A gas venting arrangement incorporated into a mold for use in a die casting or injection mold machine, having a passage for venting gases including by-pass passages and a valve chamber consisting of a forward portion formed in the mold where the valve is slidably received and a rear portion formed by a member separate from the mold. The valve and the passage are designed so that the valve is forced to move from an opened position to a closed position to shut the passage upon axial impingement of a melt from a cavity of the mold. The arrangement has a first system for biasing the valve into the opened position, a second system for biasing the valve into the opened position upon the melt impingement, and a system for releasing the valve from the second biasing means to return from the opened position to the closed position. There is provided a piston-cylinder device, in which the valve and the rear portion of the valve chamber form the piston and the cylinder, respectively, which device provides the first releasing system when the piston is actuated to move forward and second system for releasing the valve from the first biasing system to move from the closed position to the open position when the piston is actuated to move rearward.