Abstract: A mixing head for two reactive components has a mixing chamber provided with a control plunger enabling recirculation and opening at right angles into a quieting passage which is provided with a control plunger adapted to selectively obstruct the outlet of the mixing chamber into the quieting passage. According to the invention an adjustable abutment is provided for the latter plunger to enable the obstruction to be completely removed during one phase of each cycle of the actuation of the apparatus. This abutment can be an annular piston under the control of fluid pressure.

Abstract: A mixing head for two reactive components forms a mixture in a mixing chamber when a control plunger is retracted, the mixture passing into a channel at right angles to the mixing chamber. A second plunger in the channel is partially retracted so that its free end is positioned in line with the opening to form a partial obstruction around which the mixture is formed. Then the second plunger is retracted to allow clearing of residues, and advanced to drive residues from the channel.