Automatic powder feeding apparatus

Claim 1

An automatic powder feeding apparatus including a sensor nozzle (3) for blowing a carrier fluid to convey the powder into an inlet of a detector tubular passageway (1) having an inlet (8) and an outlet (9), a powder introducing means (7) provided between the inlet of said detector tubular passageway and said sensor nozzle, means (26) for detecting a pressure difference between an inlet side pressure detecting port (6) provided upstream of the outlet of said sensor nozzle and an outlet side pressure detecting port provided at the outlet (9) of said detector tubular passageway, means (16¹) for shunting a part of said carrier fluid to said inlet side pressure detecting port (6), means (15,18) for regulating a pressure at the outlet of the detector tubular passageway, means (14) for regulating a pressure at the inlet of the detector tubular passageway, said means for regulating a pressure at the outlet of the tubular passageway being an injector (46) connected via a valve (49) to said outlet of the detector tubular passageway, and an automatic control valve (38) being different from said valve (49) and having said pressure difference applied as its input and a flow rate of a driving fluid (47) of said injector issued as its control output and including means (72,73) for presetting a set value corresponding to said pressure difference; characterised in that said automatic control valve (38) and said output side pressure detecting port (9) are connected to each other via a three-way valve (56) connected so that in normal operation said valve (38) and port (9) are connected together, and a constant pressure source (57) is isolated therefrom, and when the apparatus is stopped said valve (38) communicates with said constant pressure source (57) and said port (9) is isolated therefrom.