starting relay 218 includes normally open contacts 218a in a holding circuit 220 around the starting switch 216 to maintain energization of the starting relay 218 it will be appreciated that the starting relay 218 also closes the circuit to the main blower and conditions the burner for operation which will start as soon as the appropriate vacuum has been developed by the main blower again however these aspects of the operation are old and description is believed unnecessary line 212 is also connected to line 208 by line 224 which includes the normally open mercury switch 148 and a relay 226 the mercury switch 148 has a holding circuit 228 thereabout with normally open relay 226 actuated contacts 226a therein a terminal 230 is situated in line 214 between the starting switch 216 and the relay 218 and a line 232 extends to terminal 234 and has normally open relay 226 actuated contacts 226b therein from terminal 234 a line 236 extends to line 208 and includes a timer 238 a relay 240 and a winding 242 on one side of a pneumatic directional control valve 244 the timer 238 is of the type which when energized conducts for the desired time period and then opens the circuit terminal 234 is also connected to line 208 by a line 246 which includes normally closed solenoid 240 operated contacts 240a and the opposite winding 248 of pneumatic valve 244 the operation of the circuitry is as follows prior to starting a cycle of drying operation the.