1. Technical Field
That problem is solved according to the invention by the drive means and by the slide valve in accordance with the claims recited herein. The invention is based on the concept of providing for a slide valve a drive means that has two parallel spindles, especially each having a trapezoidal thread, which are driven in rotation by a motor. The drive means has travelling nuts which engage the spindles and are movable in the longitudinal direction of the spindles by rotation of the spindles, and a cross-yoke which is arranged transversely with respect to the spindles and is connected to the travelling nuts on the one hand and to a rod on the other hand. The rod is arranged in parallel between the spindles and is connected or connectible to a slide plate, the rod being axially movable by the motor for the actuation of the slide plate. The travelling nuts and the rod are each articulatedly connected to the cross-yoke, for example by way of pivot pins and by way of guide slots and sliding blocks. By virtue of those articulated connections of the travelling nuts and the rod to the cross-yoke, a skewed position of the cross-yoke, which can occur, for example, if the two travelling nuts do not operate synchronously or if the two spindles have not been mounted exactly in parallel, is compensated for. The articulated connections allow a rotational movement of the cross-yoke out of its normal position perpendicular to the spindles into a skewed position, without giving rise to significant moments that result in canting of the yoke or jamming of the travelling nuts. Since both the travelling nuts and the rod are articulatedly connected to the yoke, the cross-yoke can rotate freely on the input and output sides. It will be understood that the rotational movement of the cross-yoke is not entirely free, but is limited by the geometry of the spindle arrangement. Canting is in any case adequately prevented by the articulated connection, which improves reliable operation of the slide valve and largely avoids downtimes.
2. Description of Related Art
For controlling flows of gas and solids in the iron and steel industries and also in the chemical and petrochemical industries it is known to use slide valves which have a slide plate displaceably mounted in a housing, which slide plate unblocks or closes a valve opening in the housing by means of a stroke movement. Such valves are intended to allow long maintenance-free operating times at high operating temperatures, large nominal diameters and high numbers of switching operations. In addition, it is generally required that the overall height of the valves be low.
As regards the drive means of the slide plate, hydraulic or electromechanical systems are known. An example of an electromechanical system is described in U.S. Pat. No. 4,054,261, which is mentioned at the beginning. That drive means comprises a double-spindle system having a common drive motor which, by way of an angular gear, causes the two spindles to perform synchronous rotational movements. On the spindles, which are arranged in fixed position, there are arranged travelling nuts which are fixedly connected to a cross-member. Movement of the spindles causes the travelling nuts and the cross-member to move in the longitudinal direction of the spindles. The cross-member is in turn connected to two push rods which are attached to the distal end of the slide plate. The movement of the cross-member effects the stroke movement of the slide plate that is required to open and close the slide valve.
If the synchronous operation of the two spindles is interrupted, the position of the two travelling nuts relative to one another is altered and the cross-member becomes canted. The jammed drive means is unable to operate, resulting in expensive downtimes. Canting of the cross-member may also occur if, during the stroke movement of the slide plate, force is introduced asymmetrically into the cross-member, with the result that different forces act on the travelling nuts.
A further slide valve for industrial valve fittings is known from U.S. Pat. No. 4,253,483, in which a spindle is arranged on each side of a pipe duct in the slide valve. The travelling nuts seated on the spindles are connected to telescopic tubes which are attached to a slide plate. During the stroke movement for closing or opening the valve the telescopic tubes are pulled over the spindles, so that the spindles and the telescopic tubes are arranged concentrically. The manufacturing outlay for such telescopic systems is relatively great, especially when it is considered that the two telescopic tubes each require their own guide means.
Further spindle drive means for slide valves are known, for example, from DE 1 898 716 U1, which originates from the applicant, and WO 2010/111188 A2. Both cases involve single spindles which are connected by way of a travelling nut to a telescopic tube which, in turn, is connected to the slide plate. Such single spindles need to be of relatively large dimensions in order to be able to transfer the forces required for the stroke movement of the slide plate.