Abstract:
A gate valve includes a valve body and a spindle drive. The spindle drive has, at its one end, a wedge for blocking a pipe. The spindle drive includes a motor-driven spindle, wherein, wherein the spindle is connected by way of a coupling to a shaft in an axially displaceable manner, and the shaft has the wedge at its end.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority of European Patent Application EP 12 002 428.6 filed Apr. 3, 2012, the content of which is incorporated herein in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to a gate valve comprising a valve body and a spindle drive. The spindle drive has, at its one end, a wedge for blocking a pipe, wherein the spindle drive comprises a motor-driven spindle. 
         [0003]    A gate valve of the type mentioned in the introduction is known from the prior art. Such gate valves are built into pipes of different nominal sizes, wherein a pipe can be blocked by a gate valve. Such a gate valve comprises a valve body that is built into a pipe, which means that the pipe is flanged onto the valve body on both sides. A wedge is provided in the valve body, which is insertable into a corresponding wedge receptacle in the valve body via a spindle drive in order to block the pipe. As expressed by the term “wedge”, the wedge is hereby configured to be wedge-shaped in the direction of insertion into the wedge receptacle. In order to achieve a complete blocking, it is provided that the wedge and the wedge receptacle for the wedge have sealing elements on their facing surfaces. 
         [0004]    The spindle drive is mainly motor-driven. Such spindle drives must be very effective, which is more specifically embodied by the fact that the spindle of the spindle drive is mostly formed from a high strength tool steel. However, it is also known that highly corrosive media are transported in the pipes to be blocked. Tool steel has indeed high strength but it is not resistant to corrosion. 
       SUMMARY OF THE INVENTION 
       [0005]    Therefore, the object underlying the invention is to provide a spindle drive for a gate valve, which not only meets the requirements regarding corrosion resistance but also has the solidity required for a failure-free operation of a spindle drive. 
         [0006]    In order to solve the object, it is proposed according to the invention that the spindle is connected by a coupling in an axially displaceable manner to a shaft, wherein the shaft is connected to the wedge. Herein, “axially displaceable” means a displacement in the direction of the longitudinal axis of the spindle, respectively of the shaft. 
         [0007]    From this, it becomes clear that the part of the spindle drive that comprises the actual spindle is made of a high strength tool or screw steel, wherein the shaft, which is displaceable by the spindle, is manufactured from a corrosion resistant material, for example stainless steel. This means that two different components are coupled to each other by the coupling. Together with the drive, the spindle provides for the displacement of the shaft, the shaft transmits the axial movement of the spindle to the wedge in the area of the part of the valve body conducting the medium. 
         [0008]    It is more specifically provided that the coupling has a coupling bar with a sleeve, wherein the coupling bar is displaceably guided by at least one column extending parallel to the spindle drive. The coupling bar is thus not only a part of the connection of the two parts of the spindle drive, namely the actual spindle, which is drivable by a motor, and the shaft, at the end of which the wedge is attached, but the coupling bar also provides for a guiding of the spindle drive. 
         [0009]    Regarding the connection of the ends of the spindle and of the shaft by the coupling bar, the following must be mentioned: 
         [0010]    The sleeve of the coupling bar captures respectively the end of the shaft and of the spindle and connects them in such a manner that axial forces are transferable. The connection of the ends of the spindle and of the shaft by the sleeve of the coupling bar can hereby occur with a force or positive-fit. In a positive-fit connection, the ends of the spindle and of the shaft respectively have a circumferential groove, wherein the sleeve has corresponding protrusions on the inner side of the sleeve, which engage with the previously described grooves. In this respect, the sleeve in the coupling bar makes it possible to transfer axial forces such as occur for example when the wedge is pulled out of the wedge receptacle. Hereby, it is pointed out that neither the spindle nor the shaft rotate. Both parts merely execute a longitudinal movement. 
         [0011]    It has already been pointed out that the spindle drive comprises a motor-driven spindle. The motor drive comprises a motor and a screw drive that receives the spindle. 
         [0012]    Such a motor-driven spindle comes with a control that ultimately ensures that depending on a predetermined spindle path, the motor is stopped. If the control is defective, the wedge is pressed by the motor into the receptacle for the wedge in the pipe. Hereby, it can happen that the spindle drive bulges, with the consequence that the spindle drive is damaged. Due to the fact that the spindle is guided by the column extending parallel to the spindle drive during the movement of the spindle, a bulging can be avoided even in case of an over-rev of the drive. 
         [0013]    According to another advantageous feature, it is provided that the column has at least one bottom limit stop and preferably also a top limit stop for the coupling bar, which ensures that the wedge is not pressed by the spindle drive into the wedge receptacle in the valve body with an unduly high force, which would ultimately lead to damage or destruction of the seals therein. 
         [0014]    According to another feature of the invention, the coupling bar comprises two bar portions, which form a bushing in the area of the column, wherein the bushing comprises a slide or ball bearing. This makes it possible to have an essentially smooth and extremely precise guiding of the spindle drive by the column disposed on the body of the valve parallel to the spindle drive. 
         [0015]    The screw drive can be configured as a planetary or roller screw drive. It transforms the rotational movement of the drive motor into an axial movement of the spindle. Both types of screw drives are characterized by a high load capacity, great durability and great dependability. Furthermore, such drives have a very high repeat accuracy for small travelling distances. 
         [0016]    In the following, the invention is exemplarily described in more detail based on the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a cross-sectional of a gate valve in accordance with the present invention; 
           [0018]      FIG. 2  is a sectional view of the valve taken along line II-II from  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The gate valve  1  has the valve body  2 , which is inserted in a pipe  3 . The pipe  3  is flanged onto both sides of the valve body. The valve body  2  has a wedge receptacle  5  for receiving a wedge  10 . The wedge  10  is inserted in a sealed manner in the wedge receptacle, wherein seals  11  disposed on the wedge and seals  6  disposed on the wedge receptacle are provided for sealing. The spindle drive  20  is connected to the wedge  10 , which in the view according to the cross-section of the pipe has approximately a circular shape. The spindle drive  20  is mounted in a spindle head  22 . A screw drive  23  is provided in the spindle head  22  for holding the spindle, the spindle drive serving together with a motor (not shown) to drive the spindle  25  of the spindle drive. The spindle head  22  is connected to the valve body  2  by four columns  30  ( FIG. 2 ). The screw drive may be configured as a roller or as a planetary roller screw drive. The shaft  28  is adjacent to the spindle  25  and is connected with the spindle  25  of the spindle drive  20  via a coupling  29 . The spindle consists of a high strength tool or screw steel, whereas the shaft is formed from a corrosion resistant material, for example a stainless steel. 
         [0020]    As has already been explained, the spindle head  22  is connected with the valve body  2  by at least two, preferably four, columns  30  running parallel to each other. A coupling bar  31  is provided, which displaceably connects the spindle drive  20  with two columns  30 . In order to ensure a sliding of the coupling bar  31  on the column  30 , a bushing  35  in the form of a slide bearing or a corresponding ball or roll bearing ( FIG. 2 ) is provided in the coupling bar in the area of each column  30 . 
         [0021]    It has already been pointed out that the drive motor has a control, which ensures that when the wedge  10  has reached its end position in the wedge receptacle  5 , the motor (not shown) is stopped. In case the control malfunctions, a bottom limit stop  34   a  and a top limit stop  34   b  is provided in the area of the ends of at least one column  30 , against which the coupling bar  31  abuts when the motor attempts to over-rev the spindle. Thus it is prevented on the one hand that the wedge  10  is pressed with an excessive force into the wedge receptacle  5 , which would damage at least the seals  6 ,  11  or even the entire wedge or the wedge receptacle in the valve body. 
         [0022]    On the other hand, the coupling bar prevents the spindle drive  20  from bulging in case of an over-rev of the motor. This means that the coupling bar stabilizes the spindle drive more specifically in case the control for stopping the spindle drive does not stop the drive after having travelled along determined path. 
         [0023]    Furthermore, the coupling bar  31  forms the coupling together with a sleeve  32  disposed in the area of the ends of the shaft and of the spindle. The two ends of the spindle and of the shaft are held together by the sleeve of the coupling bar so that they transfer a force in the axial direction ( FIG. 2 ). To this end, the two portions  33  of the coupling bar  31  are connected to the sides of the sleeve  32  by a screw connection  39 . 
         [0024]    Regarding the connection between the spindle and the shaft, which transfers a force in the axial direction, the following must be explained. The ends of the spindle and of the shaft stand above each other so that they are aligned. In the area of the sleeve  32  of the coupling bar, the shaft and the spindle both have a groove, more specifically a circumferential groove  36 ,  37 . The sleeve engages with these grooves with corresponding protrusions (not shown), so that a positive-fit connection is formed by the sleeve of the coupling bar between the spindle and the shaft. 
       LIST OF REFERENCE NUMBERS 
       [0000]    
       
           1  gate valve 
           2  valve body 
           3  pipe 
           5  wedge receptacle 
           6  seal 
           10  wedge 
           11  seal 
           20  spindle drive 
           22  spindle head 
           23  screw drive 
           25  spindle 
           28  shaft 
           29  coupling 
           30  column 
           31  coupling bar 
           32  sleeve 
           33  portions 
           34   a  bottom limit-stop 
           34   b  top limit-stop 
           35  bushing 
           36  circumferential groove in the spindle 
           37  circumferential groove in the axis 
           39  screw connection for the bar shells