Abstract: A shaking control unit for a hydraulic cylinder, wherein a first predetermined pressure is admitted to the piston space of the cylinder through a first hydraulic line. A three/two-way valve connects in its zero position a second hydraulic line to a return tank, the second hydraulic line being connected to the first hydraulic line through a check valve. A first control line leads from the first hydraulic line to a first control area of the three/two-way valve. A second control line leads from the second hydraulic line to a second control area of the three/two-way valve. The three/two-way valve is constructed in such a way that, when the pressure in the first hydraulic line reaches a second predetermined pressure which is greater than the first predetermined pressure, the three/two-way valve switches and connects the first hydraulic line to the second hydraulic line. If the piston of the hydraulic cylinder meets an obstacle, the pressure in the first hydraulic line rises above a certain limit value.

Abstract: A shaking control unit for a hydraulic cylinder, wherein a first predetermined pressure is admitted to the piston space of the cylinder through a first hydraulic line. A three/two-way valve connects in its zero position a second hydraulic line to a return tank, the second hydraulic line being connected to the first hydraulic line through a check valve. A first control line leads from the first hydraulic line to a first control area of the three/two-way valve. A second control line leads from the second hydraulic line to a second control area of the three/two-way valve. The three/two-way valve is constructed in such a way that, when the pressure in the first hydraulic line reaches a second predetermined pressure which is greater than the first predetermined pressure, the three/two-way valve switches and connects the first hydraulic line to the second hydraulic line. If the piston of the hydraulic cylinder meets an obstacle, the pressure in the first hydraulic line rises above a certain limit value.

Abstract: A method in underground coal mining for separating the upper coal of the seam from the roof during the advancement of the upper sliding cap of a support frame, wherein the front edge of the cap is forced in a plane of the cap between the upper coal to be separated and the rock from which the coal is to be separated. During the advancement of the sliding cap, the sliding cap is alternatingly moved backwardly and forwardly, so that the from edge of the sliding cap separates the upper coal during its forward movement. Alternatively or additionally, when the front edge of the sliding cap contacts the upper coal, alternatingly higher and lower pressure can be admitted to the sliding cap in order to obtain a shaking effect. In this combined method, the sliding cap is advanced, the shaking procedure is carried out as the front edge contacts the upper coal, and the sliding cap is subsequently moved backwardly. The cycle is then repeated several times.

Abstract: A three-port, two-position electrohydraulic valve has an elongated valve member reciprocatably guided in a bore of the valve housing only by two sealing rings of small friction and including only two further sealing rings cooperating with sealing edges respectively provided on the valve member and the housing for controlling fluid flow between the three ports. The valve member is reciprocated between two end positions against the force of a return spring by an electromagnet. Such a valve requires only small forces for reciprocation of its elongated valve member, so that a small electromagnet is sufficient.The valve of the present invention favorably differs from known electrohydraulic three-port, two-position valves which are constructed as seat valves and operated in opening direction by an electromagnet of long stroke and which require also considerable forces during operation, due to large friction forces inherent with seat valves.

Abstract: An improved control for an underground mining working support unit arrangement of the type having an adjacent support unit arrangement hydraulically connectable to the working support unit arrangement in which a plurality of hydraulic supports support load points, it is disclosed wherein the hydraulic supports are successively connectable to several of the load points with a reversing valve operable to alternately connect control valves to selected hydraulic supports.

Abstract: An improved valve in use for underground mining in connection with a piston cylinder unit, such as a hydraulic prop, is disclosed. The valve includes a piston member within a control chamber which is operative to terminate fluid communication between the hydraulic prop and a hydraulic fluid source. The piston is pressure-equalized in a neutral position when the hydraulic prop is set.

Abstract: An excess pressure valve particularly for props having telescopic parts which are extensible or retractable by fluid under pressure used in underground mining operations, comprises a valve housing having a bore therethrough with a connection end connectable to the fluid under pressure and an opposite opened end. A tubular sleeve is slidable in the bore and has a passage therethrough for the fluid under pressure and it has an annular inlet end face facing the connection end and an opposite annular pressure end face which opposes a piston which is also slidable in the bore between the sleeve and the opened end. The fluid under pressure maintains the sleeve and the piston in slightly spaced relationship so that there is a small space therebetween which is sealed by an annular pressure seal.