Abstract: A valve whose casing has two coaxial passages and a chamber disposed between the passages and receiving a valving element movable between an open position in which the passages are free to communicate with one another and a closed position in which the passages are fully sealed from each other. The housing is separably connected with a casing for a tubular filter through which the fluid entering via one of the passages flows on its way toward the other passage when the valving element is held in the open position. The casing can be detached from the housing only when the valving element is held in the closed position to thus prevent leakage or spillage of fluid from the housing on detachment of the casing. The valving element can include a rotary body or a membrane and a displacing member which latter is reciprocable in the chamber to move the membrane against an annular seat of the housing.