Pneumatic abrasive cutting apparatus

Claim 1

A CONTROL SYSTEM FOR AN APPARATUS FOR FEEDING A FLOWABLE SUBSTANCE INTO A PRESSURIZED GAS STREAM COMPRISING A CONDUIT HAVING A DELIVERY END AND A SOURCE END, A TANK CONTAINING SAID SUBSTANCE CONNECTED AT A FIRST JUNCTION TO SAID CONDUIT INTERMEDIATELY OF SAID ENDS WHEREBY THE PRESSURE IN THE TANK IS SUBSTANTIALLY EQUAL TO THE PRESSURE OF THE GAS AT SAID JUNCTION, AND A PRESSURE CONTROL MECHANISM CONNECTED AT A SECOND JUNCTION TO SAID CONDUIT, SAID MECHANISM IN A FIRST OPERATING STATE CONNECTING SAID CONDUIT TO EXHAUST AND THEREBY REDUCING PRESSURE AT SAID SECOND JUNCTION WHICH REDUCES PRESSURE AT SAID FIRST JUNCTION BELOW TANK PRESSURE AND CAUSES INJECTION OF SAID SUBSTANCE FROM THE TANK INTO THE CONDUIT AND IN A SECOND OPERATING STATE DISCONNECTING SAID CONDUIT FROM EXHAUST AND THEREBY CAUSING PRESSURE OF THE TANK TO BE SUBSTANTIALLY EQUAL TO THE PRESSURE OF THE GAS AT SAID FIRST JUNCTION, CUTOFF VALVE MEANS CONNECTED TO SAID CONDUIT AT SAID DELIVERY END HAVING FIRST AND SECOND OUTPUT PORTS, SAID FIRST PORT BEING NORMALLY OPEN AND SAID SECOND PORT BEING NORMALLY CLOSED RELATIVE TO SAID SOURCE END OF SAID CONDUIT, AND A PRESSURE SENSITIVE CONTROL VALVE CONNECTED TO SAID NORMALLY CLOSED SECOND PORT AND LOCATED ADJACENT TO SAID PRESSURE CONTROL MECHANISM HAVING CONTROL MEANS, SAID CONTROL MEANS BEING ENGAGEABLE WITH SAID MECHANISM WHEN SAID FIRST PORT IS CLOSED AND SAID SECOND PORT IS OPENED TO FLUID PRESSURE OF SAID SOURCE.