introduced cleaning solution r from the leakage chamber 5 is done here by a non specified connection line which is arranged in a tubular extension leading through the first valve housing part 1 a and out of it on the first closing element 3 the removal of an u201c internally u201d introduced cleaning solution by the particular seat cleaning stream r 1 r 2 from the internal chamber 5 which is introduced from the valve housing part 1 a or 1 b assigned at any one time during the seat cleaning of the first or the second closing element 3 4 also see for this fig4 and 5 is done in the same manner as with the external cleaning introduction r in the seat cleaning of the first closing element 3 this is pushed so far in the direction of the second closing element 4 fig4 that a first partially open position t 1 consequently occurs in which the first seat seal 8 has left the assigned first seat surface 2 a gapwise and a first seat cleaning stream r 1 from the first valve housing member 1 a is generated over the exposed first seat surface 2 a in the leakage chamber 5 for seat cleaning of the second closing element 4 this is pushed so far in the direction of the second valve housing member 1 b fig5 that in a thus partially open position t 2 taken from.