Cabinet door interlock

Claim 1

In a blast-finish cabinet in which the surfaces of articles may be blast-finished by abrasive media carried in a stream of air supplied from a source of air under pressure, the cabinet having a blast chamber provided with at least one opening providing access to the interior of the chamber, said opening being normally closed by a latched access door openable by a user to permit said articles to be inserted in and removed from the cabinet interior through said opening, a blast nozzle within the chamber for directing against the article surface abrasive media carried in said stream of air under pressure, and a primary air line through which the carrier air is supplied under pressure directly from said source to the nozzle, an improved interlock system for shutting off the supply of air to the nozzle whenever the door is inadvertently left unlatched and open, comprising: (a) a normally closed main control valve of the pneumatic, pilot-air-controlled type mounted in the primary line and comprising the sole valve controlling the passage of the carrier air through the primary line; (b) a pilot air tubing system disposed wholly outside the flow path of the carrier air stream passing through the primary line from said source to the nozzle and including (1) a pilot air supply line branching off from and connected in communication with the primary line at a location between said source and the valve; and (2) a pilot air control line in communication with the pilot air supply line and having at least one outlet opening to the ambient atmosphere, the control line having a connection to the main valve effective to operate the valve to open position in the presence of air under pressure within the control line; (c) means on the door adapted to sealably close the outlet opening of the pilot air control line responsive to closing and latching of the door, the outlet opening exhausting to the ambient atmosphere air flowing into the pilot air tubing system from said source when the door is left open, whereby to de-pressurize the pilot air control line and thus prevent operation of the valve from its normally closed condition; and (d) a normally closed secondary valve adapted for operation under the control of an operator and mounted to control flow through the pilot air supply line, said secondary valve being mounted wholly out of the path of the carrier air stream flowing from said source through the primary line to the nozzle.