Product Manual

MASTERLINE SERIES CAP200
Page 27 of 46 REV H JUNE 2017
START-UP
If the compressor is equipped with an automatic start-stop control (with pressure switch
unloading), it is automatically unloaded upon starting, and will automatically load after attaining
running speed. Simply throw the power switch to start the unit.
For engine driven compressors equipped with a pilot valve, the pilot valve must be manually
unloaded prior to starting the compressor.
OPERATING MODES
Automatic Start-Stop (ASSD) with Bleeder-Type Pressure Switch Operation
A compressor equipped for start-stop operation with a bleeder type pressure switch to provide
an automatic unloaded start. When the compressor reaches a predetermined cutoff pressure,
the pressure switch contacts open terminating power to the starter coil and open the exhaust
port on the pressure switch. Discharge line pressure is then vented to atmosphere. When the
cut-in pressure is reached, the pressure switch contacts close completing the control circuit
and starting the motor. The electric motor must be started no more than six (6) times per hour
to provide adequate motor life.
Automatic Start-Stop (ASSD) with Solenoid Valve Piloted Suction Valve Unloading
A compressor equipped for ASSD with solenoid valve controls utilizes air pressure unloaders
(APU). To provide automatic start-stop operation with an unloaded start on these models, a 3-
way solenoid valve with a restricted exhaust and a non-bleeder pressure switch are used to
achieve the following sequence of operation. If the compressor shuts down or stops because
the pressure switch opens, the solenoid valve is de-energized permitting air pressure from the
receiver to act on the unloaders. This unloads the compressor, opening the intake valves,
venting the cylinders to atomosphere.
When the compressor is started again or the pressure switch closes, the solenoid valve is
energized which permits air from the unloader to exhaust through the restrictor plug. The
restrictor plug delays the loading action of the compressor until it has reached operating
speed, which reduces torque demand and starting current for the electric motor.
Constant Speed Control
A compressor unit set up to run continuously has an unloading mechanism to stop the
pumping action of the compressor at a predetermined cut-out pressure and start the pumping
action at some lower pre-determined cut-in pressure. This unloading cycle is accomplished by
holding open the suction valves during the unloading cycle. On the C79 compressor, the low
stage suction valve is held open while a by-pass valve unloads the high stage during the
unloaded cycle.
These methods employ air pressure from the receiver to actuate unloader pistons which
actuate the unloading mechanism. Control of the air pressure to and from the unloaders is
accomplished by either an air pressure actuated pilot valve or by a three-way solenoid valve
controlled by a pressure switch. During unloaded operation, the motor only draws 15-25% of
its normal electrical load.