Lance extension venturi sleeve

In a powder delivery system for spraying powder entrained in an air stream wherein the system includes a powder spray controlling gun, means for conveying an air stream entraining powder from a pump to said gun, a gun barrel integral with said gun and an elongated lance extension having a rear end operatively mounted on said forward end of said gun barrel for conveying powder from said forward end of said barrel of said powder spray gun at a rearward, upstream end of the extension to a spray nozzle spaced from said gun and disposed at a forward, downstream end of the lance extension, said extension comprising an elongated tube having a length of about 6 to about 24 inches and having an inner surface comprising an elongated internal bore of substantially constant diameter defining a path for powder blown by an air stream therethrough in a downstream direction from said gun to said nozzle, and an electrode sleeve extending through said extension and defining with said extension a powder stream flow path having a cross-sectional flow area;

• the improvement comprising:
• venturi means for homogenizing powder within said air stream in said lance extension, said venturi means including;
• an elongated venturi sleeve having upstream and downstream ends and being disposed within the upstream, rearward one-third of said lance extension tube and between forward and rearward ends of said extension;
• an internal bore in said venturi sleeve defining a portion of said path and terminating at a downstream end of said sleeve within said tube;
• a tapered bore in said venturi sleeve coaxial with and operatively communicating with the internal bore in said sleeve, said tapered bore extending from one diameter near said internal venturi sleeve bore to a greater diameter in an upstream direction from said internal sleeve bore;
• said downstream end of said venturi sleeve comprising a flat face in a radial plane, said internal bore of said venturi sleeve terminating at a port in said face radially spaced inward from said inner surface of said extension tube and opening abruptly into said tube;
• said electrode sleeve extending through said internal bore and said tapered bore in said venturi sleeve and defining therewith a powder stream flow path having a cross-sectional flow area through said venturi;
• said venturi means creating increased velocity and turbulence within said path in said lance extension tube when air and powder are blown therethrough, thereby homogenizing powder within said air stream and within said lance extension tube beyond said gun barrel forward end, but upstream of said spray nozzle, and whereby said turbulence is diminished in the downstream two-thirds of said extension tube to provide a homogenized uniform powder and air stream to said nozzle for discharge therefrom in a uniform pattern.