PNEUMATIC TRANSPORTATION APPARATUS

PURPOSE:To make it possible to automatically release the stagnation of a granular material such as, for example, mold sand, by arranging a secondary air- pipe in parallel with a conveying pipe in a pneumatic conveying pipe line system for granular materials, and by connecting between both pipes with a plurality of communicating pipes incorporated therein with differential pressure valves. CONSTITUTION:A granular material M is conveyed in a conveying pipe 1 by compressed air in the direction of the arrow. Further, high pressure air at a pressure higher than the pressure of air in the conveying pipe 1 is filled in a secondary air-pipe 2. As a result, the pressure in the secondary air-pipe 2 is applied to the inlet side 7 of differential pressure valves 4A-4C, but the flowing-out of the air to the outlet side of the valves are normally interrupted by valve seats 9. Further, pressure in communicating pipes 3A-3C is applied into a diaphragm chambers 10 in the differential pressure valves 4A-4C through pilot pipes 15A-15C. When the granular material M is stagnated in the conveying pipe 1, the differential valve 4B opens for discharging high pressure air from the air-pipe 2 into the conveying pipe 1 through the communicating pipe 3B, and therefore, the flow of the granular material M is interrupted for retrieving the normal transporting condition in the conveying pipe 1.