Abstract: A leakproof valve has a valve housing which consists of an upper portion and a lower portion each connectable to a conduit. Between these portions there is a communication which has a conical valve seat with two sealing rings of different diameters. Two outer cone parts in a three-way divided valve cone cooperate with the sealing rings of the valve seat for forming double seals betwen the upper and lower portions of the valve housing. The third cone part is located between and movable with respect to the two oute cone parts. On closure of the communication, the third cone part will substantially abut against the seat between the sealing rings such that no cavity is formed here. A subsequent shifting of the third cone part with respect to the two outer cone parts opens a communication from the region between the seals to a bleeder outlet.