from
the center of the plate 10. The plate 10 has an inner planar
surface 11 and a recessed portion 12 separated from the surface 11
by an annular shoulder 13. A pot-like housing 14 is detachably
secured to the plate 10 as by screw-threaded engagement. A
rotatable member 15 is located partly within the housing 14. This
member 15 has a disc-like portion which is sealed in relation to
the internal surface of the housing 14 by means of a sealing ring
16 and an axial portion 22 which extends through a central hole in
the housing 14. The portion 22 is sealed in relation to the inner
surface of the hole in the housing 14 by means of sealing rings 23
and 24. The member 15 also has a spigot portion 17 which is
pivotably received in a bore 18 disposed centrally of the plate 10.
The portion 17 is sealed in relation to the internal surface of the
bore 18 by means of a sealing ring 19. The spigot portion 17
centralizes the member 15 in relation to the plate 10 and has a
longitudinal bore which establishes connection with a main pressure
conduit denoted P so that inlet pressure fluid for the device is
fed into the centre of the spigot portion 17. The outlet of fluid
from the device passes through a further axial bore 20 in the plate
10. The bore 20 is disposed inwardly of the bores Z.sub.1 to
Z.sub.12 in relation to the axis of the plate 10 and communicates
with an annular space 21 formed between the face 11 of the plate 10
and the inner-end face of one disc portion of the member 15.
The portion 22 of the member 15 has an internal bore 25 with
stepped-parts of successively smaller diameter containing a
plunger-operated non-return valve 26. The valve 26 has a closure
element 27 in the form of a ball which is urged against a seating
29 by means of a spring 28 located in the spigot portion 17. The
seating 29 is located by a shoulder of a recessed part of the main
bore 25. A sleeve 30 abuts the seating 29 and the sleeve 30 is
provided with a number of radial gaps 44 providing communication
between the interior and the exterior of the sleeve 30. The sleeve
30 and the seating 29 are retained by a hollow locking part 31
which is in screw-threaded engagement with part of the bore 25. A
plunger 32 is guided for longitudinal movement within the part 31
and the plunger 32 has an end portion 33 engageable with the
element 27. Sealing rings are disposed between the part 31 and the
bore 25, the plunger 32 and the part 31 and the seating 29 and the
bore 25. A lever 34 eccentrically mounted on the end piece 35 of
the portion 22 serves to effect displacement of the plunger 32 to
lift the element 27 off the seating 29 and open the valve 26.
The housing 14 is provided with an annular recess 36 which is
disposed externally of the pitch circle of the bores Z.sub.1 -
Z.sub.12 relative to the central axis of the device S. The recess
36 accomodates a roller beearing 37 which supports the member 15
for rotation about the central axis of the device S. The disc-like
portion of the member 15 contains a further bore 38 which
accomodates a ball 40 urged to the left of the drawing by means of
a spring 39. The housing 14 has a complementary surface formed wth
a series of depressions 41 arranged on a pitch circle to form a
detent means with the ball 40 such that the ball 40 can locate in
any one of these depressions 41 to bring the member 15 into various
operating positions.
The disc portion of the member 15 is further provided with a bore
42 facing the surface 11 of the plate 10. The bore 42 receives a
displaceable piston membr 45 which is urged by a spring 46 against
the surface 11. A sealing ring is provided between the member 45
and the bore 42 and a resilient packing member 47 is disposed
between the outer end of the bore 42 and the face 11. The member 47
serves to seal the interior of the member 45 in relation to the gap
21. The inner end of the member 45 forms a piston surface and when
pressure fluid is conveyed through the member 45, the pressure of
the fluid acts on the piston surface to urge the member 45 towards
the face 11 to assist the sealing action of the member 47. The
interior of the member 45 is disposed radially outwardly from the
centre of the device S by a distance corresponding to the radius of
the pitch circle of the bores Z.sub.1 - Z.sub.12 so that as the
member 15 is rotated the interior of the member 45 can be brought
into sealed communication with each of the bores Z.sub.1 - Z.sub.12
in turn. The interior of the member 45 in turn radially of the disc
portion and the passage 43 leads to a space disposed between the
sleeve 30 and the bore 25. This space in turn communicates with the
interior of the sleeve 30 and hence with the valve 36 via the gaps
44 in the sleeve 30. Instead of a single bore 42 with the member 45
communicating with a single passage 43 a number of bores 42, and
accomodating a member 45 adjoining the passage 43 communicating
with the vale 26, can be provided.
As will become more apparent hereinafter, the bores Z.sub.1 -
Z.sub.12 can be connected to various components in a hydraulic
system or arrangement and would normally be operably utilized in
pairs. In FIG. 4, the bore Z.sub.1 is shown to be in communication
with the interior of the sleeve 30 but the valve 26 blocks
communication between the interior of the sleeve 30 and the entry
bore 18. By actuating the lever 34, the element 27 can be moved off
the seating 29 to establish communication between the bores
Z.sub.1, 18. Rotation of the member 15 can bring any of the bores
Z.sub.1 - Z.sub.12 into communication with the bore 18 and this is
preferably done when the valve 26 is closed so that there is no
appreciable friction between the packing member 47 and the face 11.
The return path of pressure fluid from some appliance to which
fluid is transmitted from one of the bores Z.sub.1 - Z.sub.12
selected by the member 15 is via another of the bores Z.sub.1 -
Z.sub.12 and through the space 21 to the bore 20. The balls 40 and
the associated depressions 41 effectively locate the member 15 in
various positions corresponding to selection of each of the bores
Z.sub.1 - Z.sub.12.
FIGS. 10 and 11 depict an alternative control device S made in
accordance with the invention. As shown the device S is composed of
a base plate 901 to which is attached a pot-like housing 903. The
roller bearing and ball locating catch as described in connection
with FIG. 4 are utilized to index the rotation of the member 902
relative to the housing 903. The member 902 has a disc portion
which is provided with two radial passages 904,904.sup.1 closed at
the outer periphery of the disc portion by means of plugs. The
passages 904,904.sup.1 communicate with axial bores 905,905.sup.1,
respectively, which extend to the annular surface 906 of the disc
portion. As shown in FIG. 10, the bores 905,905.sup.1 are disposed
at different distances from the axis of the member 902. Each bore
905,905.sup.1 accomodates a sleeve 907 which is urged outwardly
from the bore 905,905.sup.1 by means of a spring 908. The periphery
of each sleeve 907 is formed with a seal 909 which seals the sleeve
907 in relation to the interior of the bore 905,905.sup.1. In
addition, each sleeve 907 has at its outer end a further seal 910
which engages the inner surface 911 of the plate 901. The sleeves
907 are so constructed that the pressure of fluid therein tends to
increase the sealing action of the seals 910. Between the disc
portion of the member 902 and the surface 911 of the plate 901
there is defined a chamber 921 which communicates with a bore 922
provided in the plate 901. The bore 922 would normally be connected
to pressure fluid return conduit.
The bores 904,904.sup.1 communicate via a chamber 912, with the
interior of the member 902 which in turn can communicate with a
bore 913 provided at the centre of the plate 901. This bore 913 is
intended to connect to a pressure medium conduit. The interior of
the member 902 is provided with a non-return valve 914 with a
closure element in the form of a ball engageable on a seating. A
spring 923 biases the closure element onto the seating to close the
valve 914 to thereby block the space 912 from the bore 913. A
plunger 915 guided for axial displacement within the member 902 can
lift the element off the seating against the force of the spring
923 to open the valve 914. When the valve 914 is open, pressure
medium can pass from the bore 913 through the valve 914 and the
space 912 to the passages 904,904.sup.1 and thence to the bores
905,905.sup.1.
As shown particularly in FIG. 11, the plate 901 is pierced with a
number of bores 916, in this example, six, disposed on a common
pitch circle described from the centre of the plate 901. The plate
901 is also pierced with a number of further bores 916.sup.1, in
this example, six, arranged on a common pitch circle described from
the centre of the plate 901 which has a radius less than that of
the circle on which the bores 916 lie. The pitch circles for the
bores 916,916.sup.1 are such that the bores 916 align with the bore
905 and the bores 916.sup.1 with the bore 905.sup.1 as the member
902 rotates. As shown in FIG. 11, each of the bores 916.sup.1 is
angularly disposed between two of the bores 916 relative to the
centre of the plate 901 and vice versa. Thus, as the member 902 is
rotated the bores 916 916.sup.1 are alternatively brought into
register with the bores 905,905.sup.1.
The member 902 can be rotated by means of a lever 917 and the
housing 903 may bear indicia representing the various operative
positions or settings of the member 902. In additon to effecting
rotation of the member 902, the lever 917 can be pivoted in the
direction of arrow 918. The lever 917 is formed with surfaces 919,
920 and by pivoting the lever 917 the surface 919 can engage the
plunger 915 to displace the latter and thereby open the valve 914.
If the lever 917 is released at this stage the spring 923 will
operate to close the valve 914 and urge the plunger 915 against the
surface 919 of the lever 917 to pivot the lever 917 in the reverse
direction to arrow 918. By displacing the lever 917 sufficiently
far in the direction of arrow 918 to cause the surface 920 to
engage the plunger 915, the valve 914 will remain open and the
spring 923 will not under these circumstances affect the position
of the lever 917.
Thus, rotation of the member 902 effected by the lever 917 is used
to select the bores 916,916.sup.1 into which pressure fluid is to
be fed and subsequent pivoting of the lever 917 opens the valve 914
to permit pressure fluid to enter the selected bore
916,916.sup.1.
Normally, the bores 916,916.sup.1 would be operated in pairs with
the bore of each pair of bores being connected to the pressure
conduit, via the bore 913 and the valve 914 and the other bore
being connected to the return conduit, via the chamber 921 and the
bore 922. However, the return path can be provided externally of
the device S.
Various examples of complete control systems will now be described
commencing with the arrangement depicted in FIG. 1.
A hydraulic control arrangement which may employ the device S
discussed above, will now be described with reference to FIG. 1.
The control arrangement is operably connected to a number of
displaceable mine roof supports, frames or assemblies. One such
assembly is depicted in the drawing as employing four hydraulically
actuated telescopic props 60,60A where the numerals 60A denote the
rear props and the numerals 60 denote the front props relative to
the mineral face. A hydraulically actuated shifting ram 62 is used
to move the support assembly and the ram 62 has a piston rod 61
connected to a conveyor (not shown).
The control device S previously described in connection with FIG. 4
or FIGS. 10 and 11, is represented in a schematic manner in FIG. 1
where I to VII denote various operating positions of the device S.
A main pressure feed conduit P and a return conduit R are installed
in the mine gallery and the device S for each assembly is connected
to the conduits P and R via corresponding branch conduits denoted
P.sup.1 and R.sup.1 respectively. In FIG. 1 the device S is
connected to two such branch conduits P.sup.1 R.sup.1 by way of the
bores 18,20 respectively (see FIG. 4 and FIG. 10 reference numerals
913,922). The props 60 of the support assembly have allocated
thereto a common double-acting servo-control valve device 63 with
servo-pistons 63.sup.1 63.sup.11 and similarly the props 60A have
allocated thereto a common double-acting servo-control valve device
63A with servo pistons 63.sup.1 A,63.sup.11 A. A preferred
construction for these valve devices and other similar
servo-control valve devices to be introduced later, will be
described hereinafter. The valve devices 63,63A control the
extension i.e., the setting of the props 60,60A. The servo-piston
63.sup.1 63.sup.11 of the valve device 63 effect the same
operations and are merely moved by different control pressures
derived when the arrangement is working under manual control or
automatic control. The valve devices 63,63A are connected to the
appropriate working chambers 60.sup.11 of the props 60,60A via
conduits 64,64A respectively, and the valve devices 63,63A are
connected to the conduits P and R via conduits 67,68 and 67A,68A
respectively. The props 60,60A also have allocated thereto a common
doube-acting servo-control valve device 69 with servo-pistons
69.sup.1,69.sup.11 which control the retraction, i.e., robbing of
the props 60,60A. The valve device 69 is connected to the
appropriate working chambers 60.sup.1 of the props 60,60A via
conduits 70. The valve device 69 is also connected to the conduits
P and R via conduits 71,72 respectively.
Further working valves 65,65A are associated with the valves 63,63A
and each valve 65,65A is connected between the main return conduit
R and the conduit 64,64A via a conduit 66,66A. Each of the valves
65,65A operate hydraulically and constitutes a pressure-relief
valve and a retraction facility.
Double-acting servo control valve devices 73,79 with servo-pistons
73.sup.1,73.sup.11 79.sup.1,79.sup.11 are operably associated with
the shifting ram 62. More particularly, the valve devices 73,79 are
connected to working chambers 62.sup.11 62.sup.1 of the ram
62.sup.1 respectively via conduits 74,82 and to the conduits P and
R via conduits 75,76 and 80,81 respectively. Similarly, to the
valve devices 63,63A the valve device 73 is associated with a
further working valve 77 which is connected between the conduits 74
and R via conduit 78. The valve 77 operates hydraulically to
relieve the chamber 62.sup.11 of the ram 62 and constitutes a
pressure relief valve which effectively controls the counter
pressure exerted on the conveyor by the plough guided thereon.
A servo-control valve device 85 has a single servo-piston 85.sup.1
which is operably connected to a regulator 83 via a conduit 84, and
the valve device 85 is controlled by the regulator 83 in accordance
with the quantity of fluid flowing in the conduit 84. The valve
device 85 is in turn connected to a reversing valve 86 and to a
control conduit ST. The valve 86 is connected to the conduits P and
R and the valve 86 has a single servo-piston 86.sup.1 connected via
a conduit 86 and a timing mechanism 88 to the conduit P. The timing
mechanism 88 may be composed of a retardation valve controlled by a
throttled pressure accumulator which provides a certain pressure to
operate the valve after a certain time interval. The control
conduit ST leads to the adjacent support assembly and includes a
valve 89.
The control device S is connected to six conduits 90-95 which are
connected to the various valves mentioned above and in this example
the device S can be brought into seven operating positions denoted
I to VII which are represented diagrammatically in FIG. 1.
The arrangement operates as follows:
Position III
With the device S in position III all the conduits 90 to 95 are
connected to the return conduit R and the props 60,60A of the
support assembly are extended and set against the roof of the mine
working. The valve 77 is closed and the chamber 62.sup.11 of the
ram 62 is blocked in respect of the conduit R so that the ram 62
rigidly holds the conveyor. The valves 64,65A prevent the props
60,60A from being overloaded. If overloading should occur, the
pressure in the chamber 60.sup.11 in question will cause the
appropriate valve 65,65A to open to allow the pressure fluid to
discharge into the conduit R.
Position II
With the device S in position II the conduit 92 is connected to the
main pressure conduit P so that the servo-piston 73.sup.1 of the
valve device 73 is exposed to pressure. This results in the conduit
74 being connected to the conduit P via the conduit 76 and the
chamber 62.sup.11 of the ram 62 is charged with pressure fluid. The
piston rod 61 of the ram 62 consequently extends to urge the
conveyor towards the mineral face.
Position IV
When the device S is put into position IV the conduits 94,91 are
connected to the main pressure conduit P. The valves 65,65A are
subjected to control pressure via the conduits 94 and consequently
the chambers 60.sup.11 of the props 60,60A are connected to the
return conduit R. The servo-piston 69.sup.1 of the valve device 69
is also subjected to control pressure via the conduit 91 and
consequently the chambers 60.sup.1 of the props 60,60A are
connected to the pressure conduit P via the conduits 70,71. The
props 60, 60A are thus retracted.
Position V
When the device S is put into position V the conduits 93,94 are
connected to the pressure conduit P. The valves 65,65A are
subjected to control pressure via the conduits 94 consequently and
the chambers 60.sup.11 of the props 60,60A are connected to the
return conduit R. The servo-piston 79.sup.1 of the valve device 79
is also subjected to pressure via the conduit 93 and the valve
device 79 operates to connect the chamber 62.sup.1 of the ram 62 to
the pressure conduit R. The props 60,60A are thus released from the
roof pressure and the entire assembly is moved up relative to the
conveyor by retraction of the ram 62.
Position I
When the device is set to position I the conduit 90 is connected to
the pressure conduit P. The servo-piston 63.sup.1 A of the valve
device 63A is thus subjected to pressure and the valve device 63A
operates to connect the chamber 60.sup.11 of the rear props 60A to
the pressure conduit P. The two rear props 60A therefore extend to
become set against the roof independently of the front props
60.
Position VI
When the device S is set to position VI the conduit 95 is connected
to the pressure conduit P. The servo-piston 63.sup.1 of the valve
device 63 is thus subjected to pressure and the valve device 63
operates to connect the chambers 60.sup.11 of the front props 60 to
the pressure conduit P. The two front props 60 therefore extend to
become set against the roof independently of the rear props
60A.
Position VII
When the device S is put into position VII the conduits 90,95 are
connected to the pressure conduit P and the servo-piston
63.sup.1,63.sup.1 A of the valve devices 63,63A are subjected to
pressure. The valve devices 63,63A operate to connect the chambers
60.sup.1 of all the props 60,60A with the pressure conduit P so
that all the props 60,60A extend to become set against the
roof.
It is possible to effect these operations entirely automatically as
will now be described. In this case the servo-pistons of the
control valve devices with a double suffix (11) are actuated but
these pistons effect the same operatives as the pistons bearing a
single suffix (1). Upon activation of the automatic control
sequence the valve 86 is connected to the pressure conduit P so
that pressure can be applied to the valves 65,65A via the conduit
96 to release these valves 65,65A. Thereby the chambers 60.sup.11
of the props 60,60A are connected to the return conduit R and thus
relieved. The servo-piston 69.sup.11 of the valve device 69 is also
subjected to pressure via a conduit 96.sup.1 so that the valve
device 69 operates to connect the chamber 60.sup.1 of the props
60,60A to the pressure conduit P so that the props retract. When
the valve 86 is subjected to pressure, the mechanism 88 is also
activated. After a pre-determined time interval, the mechanism 86
operates the valve 86 so that the conduit 96 is now connected to
the return conduit R and the pressure conduit P is connected, via
conduits 97,99 to the servo piston 79.sup.11 of the valve device
79. The valve device 79 then operates to connect the chamber
62.sup.1 of the ram 62 to the pressure conduit P to shift the
assembly. Pressure fluid in the chamber 62.sup.11 can discharge to
the return conduit R via the conduit 74, the valve 77 and the
conduit 78. When the shifting movement has ceased the flow of
pressure fluid in the conduit 82 decreases to zero and the
regulator 83 accordingly reduces the pressure in the conduit 84, to
relieve the servo-piston 85.sup.1 of the valve device 85. The valve
85 now operates to connect the conduit ST to the pressure conduit P
and the servo-pistons 63.sup.11, 63.sup.11 A of the valves devices
63,63A are subjected to pressure. The valve devices 63,63A operate
to connect the chambers 60.sup.11 of the props 60 60A to the
pressure conduit P so that the props 60,60A extend to become set
against the roof. When the pre-determined setting load of the props
60,60A is reached the pressure in a conduit 99.sup.1 connected to
the chambers 60.sup.11 of the props 60A reaches a sufficiently high
value to displace the servo-piston 73.sup.11 of the valve device
73. The valve device 73 now operates to connect the chamber
62.sup.11 of the ram 62 to the pressure conduit P to extend the
piston rod 61 and thereby displace the conveyor towards the mineral
face. When the pressure in the conduit ST reaches a pre-determined
value, the valve 89 also opens so that pressure is transmitted to
the control device S of the adjacent support assembly to initiate
the sequence for this assembly. It is possible to operate, for
example, five assemblies so that each assembly is automatically
shifted in succession.
FIG. 9 depicts a modified arrangement somewhat similar to FIG. 1
and like reference numerals denote like parts. In contrast to FIG.
1, the arrangement of FIG. 9 has no facility for automatic
operation. However, the arrangement has an apportioning device 101
connected to the chamber 62.sup.11 of the shifting ram 62. The
device 101 is connected to the main pressure conduit P and the
return conduit R and receives control pressure from a control
conduit 101.sup.1. The device 101 operates in accordance with the
pressure in the conduit 101.sup.1 to precisely control the flow of
pressure fluid to the chamber 62.sup.11 to thereby enable the
conveyor to be shifted by a pre-determined amount; such devices
known as per se. The arrangement of FIG. 9 employs similar
servo-control valve devices and working valves to the arrangement
of FIG. 1, and operates in the same manner as described
hereinbefore, when the device S is set into any of the positions I
- VII. Since the arrangement of FIG. 9 only operates manually, the
servo-control valve devices only have one servo-piston in contrast
to the arrangement of FIG. 1.
FIG. 2 depicts a further hydraulic control arrangement for a mine
roof support assembly with two relatively movable frames A,B. A,B
are each composed of two props 160,160A interconnected by floor and
roof rails. The numeral 160 denotes the front props nearest the
mineral face and the numeral 160A denotes the rear props. The
frames A,B are shifted in succession to advance the assembly by
means of a shifting ram 162 interconnecting the frames A,B The
control arrangement for the support assembly is somewhat similar to
that of FIG. 1 and is composed of valve devices 163 to 179 which
generally correspond to the valve devices of FIG. 1, and again the
suffixes (1) and (11) denote the servo-pistons of the servo valve
devices which, it will be recalled, effect the same operation on
the valve devices in question. The valve devices
163,165,167,168,169, 170 and 172 have two servo-pistons whereas the
valve devices 176,177, 178,179 only have a single servo-piston. In
function the valves 164,166,171,173 correspond to the working
valves 65,65A of FIG. 1, the valve devices 165,167,170,172
correspond to the control valve devices 63.sup.1, 63A of FIG. 1,
and the valve device 163 corresponds to the control valve device 69
of FIG. 1. No detailed description of these devices of their
interconnection is given since this has been discussed at some
length in connection with FIG. 1. In addition the arrangement of
FIG. 2 has a further valves 190-197, The valves 190,191,192,193,194
and 195 are non-return valves which can open in both directions
depending on the pressure conditions and the valves 196 and 197 are
non-return valves which can open in only one direction. The
arrangement also has two timing mechanisms 190,199 like 88 in FIG.
1 and regulators 206,108 like 83 of FIG. 1. In FIG. 2, there is
also a control device S (FIG. 4) which in this example has eleven
switching positions. The device S is connected to nine conduits
denoted 180 to 188 like 90-95 in FIG. 1.
The operation of the arrangement depicted in FIG. 2 is as
follows:
Position VI
With the device S set in position VI all the conduits 180 to 188
are connected to the return conduit R and the props 160, 160A of
both frames A,B are set against the roof. The chambers
162.sup.1,162.sup.11 of the ram 162 are non-pressurized. The valves
164,166,171 and 173 serve as pressure relief valves and open should
excess pressure occur in the associated chamber 160.sup.1 to allow
the pressure fluid in this chamber 160.sup.1 to discharge via
conduits 200 and into the return conduit R.
Position V
If the device S is set to position V the conduits 180,188 are
connected to the pressure conduit P. The valves 171, 173 are
subjected to control pressure via the conduit 180 and operate to
connect the chamber 160.sup.1 of the props 160, 160A of the frame A
with the return conduit R so that these chambers 160.sup.1 are
relieved of pressure. The servo-piston 163.sup.1 of the valve
device 163 is also subjected to pressure via the conduit 188 and
the valve device 163 operates to connect the chambers 160.sup.11 of
the props 160,160A of the frame A to the pressure conduit P. These
props 160,160A thus retract whilst the props 160,160A of the frame
B remain in the set roof-support condition. since there is no
connection between their chamber 160.sup.1 and the return
conduit.
Position IV
When the device S is set to position IV the conduits 180 and 183
are connected to the pressure conduit P. The valves 171,173 are
subjected to control pressure via the conduit 180 and operate to
connect the chambers 160.sup.1 of the props 160,160A of the frame A
with the return conduit R so that these chambers 160.sup.1 are
relieved of pressure. The servo-piston 169.sup.1 of the valve
device 169 is subjected to pressure via the conduit 183 and the
valve device 160 operates to connect the chamber 162.sup.1 of the
ram 162 to the pressure conduit P via a conduit 202. The ram 162
thus causes the frame A to be shifted in relation to the frame
B.
Position III
When the device S is set to position III the conduit 183 is
connected to the pressure conduit P so that the servo-piston
169.sup.1 of the valve device 169 is subjected to control pressure.
The valve device 169 operates to connect the chamber 162.sup.1 of
the ram 162 to the pressure conduit P, via the conduit 202. The ram
162 thus causes the frame A to be shifted in relation to the frame
B. The position III would be normally set after position V whereas
in contrast the cycle of operations performed by adopting position
V and then position III are performed together and move repidly by
adopting position IV. However, the provision of position III
enables the frame A to be shifted under load in which case position
V would be an unnecessary pre-requisite.
Position II
With the device S set to position II the conduit 181 is connected
to the pressure conduit P. The servo-pistons 170.sup.1,172.sup.1 of
the valve devices 170,172 are subjected to control pressure and
these valves 170,172 operate to connect the chambers 160.sup.1 of
the props 160,160A of the frame A to the pressure conduit P via the
conduit rod. The props 160,160A of the frame A thus extend and
become set against the mine roof.
Position I
If the device S is set to position I the conduit 182 is connected
to the pressure conduit P and pressure acts on the valves 166,171.
The valves 166,171 operate to connect the chamber 162.sup.1 of the
front props 160 of the two frames A and B to the return conduit R.
The valves 164,173 are not affected by control pressure since the
valves 190,193 are blocked. At the same time, the servo-piston
163.sup.1 of the valve device 163 is subjected to control pressure,
via a branch conduit 203, and the valve device 163 operates to
charge the chamber 160.sup.11 of the front prop 160 of the frames
A,B with pressure fluid from the pressure conduit P. The props 160
thus retract.
Position VII
When the device S is set to position VII the conduits 187,188 are
connected to the pressure conduit P. The valves 164,166 are
subjected to control pressure and to relieve the pressure in the
chambers 160.sup.1 of the props 160,160A of the frame B by
connecting the chambers 160.sup.1 to the return conduit R. The
servo-piston 163.sup.1 of the valve device 163 is also subjected to
pressure via the conduit 188 and the valve device 163 operates to
connect the chamber 160.sup.11 of the props 160, 160A of the frame
B to the pressure conduit. These props 160,160A thus retract whilst
the props 160,160A of the frame A remain in the set condition since
there is no connection between their chambers 160.sup.1 and the
return conduit R.
Position VIII
With the device S set in position VIII the conduits 184,187 are
connected to the pressure conduit P. The valves 164, 166 are
subjected to control pressure via the conduit 187 and operate to
connect the chambers 160.sup.1 of the props 160, 160A of the frame
B with the return conduit R so that these chambers are relieved of
pressure. The servo-piston 168.sup.1 of the valve device 168 is
subjected to pressure via the conduit 184 and the valve device
operates to connect the chamber 162.sup.11 of the ram 162 to the
pressure conduit P via a conduit 205. The ram 162 thus causes the
frame B to be shifted in relation to the frame A.
Position IX
With the device S set to position IX the conduit 184 is connected
to the pressure conduit P so that the servo-piston piston 168.sup.1
of the valve device 168 is subjected to control pressure. The valve
device 168 operates to connect the chamber 162.sup.11 of the ram
162 to the pressure conduit P to thus shift the frame B in relation
to the frame A. If position VII were not adopted before this
position IX the frame B would be shifted under load. The successive
setting of position VII and IX thus correspond to posiion VIII in a
similar manner that positions V and III correspond to position
IV.
Position X
With the device S set to position X the conduit 186 is connected to
the pressure conduit P. The servo-pistons 165.sup.1 167.sup.1 of
the valve devices 165,167 are thus subjected to control pressure
and these valves devices 165,167 operate to connect the chambers
160.sup.1 of the props 160,160A of the frame B to the pressure
conduit P via the conduits 200. The props 160,160A of the frame B
thus extend and become set against the mine roof.
Position XI
With the device S set to position XI the sequence of shifting
operations can be effected automatically as is now described.
In position XI the conduit 185 is connected to the pressure conduit
P and the timing mechanism 199 is thus subjected to pressure. At
the same time, the valves 164,166 are subjected to pressure, via a
branch conduit 185.sup.1 and the valve 178. The valves 164,166
operate to connect the chambers 160.sup.1 of the props 160,160A of
the frame B to the return conduit R to thereby relieve these props.
The servo-piston 163.sup.11 of the valve device 163 is also
subjected to control pressure via the branch conduits
185.sup.1,185.sup.11 and the valve device 163 operates to connect
the chambers 160.sup.11 of the props 160,160A to the pressure
conduit P. Thus the props 160,160A of the frame B are retracted.
After a pre-determined time interval the timing mechanism 199
actuates the valve 178 so that a conduit 204 is connected to the
conduits 185,185.sup.1 The servo-piston 168.sup.11 of the valve
device 168 is now subjected to control pressure and the valve
device 168 causes the chamber 162.sup.11 of the ram 162 to be
connected to the pressure conduit P via the conduit 205 and the
frame B is consequently shifted relative to the frame A. The
quantity of fluid flowing through the conduit 205 is monitored by
the regulator 206 and the regulator 206 controls the valve device
179. As soon as the fluid flow in the conduit 205, signifying the
end of the shifting step, ceases, the servo-piston 179.sup.1 of the
valve device 179 is pressurized and the valve device 179 is
actuated to connect the conduit 185.sup.1 to a conduit 128 via the
valve 178. This causes the servo-pistons 165.sup.11,167.sup.11 of
the valve 178. This causes the servo-pistons 165.sup.11,167.sup.11
of the valve devices 165,167 to be subjected to control pressure so
that these valve devices 165,167 operate to connect the chambers
160.sup.1 of the props 160,160A of the frame B to the pressure
conduit P. The props 160,160A thus extend and become set against
the roof again. During this sequence of operations, the valve 175
is also actuated by the pressure in the conduit 200, so that
pressure fluid flows from the conduit 218 to the conduit 207. The
timing mechanism 198 is thus initiated and the valves 171 and 173
are subjected to pressure via the valve 177. The valves 171,173 now
operate to connect the chambers 160.sup.1 of the props 160,160A of
the frame A to the return conduit R to relieve these chambers. The
valve 163 also charges the chambers 160.sup.11 of the props
160,160A of the frame A so that the props retract. After the
pre-determined time interval, the mechanism 198 acts to pressurize
the servo-piston of the valve device 177 and the valve device 177
operates so that the servo-piston 169.sup.11 of the valve device
169 is subjected to pressure. This causes the valve device 169 to
operate to connect the chamber 162.sup.1 of the ram 162 to the
pressure conduit P so that the frame A is shifted relative to the
frame B.
The quantity of fluid flowing through the conduit 202 is monitored
by the regulator 208 which controls the valve 176. As soon as the
flow of fluid in the conduit 202 ceases, signifying the end of the
shifting step, the valve 176 is actuated by the regulator 208 which
pressurizes the servo-piston of the valve 176. The valve 176 then
operates to cause the servo-pistons 170.sup.11,172.sup.11 of the
valve devices 170,172 to be subjected to pressure so that these
devices operate to connect the chambers 160.sup.1 of the props
160,160A of the frame A to the pressure conduit P. The props
160,160A thus extend to become set against the roof and one
shifting cycle is completed.
FIG. 3 depicts a modified part of a hydraulic control arrangement
for a mining installation where the shifting rams for a group of
support assemblies are operated simultaneously. In this arrangement
conduits 100,101 are laid along the mine working. By means of these
conduits 100,101 a group of valve devices 73 (see FIG. 1) are
controlled so that the shifting rams connected to the valve device
73 are operated simultaneously to displace the conveyor towards the
mineral face. For each group of support assmeblies, a non-return
valve 102 is installed in the conduit 100, to isolate the
associated group of valves 72 from the remaining valves.
FIGS. 5 and 6 illustrate how the various valve devices for each
support assembly can be formed into a convenient constructional
unit with the control device S. As shown, the device S is attached
to a plate 110 to which is also attached the various servo-control
valve devices designated 111 (for example, the valve device 73 in
FIG. 1) and the various working valves designated 112 (for example,
the valve 65.sup.1, FIG. 1). The various connections between the
individual valves and the device S denoted by conduits in FIGS. 1
and 2 are formed by bores 113 in the plate 110. The plate 110 is
also provided with ports 114,155 serving for connection to the main
pressure conduit P and the return conduit R, respectively.
FIGS. 7 and 8 depict a preferred form of servo-control device. As
shown, the valve device has a cylindrical housing 300 closed and
sealed at each end by screw-threaded caps 301,313. The housing 300
contains a number of items arranged in axial succession and held in
position by the caps 301,313 These items consist of a spacer bush
318, a valve seating 304, an apertured sleeve 308, a valve seating
305, an apertured sleeve 315, and a guide bush 320.
A closure element 306 in the form of a ball is engageable with the
seating 304 and similarly a closure element 307 in the form of a
ball is engageable with the seating 305. A plunger 311 is disposed
between the elements 306,307 and is guided in an axial bore
308.sup.1 provided in the sleeve 308. The construction is such that
when one valve 304,306 is open, the other valve 305,307 is closed
and vice versa. The plunger 311 is preferably constructed as
illustrated in the form of a diabolo so that the valve assemblies
304,306 and 305,307 can be opened and closed smoothly by gradually
increasing or decreasing the flow path through the assembly. The
element 306 is disposed in proximity to radial bores in the bush
318 and similarly the element 307 is disposed in proximity to
radial bores 315.sup.1 in the sleeve 315. Two servo-pistons 309,310
are slidably mounted in the guide bush 320 and sealed in relation
to the interior of the bush 320, by means of packing rings. The
interior of the bush 320 also defines chambers 316,317 into which
pressure medium can be admitted to cause displacement of the
pistons 309,310. The piston 309 is provided with an internal bore
accomodating a spring 312, which acts upon a plate 319 which in
turn acts upon the element 307. At the end of the housing 300
adjacent the cap 301 there is provided a member 314 which is
displaceably received in a recess 302 of the cap 301. The member
314 has a shaped end portion which engages the element 306 and a
spring 303 disposed in the recess 302 urges the member 314 towards
the element 306. The spring 303 acts on the member 314 to bias the
element 306 into sealing engagement with its seating 304 and
through the plunger 311, to bias the element 307 away from its
seating 305. The housing 300 contains bores denoted P and R which
are connectible directly or indirectly with the main pressure
medium conduit P and the return conduit R. The housing 300 also has
a bore denoted Z which would be connected to some consuming
appliance, for example, a shifting cam or hydraulic prop in the
arrangement of FIG. 1 or 2. The bore Z communicates with radial
bores 308.sup.11 in the sleeve 308. The housing 300 additionally
has bores, ST1, ST2 which would receive pressure fluid from the
manual and automatic control systems respectively (see FIGS. 1 and
2). The bore ST1 is connected to radial bores in the guide bush 320
which lead to the chamber 316. The bore ST2 leads into the chamber
317.
During normal operation, the valve 304,306 is closed as illustrated
so that the pressure bore P is blocked whilst the bore Z is
connected to the return bore R via the bores 308.sup.1, 308.sup.11
and the open valve 305,307. By applying pressure to either of the
bores ST1,ST2 one or other of the servo-pistons 309,310 is
displaced to move the inter-engaging components 307,311,306 against
the force of the spring 303 to open the valves 304,306 and close
the valve 305,307.
This enables the bore Z to be connected to the pressure bore P to
activate the associated appliance. If the pressure applied to the
bore ST1,ST2 in question decreases again, the spring 303 moves the
components, 307,311,306 back to their former position to open the
valves 305,307 and close the valve 304,306.
* * * * *