an impingement mixing device is provided comprising a mixing chamber housing , a control piston axially displaceable with said mixing chamber housing between an extended position and a retracted position , a mixing chamber within the housing defined by an end face of the control piston when in the retracted position and a mixing chamber discharge outlet coextensive with an end face of said control piston when in the extended position , means to feed first and second components to the mixing chamber in opposing relationship , a discharge tube housing defining a quieting chamber having an opening at a discharge end and in fluid communication with the mixing chamber , with said discharge tube housing including a sealing means adapted to at least partially close the opening of the quieting chamber at the discharge end .