as shown in fig1 and 2 , the valve device according to the preferred embodiment of the invention comprises an exterior section 1 and an interior section 2 . arranged in the exterior section 1 are a discharge opening 20 , an actuating mechanism 50 , as well as a connecting channel 30 with exterior connecting channel sections 31 - 33 . arranged in the interior section 2 are an inflow opening 10 , a main valve 40 , as well as lower connecting channel sections 34 - 36 of the connecting channel 30 . in the installed position , the interior section 2 is arranged in a wall or interior of a building while the exterior section 1 is arranged outside of the wall in the exterior where it is exposed to ambient temperatures . in the installed position , the discharge opening 20 faces downward along the direction of gravity . fig2 shows the valve device with its main valve 40 closed . the main valve 40 comprises a first valve element 41 , which is embodied as ceramic disk and possesses two eccentric bores 41 a , b . the main valve 40 also comprises a second valve element 42 , with a cross section in the shape of two triangles , which are in contact by their points and are shaped as semicircles on the sides opposite to these points . the triangular surfaces of the second valve element 42 form two valve sealing faces 42 a , b , which are dimensioned so that they can seal first and second openings in the first valve element 41 . in its closed position , the main valve 40 prevents water from the inflow opening 10 from reaching the connecting channel 30 , by rotating the first valve element 41 relative to the second valve element 42 in such a manner that the two eccentric bores 41 a , b come to rest upon the two valve sealing faces 42 a , b of the second valve element and are sealed by them . turning the first valve element 41 by 90 ° with respect to the longitudinal axis of the valve device causes the two eccentric bores 41 a , b to become aligned with two corresponding openings in the second valve element 42 , so that water can flow from the inflow opening , through the valve device , to the discharge opening . for this , the water enters the valve device in the horizontal direction via the inflow opening 10 . it then passes a check valve 80 arranged downstream of the inflow opening . the check valve 80 comprises a valve seat 81 , into which a valve body 82 is pressed by means of a pressure spring 83 . the water pressure exerts a force counteracting the pressure spring 83 upon the valve body surface 84 and thus lifts the valve body 82 from the valve seat 81 , which allows the inflow of water . the water then flows in the direction of the main valve 40 as indicated by arrow b . the second valve element 42 is connected rotationally rigidly to a coupling element 51 , which in turn is connected rotationally rigidly by means of a key and slot connection to a first end of a short actuating rod 52 . at its other end , the short actuating rod 52 is hexagonal in cross - section and is connected rotationally rigidly by means of a hexagon socket sleeve 53 to a long actuating rod 54 , which also possess a hexagonal cross - section . at its other end , the long actuating rod is attached , by means of an adapter element 55 , rotationally rigidly but axially moveably to a valve sleeve 56 , which in turn is connected rotationally rigidly to an actuating knob 57 . in this way , a torque applied to the actuating knob 57 can be transferred to the second valve element 42 , in order to rotate the second valve element 42 accordingly and to move the main valve 40 from the closed operating position to the open operating position , and in reverse . the actuating knob 57 together with the valve sleeve 56 is axially movable relative to the remaining components of the valve device . the valve sleeve 56 is secured against being pulled out of the valve device in the direction of the actuating knob by a sleeve nut 58 with an outside thread , which is screwed into a corresponding inside thread in a wall section 122 of the housing of the valve device . the main valve 40 is arranged in a pipe section 35 , which is screwed to a pipe section 33 , 34 . the short and long actuating rods 52 , 54 extend through the pipe section 33 , 34 and connect the main valve 40 to the actuating knob 57 situated at a pipe end . the pipe section 35 and the pipe section 33 , 34 are connected to each other by means of an adapter sleeve 60 , by screwing the pipe sections 35 and 33 , 34 with their respective inside threads onto a corresponding outside thread of the adapter sleeve 60 . the adapter sleeve 60 interacts with a stop piece 61 , which is pushed rotationally rigidly onto the hexagonal section of the short actuating rod 52 by means of a hexagon socket , and which comprises two arms 61 a , b extending radially . the arms 61 a , b interact with end stops 62 and 63 of the adapter sleeve 60 and in this manner limit the rotating angle of the short actuating rod 52 , and consequently of the entire actuating mechanism , to 90 °. the stop element 61 is oriented relative to the second valve element 42 in such a way so that — together with a corresponding orientation of the adapter sleeve 60 relative to the first valve element 41 — the main valve 40 is closed in the end stop position shown in fig1 and 2 and is open in the other end stop position reachable by rotating the actuating rod by 90 °. arranged between the actuating knob 57 and the pipe section 32 is a ventilation valve 70 that serves in ventilating the interior of the valve device . the design and function of the ventilation valve 70 will be described with the help of fig3 and 4 . the ventilation valve 70 comprises a valve seat 71 and a valve body 72 . the valve body 72 is integrally formed with the valve sleeve 56 . the valve seat 71 of the ventilation valve 70 is formed in the adapter element 55 , which is inserted in the housing wall of the valve device and sealed by means of two o - rings . the adapter element 55 contains bores 75 , 76 , which provide fluid communication between the ventilation valve 70 and the connecting channel section 32 . a ventilation space 100 is situated between actuating knob 57 and the ventilation valve 70 and is sealed near the actuating knob by means of two o - rings 101 , 102 . a bypass channel 110 leads from the ventilation space 100 diagonally downward into the connecting channel section 31 in proximity of the discharge opening 20 . in this way , air can flow from the connecting channel section 31 to the connecting channel section 32 via a continuous bypass line , formed by the bypass channel 110 , the ventilation space 100 , and the bores 75 , 76 . a pressure spring 73 is supported on an annular shoulder of the housing wall and presses the valve sleeve 56 and the valve body 72 , including the actuating knob 57 fastened thereto , outward . as illustrated in fig1 , a radially arranged guide pin 120 is attached to the valve sleeve 56 and is guided in a guide - pin track 121 in a fixed wall section 122 of the valve device . the guide - pin track 121 allows the actuating knob 57 , with the valve sleeve attached thereto , to be moved axially inward from a starting position , in which the main valve 40 is closed and the ventilation valve 70 is enabled , in the direction of the ventilation valve 70 , whereby it forces the ventilation valve 70 to close by means of contact faces . when the ventilation valve 70 is in its closed position , the guide - pin track 121 allows the actuating knob 57 to be rotated by 90 °. this rotation is transferred via the valve sleeve 56 to the adapter element 55 and further via the actuating rods 54 , 52 to the valve body 42 , which consequently is rotated into its open position . when the actuating knob is rotated back by 90 °, the spring element 73 automatically pushes the actuating knob and the valve body 72 back outward into the starting position . thus , this allows water to drain from the interior of the valve device , since air can penetrate from the discharge opening 20 into the upper region of the valve device via the bypass line , which at the same time allows the residual water to drain from the valve device through the discharge opening 20 . however , if some pressure remains in the valve device , for example as a result of pressure in a connected hose , then this internal pressure will also be applied in the ventilation space 100 via the bypass line . consequently , ventilation of the interior of the valve device does not take place , nor is it possible for liquid to penetrate to the exterior via the ventilation valve 70 , if there is remaining internal pressure with the main valve 40 closed . this reliably prevents liquid from being discharged unintentionally through the ventilation valve 70 . fig5 shows a valve device according to a second embodiment of the invention . this embodiment does not contain a ventilation valve and thus foregoes a forced opening by axial displacement ( in particular pushing ) of the actuating button . the variant of the valve device illustrated in fig5 also exhibits a actuating knob 157 , which is connected rotationally rigid to a long actuating rod 154 via an adapter element 155 . the adapter element 155 contains ventilation channels 175 - 177 , which connect a bypass channel 210 , extending from the proximity of a discharge opening 120 diagonally upward to a ventilation space 200 , to a channel section above the orifice of the bypass channel 210 . this ensures a permanently open connection between the lower channel section 131 and the upper channel section 132 via the bypass channel 210 , the ventilation space 200 , and the ventilation channels 175 - 177 , guaranteeing a reliable ventilation of the interior of the valve device when the actuating knob 157 is moved from the open position to the closed position . the actuating knob 157 in the embodiment shown in fig5 is not axially movable but only can be rotated by an angle of 90 ° about the longitudinal axis of the exterior - wall valve . a connecting - link guide for control of the actuating knob 157 is no longer required in the embodiment shown in fig5 .