Abrasivejet cutting head with back-flow prevention valve

For use in an abrasivejet cutting system of the type including

• (a) a cutting head disposed about a first generally longitudinal axis and having an upstream end region, a downstream end region, and a longitudinally-extending fluid passageway in fluid communication with said end regions, said upstream region being adapted for coupling to a source of high pressure fluid, said downstream region being adapted to releasably secure an abrasivejet nozzle to hold said nozzle adjacent a workpiece,
• said cutting head including orifice-defining means positioned within the fluid passageway to receive high pressure fluid from the upstream end region and create a fluidjet flowing from said orifice towards the downstream end region in substantial co-axial alignment with said fluid passageway, said fluidjet inducing a generally co-extensive region of low pressure
• said cutting head additionally including abrasive passageway means for conducting abrasive into the fluid passageway downstream of the orifice-defining member to entrain said abrasive in the fluidjet;
• and
• (b) an abrasive hopper for holding a quantity of abrasive material to be conducted to the cutting head;
• a valve assembly for preventing the backflow of fluid and abrasive from said cutting head to the hopper comprising:
• a valve body disposed about a second generally longitudinal axis, said valve body having an upstream end, a downstream end and a generally longitudinally-extending abrasive passageway in fluid communication with its upstream and downstream ends;
• first abrasive conduit means for conducting abrasive from the hopper into the upstream end of the abrasive passageway,
• second conduit means for conducting abrasive from the downstream end of said abrasive passageway into the abrasive passageway means of the cutting head,
• the valve body including a discharge passage formed about a discharge axis that extends obliquely to said second longitudinal axis from the upstream direction into the valve body's abrasive passageway, the valve body having a discharge port at the upstream end of the discharge passageway,
• a freely movable body member positioned within the discharge passage, said body member being of appropriate size, weight and material to be pulled by the low pressure created by the fluidjet into sealing engagement with the valve body to substantially seal the discharge passage from the valve body's abrasive passageway, and to attain a non-sealing position when contacted by backflowing abrasive and fluid moving from the downstream end of the valve body towards the upstream end of the valve body, whereby backflowing abrasive and fluid is conducted by the valve's discharge passageway to the discharge port for discharge from the valve body.