A liquid filter having a housing and a hollow insert. The housing has a dirty liquid feed, a clean liquid outlet and a drainage channel, and is closed by a detachable cover. In the channel, a valve is arranged, having a valve body axially displaceable between a closed and an open position. The cover on the housing presses the valve body into the closed position. When the cover is removed from the housing, the valve body is carried to its open position and then is detachable from the cover or insert and is retainable in its open position by a spring holding element. The holding element automatically expands into the opening position by spring force and engages a spring element restraint holding the valve body in its open position. A force contracts the spring element, displacing the valve body in the closing direction, releasing engagement with the spring restraint.