Change-over valve for hydraulic walking mine-roof supports

A change-over valve for hydraulic walking mine-roof supports comprises a valve housing containing a sealed-off operating piston in which a valve member supported on a helical spring is displaceably arranged, the piston being responsive to the supply of small quantities of hydraulic fluid through an end connection in the housing and having a sealing cone adapted to close a connection of large throughflow cross-section at the opposite end of the housing which also has a side connection for the supply of pressurized fluid to a working cylinder of a mine-roof support, the large throughflow cross-section at the connection thereby guaranteeing brisk pushing-in of a piston rod of a piston in the cylinder.

This invention relates to a change-over valve for hydraulic walking 
mine-roof supports. 
Change-over valves can be used to supply pressurised fluid--which is 
received alternately from different inlet conduits--through one specific 
outlet. Such a valve is used for example in the control system of 
hydraulic walking mine-roof supports wherein one side of a piston in a 
woring cylinder is charged alternately with pressurised fluid by way of 
two different control valves. Known change-over valves (see, for example, 
DE-PS-3,304,983) according comprise a valve housing with two connections 
for the supplied pressurised fluid and one connection for the pressurised 
fluid outlet. Between the connections for the supplied pressurised fluid, 
or between two sealing seatings associated with these connections, the 
valve housing has a closure body which is pressed by the inflowing 
pressurised fluid in each case on to a sealing seating lying opposite to 
the inflow side. The closure body closes the pressureless connection and 
prevents the transfer of inflowing pressurised fluid to the second control 
valve which, in this operational position, is generally connected with the 
return conduit connected to a fluid reservoir. The actuation movement and 
the application pressure result from the fluid flow of the pressurised 
fluid supplied to the valve. If the inflow is only slight, then the 
closure body is no longer pressed on to the sealing seating and the 
supplied pressurised fluid flows in short circuit away to the pressureless 
connection. This condition can occur, for example, in the control of the 
hydraulic advancing cylinders of walking mine-roof supports which are 
connected to a conveyor. The advancing cylinders serve to press the 
conveyor forwards during winning of the mineral from the working face of 
the mine into the cleared space in front of that working face and also to 
draw up the walking mine-roof supports after the winning operation. 
A particular problem arises however in the operation of the advancing 
cylinders of hydraulic walking mine-roof supports, especially during 
winning of mineral by "skimming" when the pressing-forward of the conveyor 
takes place slowly, that is to say, with a small supply of pressurised 
fluid. On the other hand, the "drawing-up" of the supports should take 
place quickly, which means that pressurised fluid previously introduced 
into the advancing cylinders during the pressing forwards of the conveyor 
should flow away again as far as possible without hindrance through a 
passage of large cross-section. In the pushing forwards of the conveyor, 
all the advancing cylinders of the walking mine-roof supports are 
simultaneously charged with pressurised fluid so that the quantity of 
hydraulic fluid supplied to each advancing cylinder per unit of time is 
comparatively small and does not suffice to actuate a connected 
change-over valve in a sealed manner. Conversely, the supplied pressurised 
fluid should flow away through a passage of the largest possible 
cross-section. The change-over valves used hitherto are not very suitable 
for this purpose, since the closure body does not assume a defined 
operational position during flowing back of the hydraulic fluid. 
The aim of the present invention accordingly is to devise a change-over 
valve wherein the closure body assumes a stable and defined operational 
position even in the case of a small inflow of pressurised fluid and 
wherein a passage having a large throughflow cross-section is available 
for the outflowing pressurised fluid. 
With this aim in view, the invention is directed to a change-over valve for 
hydraulic walking mine-roof supports, comprising a valve housing having 
three fluid-flow connections connectable to hydraulic control valves, 
hydraulic working cylinders or other parts of mine-roof supports, with one 
of the connections being arranged on a side of the housing and the other 
two connections at the ends of the housing, and a closure body which is 
axially displaceable in a central bore of the valve housing and which is 
chargeable with supplied pressurised medium during operation of the valve 
for the alternate connection of two connections while the third connection 
is closable as a result of the closure body being pressable on to a valve 
seating, in which: 
(a) the closure body is formed as a generally cylindrical operation piston 
and is sealed off by means of a gasket or other seal in the housing bore; 
(b) the piston forming the closure body has a sealing cone at one end; 
(c) at the other end of the piston there is a longitudinal blind bore from 
which radial bores branch out; and 
(d) in the longitudinal bore of the piston a valve member is supported for 
axial displacement on a spring so that, under the pressure of the spring, 
it closes the opening in a hollow cylindrical bush which is sealingly 
inserted in the outer portion of the longitudinal bore of the piston. 
A change-over valve in accordance with the invention therefore has an 
operating piston which is sealed off on its outer circumferential surface 
and which has an internal valve member supported on a spring on the fluid 
inflow side. In the case of a small supply of fluid, the piston shfts 
axially and closes a passage with a large throughflow cross-section on the 
opposing connection with a sealing seating. As the pressure of the 
pressurised fluid builds up before the valve member, it reaches a pressure 
head in excess of the pressure of the spring so that it opens the valve 
member and flows into the pressure chamber of the connected working 
cylinder. In the opposite direction the pressure fluid flowing out of the 
working cylinder presses the piston into the other open position which has 
a large throughflow cross-section.

The illustrated change-over valve is arranged to be charged with 
pressurised fluid on two sides for the charging of one piston side of an 
advancing cylinder in an hydraulic walking mine-roof support. The valve 
has a cylindrical housing 1 provided with a central graduated or stepped 
bore 2 in which a cylindrical operating piston 3 is displaceable guided 
for axial movement. On the outer circumferential surface of the piston 3 a 
gasket or other annular seal 4 is inserted into an annular groove (not 
designated) so as to seal off the gap between the piston 3 and the wall of 
the bore 2. 
The bore 2 merges at the two ends of the valve housing 1 into two fluid 
connections 5 and 6, the connection 5 being machined into a valve insert 7 
inserted into the bore 2 an having a frusto-conical sealing seating 8 for 
the piston 3. The sealing surface of the sealing seating 8, designated by 
A.sub.2, is smaller than the cross-sectional surface A.sub.1 sealed off by 
the gasket 4 on the piston 3. The piston 3 has a sealing cone 9 on its end 
which engages the sealing seating 8. On the side of the valve housing 1 
there is a radial connection 10 which opens in the region of the sealing 
cone 9 into the central bore 2 of the change-over valve. 
A longitudinal blind bore 11 having a shoulder or step between its ends is 
formed in the piston 3 so as to extend from that end adjacent the 
connection 6 and remote from the sealing cone 9. From this bore radial 
bores 12 branch outwards in star formation. The radial bores 12 are 
covered in one operating position of the piston 3 by the wall of the bore 
2, but in another operating position of the piston they open into the 
connection 10. In the deepest part of the longitudinal bore 11 there is a 
helical compression spring 13 which acts on a valve member 14 so as to 
press it into sealing engagement with an inner end of a hollow cylindrical 
bush or sleeve 15 inserted into the longitudinal bore 11 from that end 
adjacent the connection 6. The valve member 14 is guided in a cage 17 
having radial bores 16. On the outer circumferential surface of the bush 
15 there is a gasket 18, while 19 designates a vent bore. 
The change-over valve thus illustrated is intended to control an hydraulic 
working cylinder 20 of an hydraulic walking mine-roof support. The 
cylinder has a piston 22 which is displaceable on a piston rod 21 and 
which abuts at the end of the piston rod 21 on a collar ring 23. The 
working cylinder 20 is connected beneath the piston 22 and the piston rod 
21 through the conduit 24 with the connection 10 of the change-over valve. 
The annular space of the working cylinder 20 above the piston 22 is 
connected by the conduit 25 to a directional control valve 26 having three 
ports and two distinct positions of operation so as to connect the valve 
26 alternately to a high pressure conduit P and to a return conduit T 
leading to a fluid reservoir. 
The connections 5 and 6 of the change-over valve are connectable 
alternately to directional control valves 27 and 28 each having three 
ports and two distinct positions of operation and each chargeable with 
high pressure fluid from the high pressure conduit P. The connection takes 
place through the conduit 29 from the directional control valves 27 to the 
connection 5 and through the conduit 30 from the directional control valve 
28 to the connection 6. A constriction or throttle 31 provides a small 
throughflow quantity. The change-over valve is without pressure in the 
operational position illustrated since all the 3/2 directional control 
valves 26, 27 and 28 are opened through the return conduit to T. 
Pressurised fluid flows through the 3/2 directional control valve 28, which 
is open to the high pressure conduit P, by way of the conduit 30 to the 
piston 3. Since the quantity of supplied fluid is only small, the sealed 
piston 3 is displaced towards the sealing seating 8 without the build-up 
of a pressure before the valve member 14. After the sealing cone of the 
piston 3 has come to abut on the sealing seating 8, the pressurised fluid 
builds up before the valve member 14, thereby causing the pressure to 
build up. When a pressure head sufficient to overcome the spring 13 is 
reached, the valve member 14 moves into an "open" position whereby the 
pressurised fluid flows by way of the bores 16 and 12 to the connection 10 
and further, by way of the conduit 24, to beneath the piston 22 and the 
collar ring 23 of the piston rod 21, which is therefore moved outwardly. 
On the other hand, the piston rod 21 can be charged with pressurised fluid 
from the 3/2 directional control valve 27 by way of the conduit 29 through 
the connection 6. The pressurised fluid arriving on the sealing cone 9 
lifts the piston 3 away from the sealing seating 8 and displaces it 
towards the connection 6, whereby the throughflow cross-section to the 
connection 10 is cleared for the passage of fluid to the conduit 24. 
The piston 21 of the working cylinder 20 is driven in again when the piston 
22 is charged with pressurised fluid from the directional control valve 26 
through the conduit 25. The pressurised fluid present in the pressure 
chamber beneath the piston 22 is then forced out through the conduit 24 to 
the connection 10. It presses upon the annular area A.sub.1 -A.sub.2 on 
the piston 3, which results from the difference of the cross-sectional 
area A.sub.1 of the piston and the sealing area A.sub.2 on the sealing 
cone, and displaces the piston 3 in the direction towards the connection 6 
so that the pressurised fluid flows away by way of the large throughflow 
cross-section at the connection 5 through the conduit 29 to be opened 3/2 
directional control valve 27 towards T and into the return conduit.