Differential pressure metering and dispensing system for abrasive media

In an apparatus for blasting, comprising:

• a pressure vessel means for containing a quantity of particulate abrasive blasting medium;
• a source of pressurized air and means for pressurizing said pressure vessel by providing fluid communication between said pressure vessel and said source of pressurized air;
• means for feeding said blasting medium from said pressure vessel to a media outlet from said feeding means to an air conveying line to form a mixture of blasting medium and pressurized air;
• said air conveying line being in fluid communication with said source of pressurized air and containing a bend upstream of said media outlet, said bend sufficient to result in air separation and back-mixing transversely across said bend and air turbulence downstream of said bend;
• an orifice in said feeding means upstream of said media outlet for restricting the flow of said blasting medium to said air conveying line;
• means for separately controlling the pressure in said pressure vessel and in said conveying line to provide a pressure differential such that the pressure level within said pressure vessel is greater than the pressure within said conveying line;
• and
• means for discharging said mixture of blasting medium and pressurized air through a nozzle at the end of said conveying line, the improvement comprising;
• an air flow straightening means provided in said conveying line upstream of said bend so as to reduce said back-mixing and downstream turbulence.

In a method for blasting, comprising the steps of:

• containing a quantity of blasting medium comprised of fine particles having a mean particle size of from about 50 to 1000 microns within a pressure vessel;
• pressurizing said pressure vessel by providing fluid communication between said pressure vessel and a source of pressurized air;
• feeding said blasting medium from said pressure vessel, through a media discharge line to a media outlet into a conveying line, said conveying line being in fluid communication with said source of pressurized air;
• restricting the flow of said blasting medium to said conveying line at a flow rate of from about 0.5 to 10 pounds per minute through an orifice in said media discharge line and having a predetermined area and which is upstream of said media outlet.
• mixing said blasting medium with the stream of pressurized air flowing within said conveying line;
• controlling the pressure in said pressure vessel and in said conveying line to provide a pressure differential such that the pressure level within said pressure vessel is greater than the pressure within said conveying line;
• regulating said pressure differential in proportion to the flow of blasting medium through said orifice to provide a blasting medium-to-air ratio in the conveying line of between about 0.05 and 0.5 by weight;
• and
• discharging said mixture of blasting medium and said stream of pressurized air through a nozzle at the end of said conveying line, the improvement comprising;
• equalizing the air pressure between the conveying line at a location upstream from said outlet and the media discharge line immediately downstream of said orifice and upstream from said outlet.