TM 10-6640-238-13 1-23 A purge cycle can be initiated in two ways; by the application of external power after a power shutdown or by an alarm signal from the gas detector system. When external power is first applied at connector J1, the power required for a purge cycle is supplied ahead of the Main Circuit Breaker A1CB1.  A1CB1 is held open by power control relay A1K1.  This prevents power from being applied to any equipment or lighting in the Petroleum Laboratory until the purge cycle is completed.  Relay A1K1 supplies power to start the 5-minute time delay relay A3K1 and to energize the two blower control relays (A3K2 and A3K5) which provide power to the ECU blowers.  Power is also routed to the purge door damper motors and to the ventilation damper motors so that the purge door dampers are opened and the ventilation dampers are closed.  The ECU blowers move outside air into the ECU ducting creating pressure which forces any gases or contaminated air outside via the purge exhaust doors.  After 5 minutes have elapsed, time delay relay A3K1 de-energizes.  This causes power control relay A1K1 to de-energize relays A3K2 and A3K5.  Power is removed from the ECU blowers, the dampers are driven to their normal positions and the Main Circuit Breaker may now be closed to supply normal power to the Petroleum Laboratory.  If at the end of the purge cycle the gas detector alarm system is in an alarm condition, the time delay relay is activated causing the cycle to be repeated. This will continue until the alarm clears.  If when power is applied at connector J1 and a purge cycle initiated, and one of the external purge doors is closed, the purge alarm buzzer will be activated by the purge door limit switch and will remain activated until the door is opened. c. Water System  (Refer to Figure 1-7).  The water system consists of the water pump, pressure switch, water tank, water surge tank, filter, water chiller, water heater and associated piping and valves.  The water pump operates on 110V, 60 Hz, single-phase power supplied by A15CB8 located in POWER PANEL NO. 2 and is controlled by the pressure switch.  The water pump turns on when a water outlet is opened and off when the outlets are all closed.  The water surge tank removes oscillations from the system while the water tank acts as the system supply source.  The water cooler operates on 110V, 60 Hz, single-phase power supplied by A15CB7 located in POWER PANEL NO. 2.  The water heater operates on 110V, 60 Hz, single-phase power supplied by A1CB17 located in MAIN POWER PANEL A1.  The system may be supplied with water from an outside pressurized source, from an outside unpressurized source, by using the system pump, or by its own water tank.  Water supply piping and valves are color coded blue.  Water return piping and valves are color coded white.  Drain piping is colored black.  Water supply valves are located at the distillation unit, the RVP Bath, the JFTOT, the sink (both hot and cold), the freezer, the laboratory ovens, the viscosity baths, and the fume hood.  Water return valves are located at the freezer, the laboratory ovens, the viscosity baths, and the fume hood. d. Air System (Refer to Figure 1-7).  The air system consists of the air compressor, air tank, pressure switch, moisture trap, and associated piping and valves.  The air compressor, located in the mechanical room, operates on 208V, 60Hz, 3-phase power supplied from A15CB6 located in POWER PANEL NO. 2 and can supply air at 120 psi to the system.  In automatic operation, the compressor is controlled by a pressure switch which shuts it off when the pressure has reached 120 psi and turns it back on when the pressure in the system drops to 60 psi. The air tank relief valve is set to operate at 150 psi.  Air piping is color coded green and valves are color coded orange.  Air supply valves are located next to the distillation unit, behind the viscosity baths, above the centrifuge, in the fume hood, at the manometer, the bomb manifold, and the gauge test fitting. e. Vacuum System (Refer to Figure 1-7).  The vacuum system consists of the vacuum pump and associated piping and valves.  The vacuum pump is located in the mechanical room and operates on 110V, 60Hz, single-phase power supplied from A15CB9 located in POWER PANEL NO. 2.  It has a free air capacity of 58 liters per minute and supplies vacuum where required.  Vacuum piping and valves are color coded yellow.  Vacuum supply valves are located behind the viscosity baths, above the centrifuge, and in the fume hood. f. Water Still.  The water still is electrically operated and supplies pure water for use in the laboratory.  Located on the curbside wall it operates on 110V, 60Hz, single-phase power supplied from a convenience outlet.