Patent Publication Number: US-10787798-B2

Title: Shut-off element and hydrant with such a shut off element

Description:
The present invention relates to a shut-off element and a hydrant. Hydrants are connected to a water distribution system and provide a faucet for extracting water, thus enabling the fire brigade as well as public and private users to extract water from the water distribution system. The network pressure in the water distribution system is typically about 6-9 bar. Hydrants comprise a riser with an interior and an exterior, wherein the water distribution system is usually connected via a bottom-side inlet pipe to the interior. The water is extracted via lateral connections from the interior. 
     For opening and closing hydrants, shut-off elements are known which can be arranged in the region or near the inlet pipe. Shut-off elements are, for example, hydrant main valves that comprise an axially adjustable main valve body, which can be closed by a sealing surface of the hydrant. Alternatively, the main valve body can be sealed off by a main valve seat removable from the hydrant. The main valve body is a sealing element, which seals with the sealing surface of the hydrant in a closed position and releases a connection between the bottom inlet pipe and the interior of the riser in an open position. The shut-off element further comprises a valve rod connected to the main valve body, via which valve rod the main valve body can be transferred from the closed position to the open position and vice versa. The valve rod is usually arranged axially in the riser of the hydrant and can be adjusted manually. Thereby, a manual rotation is transferred to an axial adjustment by means of an actuating element, for example a spindle, via which the valve rod and thus the main valve body are axially moved up and down. 
     A problem in the prior art is that pressure surges occur when closing the hydrant. The intensity of a pressure surge increases with increasing speed of the shut-off element. The pressure surge problem often leads to pipe breaks in the water distribution system, which has serious consequences. In addition to the problem of large water loss in the water distribution system and the decreasing water pressure, additional problems namely occur in relation to drinking water pollution as well as in relation to damage to terrain or roads. High pressure surges can also result in burst of a fire-fighting hose, for example. Due to the pressure surges there is also the danger that water from the hose can be pushed back into the water distribution system, whereby slop and/or extinguishing foam can get into the drinking water. 
     To solve the problem, it is known in the art that the shut-off element of the hydrant is to be closed slowly. For this purpose, it is proposed in the prior art to make the last turn to close the shut-off element slowly when closing the hydrant, since the largest change in the amount of water occurs when the valve is almost closed. A problem with this solution, however, is that this measure may fall into oblivion in an urgent firefighting, for example, or was not even known due to insufficient instructions of the operator. It is therefore an object of the present invention to propose a shut-off element which does not cause high pressure surges even when closing quickly. It is a further object of the present invention to provide a hydrant with such a shut-off element. 
     The aforementioned object is achieved by a shut-off element according to the independent claim  1  as well as a hydrant according to the independent claim  17 . Further advantageous features emerge from the dependent claims. 
     According to the invention, the above-mentioned object is achieved by a shut-off element of a hydrant with a hydrant axis, wherein the shut-off element comprises a valve rod, which is axially movable substantially along the hydrant axis, and a main valve body, which can be brought into sealing engagement with a sealing surface of the hydrant. The shut-off element further comprises a damping system, which is arranged in-between the main valve body and the valve rod or in a portion of the valve rod or in-between an actuator of the valve rod and the valve rod or in the actuator itself such that the main valve body is coupled with the valve rod via the damping system axially damping along the hydrant axis. 
     As a result, a shut-off element is provided by a simple solution in which, regardless of the speed with which an operator closes the shut-off element via the actuating element, the main valve body of the shut-off element seals the hydrant with a nearly decoupled speed. The speed with which the main valve body comes into sealing engagement with the sealing surface of the hydrant when closing, is slowed down by the damping effect of the damping system, particularly from a position shortly before the closed position, whereby pressure surges are greatly reduced. In the open position, the main valve body is advanced a bit in relation to the valve rod. When transferring the main valve body to the closed position (upward movement), the main valve body follows this upward movement at a reduced speed, i. e. damped. With this reduced speed, the shut-off element is finally closed, this speed being adjustable (reducible) in such a way that high pressure surges are prevented. The damping system is arranged between the main valve body and the lower end of the valve rod or is between the actuator, for example a spindle, and the upper end of the valve rod. The damping system may alternatively be interposed in a portion of the valve rod. Further alternatively, the damping system can be interposed in the actuator itself. The actuator may be coupled at one end to the valve rod and configured to translate a torque applied at a further end of the actuator into an axial movement of the valve rod. 
     The actuator may include a spindle bearing, a spindle and a spindle nut. 
     Advantages of the present invention comprise: 
     There are no pressure surges in the hydrant—regardless of the speed with which the hydrant is closed. 
     The main valve body is retracted in the sealing surface of the hydrant at closing with a speed almost decoupled from the manual operation. Thus, the shut-off element is tracked only delayed also when closing rapidly in a manual fashion and thereby guaranteeing a slow shut-off or closing of the hydrant. 
     The structure of the inventive shut-off element is kept particularly simple. As a result, maintenance work is kept at a minimum and thus the costs can be kept low overall. 
     The damping system can be retrofitted. For this purpose, the damping system can be inserted subsequently between the lower end of the valve rod and the main valve body only, or between the actuating element and the upper end of the valve rod. Alternatively, the damping system can be subsequently interposed in a section of the valve rod. Furthermore alternatively, the damping system can be subsequently interposed in the actuating element itself. This allows a simple extension. 
     The damping system works with the pressure difference of the water in the inlet pipe and in the riser pipe. In the open position of the shut-off element, the clamping force of a compression spring of the damping system exceeds the difference in the forces in the opposite direction, generating the force difference by the respective pressure difference between the bottom and the top of the main valve body. This pressure spring acts on a piston section of the main valve body which is movably arranged in a cylinder space. Thus, the piston section of the main valve body is axially moved a bit out of the cylinder chamber of the damping system in the open position by means of the clamping force of the compression spring. 
     When closing the hydrant, with increasing approach of the main valve body to the sealing surface of the hydrant, the difference of forces steadily increases that are applied to the bottom and to the top of the main valve body, respectively. This force difference outweighs the resilience of the compression spring in the damping system so that it is compressed again. Thus, the piston section of the main valve body is retracted again into the cylinder chamber of the damping system. However, this movement is performed softly. For this purpose, a fluid must flow through a reducing element in the cylinder chamber, reducing the flow velocity of the fluid by the reducing element, with the result that the backflow of the fluid from the cylinder chamber into a designated fluid reservoir is slowed down or damped, respectively. This has the consequence that the main valve body only slowly retracts and thus only slowly reaches the closed position. In that the main valve body only very slowly retracts into the sealing surface of the hydrant, pressure surges are thus reduced advantageously. 
     The reducing element allows the adjustment of the flow rate at which the fluid is transferred from the cylinder chamber into the fluid reservoir. Thus, the flow rate can be advantageously adjusted. Because of this, the speed can be adjusted at which the main valve body is to be transferred into the closed position. 
     The reducing element may comprise a pin, which is inserted some distance into a return line so that the flow-through cross-sectional area of the return line is reduced. The fluid must flow through an annular space thus formed between the outer surface of the pin and the inner surface of the return line in the axial direction along the pin. The annular space or flow-through cross-sectional area of the return line can be adjusted by appropriate selection of the outside diameter of the pin and/or the inner diameter of the return line. Additionally, or alternatively, the length of the path along which the fluid flows through the annular space can be adjusted. For this purpose, the pin can be threaded deeper into the return line or retracted. The deeper the pin is retracted into the return line, the stronger the reflux of the fluid from the cylinder chamber into the fluid reservoir is inhibited, with the result that the main valve body is transferred into the closed position at a reduced speed. 
    
    
     
       The shut-off element according to the invention will be explained in more detail based on exemplary embodiments and corresponding drawings which are not intended to limit the scope of the present invention. Showing: 
         FIGS. 1 a, b   : a sectional view of a portion of a shut-off element of a hydrant in a first, closed valve position and an enlargement thereof; 
         FIGS. 2 a, b   : a sectional view of the portion of the shut-off element in a second, partially open valve position and an enlargement thereof; 
         FIGS. 3 a, b   : a sectional view of the portion of the shut-off element in a third, fully open valve position and an enlargement thereof; 
         FIGS. 4 a, b   : a sectional view of the portion of the shut-off element in a fourth, almost closed valve position and an enlargement thereof; and 
         FIGS. 5 a - d   : each show an enlargement view of the damping system in different positions of the shut-off element according to  FIGS. 1 a    to  4   b.    
     
    
    
     In the following, preferred embodiments of the shut-off element according to the invention and the hydrant are described in detail. The figures each show a sectional view of a hydrant  100  in different valve positions together with respective enlargements thereof. The hydrant  100  comprises a shut-off element  102 , which comprises a valve rod  104  and a main valve body  106 , which is brought into sealing engagement with a sealing surface  108  of the hydrant  100  according to  FIGS. 1 a, b   . The shut-off element  102  further includes a damping system  110 , which is interposed in the embodiment shown in the figures between the valve rod  104  and the main valve body  106 . In other words, the main valve body  106  is coupled via the damping system  110  axially movable with the valve rod  104 . Although not shown in the figures, the damping system can be arranged between the actuator element, for example a spindle, and the upper end of the valve rod  104 , or interposed in a section of the valve rod. Further alternatively, the damping system can be interposed in the actuating element itself. The actuating element may be capable of converting a torque applied at one end of the actuating element in an axial movement of the valve rod. For this purpose, the actuating element may comprise a spindle bearing, a spindle and a spindle nut. The respective enlargement views of the figures, i.e.  FIGS. 1 b , 2 b , 3 b  and 4 b   , show the damping system  110  in greater detail. The hydrant  100  has a hydrant axis A-A arranged vertically there. The hydrant axis A-A can also be arranged deviating from the vertical axis (not shown). 
     The damping system  110  is preferably designed as a spring-loaded damping system which allows a return or retraction of a piston section  114  of the main valve body  106  in the direction of the damping system  110  with reduced or damped movement. For this purpose, the damping system  110  comprises a compression spring  112  which is inserted biased at least between the damping system  110  and the piston section  114  of the main valve body  106 . In the unloaded state, the compression spring  112  applies a compressive force between the damping system  110  and the piston section  114  of the main valve body  106 . As a result, a compressive force is applied on the main valve body  106  for squeezing out or extending the piston section  114 . As soon as a force predominates in the direction opposite to the direction of the pressure force from the pressure spring  112 , the piston section  114  of the main valve body  106  is retracted, as explained in detail below. 
     The main valve body  106  comprises an upper piston section  114 . In the embodiment shown in the figures, the piston section  114  is a separate component from the main valve body  106 , which is connected to the upper side of the main valve body  106  via a fastening element  116 , for example a pin connection  116 . Although not shown, the piston section  114  may be integrally formed with the main valve body  106 . In the embodiment shown, the piston section  114  is inserted in a cylinder chamber  118  of the damping system  110  in an axially movable manner. For sealing the cylinder chamber  118  relative to the outside, a first annular seal  120  is provided, which is preferably inserted into an annular groove of the piston section  114 . 
     The damping system  110  further includes a fluid reservoir  122 , which is received in an internal space of the valve rod  104  in the embodiment shown. The damping system  110  further includes a pipe body  124  in which an inflow conduit  126  and a return pipe  128  are disposed. The inflow pipe  126  permits an inflow of a fluid  130  stored in the fluid reservoir  122  into the cylinder chamber  118 . In this case, the fluid  130  flows via the inflow pipe  126  and a check valve  132 , which only allows the inflow of the fluid  130  into the cylinder chamber  118 , but not its reverse flow in the reverse direction. This return flow is only possible via the return pipe  128 . For this purpose, in the embodiment shown, the fluid  130  flows from the cylinder chamber  118  via an annular gap  133  which is formed between an inner surface of a housing portion of the damping system  110  and an outer surface of the pipe body  124 , and then through an opening  134  or a bore in the pipe body  124  (or arranged therein) of the return pipe  128  and flows from there via the return pipe  128  into the fluid reservoir  122 . The annular gap  133  also serves to receive the pressure spring  112 . 
     To reduce the flow rate of the fluid  130  at reflux, a pin  135  is inserted at least in sections along the length of the return flow pipe  128 . The pin  135  reduces the cross-sectional area of the return flow pipe  128  to only one annular space  154  between the outer surface of the pin  135  and the inner surface of the return pipe  128 . Due to this reduced cross-sectional area, the fluid  130  flows back into the fluid reservoir  122  at a greatly reduced flow rate. Thus, the cylinder chamber  118  can escape only with delay when applying a strong force to the bottom of the main valve body  106 . Since the fluid  130  is incompressible, the main valve body  106  is consequently retracted into the damping system  110  at a reduced speed (shock absorber principle). Hereby, the main valve body  106  advantageously closes only very slowly with the sealing surface  108  of the hydrant  100 , and substantially independent or nearly decoupled from the speed at which the valve rod  104  is moved upward. Due to this reduced speed with which the hydrant  100  is closed, pressure surges are eliminated or significantly reduced in their amplitude when closing the hydrant  100 . 
     In the following, the sequence between the opening and closing of the shut-off element  102  will be explained.  FIGS. 1 a, b    show the shut-off element  102  in its closed position. In the closed position, the main valve body  106  is in sealing engagement with the sealing surface  108  of the hydrant  100 , and the piston section  114  of the main valve body  106  is fully retracted into the damping system  110 .  FIGS. 2 a, b    show the shut-off element  102  in the course of opening. More specifically, the shut-off element  102  is shown in  FIGS. 2 a, b    in a partially open position. In this open position, the pressurized water flows from an inlet pipe  136  of the hydrant  100  into a riser  138  of the hydrant  100 . In contrast to the closed position of the shut-off element  102  shown in  FIGS. 1 a, b   , the difference between the force applied to the underside of the main valve body  106  and the force applied to the top of the main valve body  106  is reduced. In this position, the pressure force or restoring force of the pressure spring  112  is predominant and forces the piston section  114  of the main valve body  106  a piece out of the cylinder chamber  118 . By extending the main valve body  106 , a negative pressure is generated in the cylinder chamber  118 . Due to the negative pressure, the fluid  130  is sucked from the fluid reservoir  122  via the inflow pipe  126  and the check valve  132  into the cylinder chamber  118 . 
       FIGS. 3 a, b    show the shut-off element  102  in a fully open position. In this position, the piston section  114  of the main valve body  106  is fully or maximally extended out of the cylinder chamber  118 , and the cylinder chamber  118  is maximally filled with fluid. The fluid level in the fluid reservoir  122 , however, is lowered compared to the previous positions. 
       FIGS. 4 a, b    illustrate the transition between the open position shown in  FIGS. 3 a, b    and the close position of the shut-off element  102  shown in  FIGS. 1 a, b   . In the  FIGS. 4 a, b   , the shut-off element  102  is not yet completely closed. In this position, water flows under high pressure and with a particularly high speed from the inlet pipe  136  into the riser  138 . Compared to the positions of the main valve body  106  shown in  FIGS. 2 a, b    and  3   a, b , the pressure which acts on the underside of the main valve body  106  is much higher than the pressure which acts on the top of the main valve body  106 . In other words, the difference between the force applied to the underside of the main valve body  106  and the force applied to the top of the main valve body  106  is much greater than the force difference in those positions of the main valve body  106  shown in  FIGS. 2 a, b    and  3   a, b . As a result, the pressure spring  112  is compressed and the piston section  114  of the main valve body  106  moves back into the cylinder chamber  118   a.    
     As explained above, the fluid  130  located in the cylinder chamber  118  thereby flows back into the fluid reservoir  122  via the return pipe  128  at a reduced flow rate. Due to the damping explained above, the main valve body  106  closes at a reduced speed with the sealing surface  108  of the hydrant  100 . Thus, pressure surges are advantageously avoided or at least greatly reduced in their amplitude. Thereby, an advantage is that the main valve body  106  retracts at a speed which is independent of the axial upward movement of the valve rod  104 . In other words, the shut-off element  102  closes at a reduced speed even when the shut-off element  102  is closed at a speed which would have produced a very high amplitude pressure surge without the interposed damping system  110 . 
     To adjust the flow rate at which the fluid  130  flows into the fluid chamber  122 , the length at which the pin  135  retracts into the return pipe  128  may be changed. For this purpose, as illustrated in the embodiment, a pin head  140  of the pin  135  is provided with an external thread at its periphery, which external thread is threadedly engaged with an internal thread of an extension section  142  of the return pipe  128 . The pin head  140  is provided with a slot into which the tip of a screwdriver (not shown) can be inserted. By turning the screwdriver, the pin  135  can thus be further retracted or extended into the return pipe  128 . 
     The return pipe  128  and the extension section  142  of the return pipe  128  are sealed fluid-tight from each other by a second annular seal  144 . Thus, no fluid  130  flows from the return pipe  128  into the extension section  142 . The extension section  142  is sealed in a fluid-tight manner. There is preferably provided an annular guide  146  which also threadably engages the internal thread of the extension section  142 . For this purpose, an outer circumference of the annular guide  146  is provided with an external thread. The annular guide  146  includes an axial bore through which the pin  135  is pushed through without clearance. As a result, the pin  135  is reliably guided axially. The annular guide  146  can be screwed into the extension section  142  until the annular guide  146  comes into abutment with the second annular seal  144 . Alternatively, the annular guide  146  may be spaced from the second annular seal  144 . Further, a third annular seal  148  is provided, which prevents a direct leakage of the fluid from the annular gap  133  via a possible existing gap between a portion of a housing  156  of the damping system  110  and the outer circumference of the pipe body  124 . During extension and retraction of the piston section  114  of the main valve body  106 , the outer circumference of the pipe body  124  thus sealingly glides along the third annular seal  148  in a sealing manner. 
     The fluid reservoir  122  is preferably closed by a cap  150 , which fluid-tightly seals the fluid reservoir  122  via a fourth annular seal  152 . Although not shown, the cap  150  can be sealingly attached, e.g. by welding, to a fluid reservoir wall  158  enclosing the fluid reservoir  122 ; in addition, a ventilation/venting can be provided, via which a pressure compensation can be established in an air space in the fluid reservoir  122 , the air space preferably provided above the fluid  130 , and the outside environment. 
     In the open position of the shut-off element  102 , the pressure difference between the pressure acting on the underside of the main valve body  106  (a pressure from the inlet pipe) and the pressure acting on the top of the main valve body  106  (a pressure from the riser), is reduced. By the reduction of the difference of the forces resulting therethrough, which forces are applied to the underside and top of the main valve body  106  in each case, the pressure spring  112  of the damping system  110  can relax and thus further moved forward or pushed with the main valve body  106  in relation to the valve rod  104 . 
     When closing the shut-off element  102 , the above-mentioned pressure difference and the above-mentioned force difference increase and outweigh the clamping force of the pressure spring  112 . In other words, the pressure spring  112  is compressed again. However, the damping system  110  allows the compression spring  112  to be damped or compressed at a reduced rate. In the above-mentioned valve adjustment, the fluid  130  located in the cylinder chamber  118  of the damping system  110  is transferred again into the fluid reservoir  122  at a reduced flow rate. 
     As shown in  FIGS. 1 a  to 4 b   , the damping system  110  is interposed between the main valve body  106  and the valve rod  104 . Alternatively, the damping system  110  may be interposed in a section of the valve rod  104 . Still alternatively, the damping system  110  may be interposed between an actuator of the valve rod  104  and the valve rod  104 . Further alternatively, the damping system can be interposed in the actuating element itself. It is essential here that the main valve body  106  is coupled axially damped to the valve rod  104  by means of the damping system  110  along the hydrant axis A-A. 
       FIGS. 5 a - d    each show an enlargement view of the damping system  110  in different positions of the shut-off element (see  FIGS. 1 a -4 b   ). Here,  FIG. 5 a    shows the shut-off element in the closed position,  FIG. 5 b    shows the shut-off element in a partially open position, i.e. in a transition between a close position and an open position,  FIG. 5 c    shows the shut-off element in the open position, and  FIG. 5 d    shows the shut-off element in the position shortly before the closed position.  FIGS. 5 a - d    thus show processes in the damping system  110  in a sequence from the closed position via the open position and back to a position shortly before the closure of the shut-off element. 
     The damping system  110  of the shut-off element shown in  FIG. 5 a    in the closed position is an enlargement view of the shut-off elements shown in  FIGS. 1 a, b   . In the following explanation, therefore, reference is made to  FIGS. 1 a, b   . In this position, the main valve body  106  is completely retracted and is in sealing engagement with the sealing surface of the hydrant. 
     The damping system  110  of the shut-off element shown in  FIG. 5 b    in the partially open position is an enlargement of the shut-off element shown in  FIGS. 2 a, b   . In the following explanation, reference is therefore made to  FIGS. 2 a, b   . In this position, the main valve body  106  is pressurized from its bottom as well as its top. The pressure difference between the pressure at the bottom and the pressure at the top decreases with increasing downward movement of the main valve body  106 . Therefore, the restoring force of the pressure spring  112  is stronger, whereby the piston section  114  of the main valve body  106  is extended a piece far out of the cylinder chamber  118 , as indicated in  FIG. 5 b    by an arrow along the extension direction X 1 . This creates a negative pressure in the cylinder chamber  118 . By this negative pressure, fluid  130  is sucked from the fluid reservoir. The fluid  130  flows from the fluid reservoir via the inflow pipe  126  and the check valve  132  into the cylinder chamber  118 . The check valve  132  allows only the inflow of the fluid  130  into the cylinder chamber  118 , but not in the reverse direction. A first flow path in this direction is schematically indicated by P 1  in  FIG. 5 b   . The fluid  130  flows along this first flow path P 1  substantially uninhibited, whereby the downward movement of the main valve body  106  is relatively quickly. Thus, when opening the hydrant at the outlet thereof, the full water pressure is applied without delay. 
     The damping system  110  of the shut-off element shown in  FIG. 5 c    is an enlargement view of the shut-off element shown in  FIGS. 3 a, b    in the fully open position. In this position, the piston section  114  of the main valve body  106  is maximally extended from the cylinder chamber  118 . The cylinder chamber  118  is maximally filled with fluid  130 . 
       FIG. 5 d    shows the damping system  110  of the shut-off element in a position in which the main valve body  106  is almost closed. This Fig. is an enlarged view of the shut-off element shown in  FIGS. 4 a, b   . In the following explanation, reference is therefore made to  FIGS. 4 a, b   . In the illustrated position of the main valve body  106 , the afore-mentioned pressure difference increases with increasing upward movement of the main valve body  106  when closing the hydrant. The resulting force outweighs the pressure force of the pressure spring  112 . Thereby, the main valve body  106  is moved upward, as shown by an arrow along the retraction direction X 2 , and the pressure spring  112  is compressed. 
     In order for the piston section  114  of the main valve body  106  to be able to move upwards in the cylinder chamber  118 , the fluid  130  located in the cylinder chamber  118  must be expelled. For this purpose, a second flow path P 2  is provided, which is separated from the first flow path P 1 . The fluid  130  flows back through the second flow path P 2  from the cylinder chamber  118  back into the fluid reservoir. Thereby, the fluid flows over the annular gap  133 , which is formed between an inner surface of a housing portion of the damping system  110  and an outer surface of the pipe body  124 . This annular gap  133  advantageously serves simultaneously for receiving the pressure spring  112 . From the annular gap  133 , the fluid  130  then flows via the opening  134  into the return flow pipe  128 . Fluid  130  flows upwardly through return pipe  128  into the fluid reservoir. The fluid  130  can only flow into the fluid reservoir via the second flow path P 2 , since the check valve  132  blocks a return flow via the first flow path P 1 . 
     In the return pipe  128 , the pin  135  is at least partially inserted. In this case, the outside diameter of the pin  135  and the inside diameter of the return pipe  128  are dimensioned in relation to one another such that the predetermined annular space  154  or flow-through cross-sectional area is set between the pin  135  and the return pipe  128 . The fluid  130  must thus force itself through this annular space  154  in the axial direction along the pin  134 . As a result, the flow velocity of the fluid  130  is reduced, with the result that the fluid  130  can flow out of the cylinder chamber  118  only slowly. Thus, the piston section  114  of the main valve body  106  is retracted only slowly or damped in the cylinder chamber  118 . As a result, the main valve body  106  is moved only slowly or damped upwards shortly before the closing position of the hydrant, whereby pressure surges are avoided or at least greatly dampened. 
     As described above, the speed at which the main valve body  106  moves upward can be set. For this purpose, the annular space  154  formed in the return pipe  128  can be set by appropriate selection of the outside diameter of the pin  135  and/or the inside diameter of the return pipe  128 . In the embodiment shown in the figures, the distance at which the pin  135  enters the return pipe  128  is adjustable. Thus, the distance along which the fluid  130  must squeeze through the annular space  154  can be adjusted. With increasing length of the distance of the annular space  154 , the return flow of the fluid  130  from the cylinder chamber  118  into the fluid reservoir is delayed. To set the distance of the annular space  154 , the pin  135  is adjustable via a thread. Details of this are described in this description with reference to  FIGS. 1 a -4 d   . Thus, advantageously, the speed at which the hydrant completely closes can be adjusted, essentially independently of the speed by which the operator closes the hydrant. Thus, pressure surges are eliminated or at least greatly attenuated in their amplitude. 
     Like reference numerals refer to the same or corresponding features of the shut-off element and hydrant according to the invention, although is not pointed out in detail in each case and with respect to each figure. 
     
       
         
           
               
             
               
                   
               
               
                 LIST OF REFERENCE NUMBERS 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 A-A 
                 hydrant axis 
               
               
                   
                 P1 
                 first flow path 
               
               
                   
                 P2 
                 second flow path 
               
               
                   
                 X1 
                 extension direction 
               
               
                   
                 X2 
                 retraction 
               
               
                   
                 100 
                 hydrant 
               
               
                   
                 102 
                 shut-off element 
               
               
                   
                 104 
                 valve rod 
               
               
                   
                 106 
                 main valve body 
               
               
                   
                 108 
                 sealing surface of the hydrant 
               
               
                   
                 110 
                 damping system 
               
               
                   
                 112 
                 pressure spring 
               
               
                   
                 114 
                 piston section of the main valve body 
               
               
                   
                 116 
                 fastening element 
               
               
                   
                 118 
                 cylinder chamber 
               
               
                   
                 120 
                 annular seal 
               
               
                   
                 122 
                 fluid reservoir 
               
               
                   
                 124 
                 pipe body 
               
               
                   
                 126 
                 inflow pipe 
               
               
                   
                 128 
                 return pipe 
               
               
                   
                 130 
                 fluid 
               
               
                   
                 132 
                 check valve 
               
               
                   
                 133 
                 annular gap 
               
               
                   
                 134 
                 opening 
               
               
                   
                 135 
                 pin 
               
               
                   
                 136 
                 inlet pipe 
               
               
                   
                 138 
                 riser 
               
               
                   
                 140 
                 pin head 
               
               
                   
                 142 
                 extension section 
               
               
                   
                 144 
                 second annular seal 
               
               
                   
                 146 
                 annular guide 
               
               
                   
                 148 
                 third annular seal 
               
               
                   
                 150 
                 cap 
               
               
                   
                 152 
                 fourth annular seal 
               
               
                   
                 154 
                 annular space 
               
               
                   
                 156 
                 housing of 110 
               
               
                   
                 158 
                 fluid storage wall