High velocity mixing system

A mixing head for a high velocity reaction injection apparatus for mixing and dispensing at least two liquid components, each of the components supplied under pressure from a delivery system including a recirculation line to enable circulation of the respective component when the components are not being mixed, comprising:

• (a) a housing defining a mixing chamber with an inlet for each component and an outlet for dispensing the mixed components;
• (b) means for injecting each component through a different one of the inlets into the mixing chamber including means for directing the component through a flow accelerating passage prior to injection into the mixing chamber, for imparting a pressure drop in the component on the downstream side of the passage, and a recirculation outlet communicating with the downstream side of the passage and adapted to be connected to the respective recirculation line;
• (c) means for selectively blocking each inlet for interrupting the delivery of each component and thereby increasing the pressure of the component in the injection means downstream of the passage;
• and
• (d) means responsive to increased pressure downstream of the passage for directing the flow from the passage through the recirculation outlet when the inlet is blocked and for interrupting the flow through the recirculation outlet when the inlet is open and the component may be injected into the mixing chamber.