PURPOSE: To improve the sealing performance of a frame body and a valve cover by installing in such a way that the tip of a key hole closing valve cover rotatably journalled to the back face does not interfere with the frame body at the rotating time, and mounting packing on a valve seat.
CONSTITUTION: It is so constituted that the tip of the valve seat 10 of a valve cover 1a rotated around a pivot 1b at the lower face of a cover body (a) so as to close the key hole 2 of the cover body (a) is positioned lower than a horizontal line L passing the center point of the pivot 1b and that the end part of the valve cover 1a does not interfere with a frame body (b). Packing 12 is mounted on the valve seat 10 in the state of being held by a keep plate 11, and a valve body 1 provided with a weight 1c is energized by a coil spring 3 so that the engaging piece 1d of the valve body 1 is locked to the engaging piece b' of the frame body (b) even in the case of the frame body (b) being buried in the inclined land. At the time of opening the cover body (a), a hook bar is inserted in the key hole 2 to rotate the valve body 1 against the force of the spring 3, and the tip part 1a' of the valve cover 1a is rotated gradually away from the inner wall of the frame body (b). The sealing performance of the cover can be thereby improved.
KUMAKIRI NOBORU
SUGIMORI KOJI
