Product Manual

MASTERLINE SERIES CAP200
Page 28 of 46 REV H JUNE 2017
The unloaders are of “O” ring and piston type with pressure and over travel compensating
spring. This in turn contacts the valve which has a built in unloader fork and return spring. To
check to see if unloader is stuck open or closed the action can be viewed on the low-pressure
cylinders by removing air inlet filter and elbow and watching the operation through the inlet
opening.
If the piston unloader becomes sticky or jerky in operation, remove the unloader cylinder and
piston assembly. Remove all dirt or carbon and lubricate the unloader piston and cylinder with
a high temperature bearing grease before re-assembly and installation.
Pilot Valve
The pilot valve supplied with certain compressor units is a spring-loaded ball and seat type.
When air receiver pressure reaches the pre-set (adjustable) cut-out pressure, the ball is
unseated permitting air pressure to actuate the unloaders. When the air receiver pressure
drops to the cut-in pressure, the ball reseats and relieves the pressure acting on the unloaders
permitting the compressor to pump again.
For engine driven compressors these valves have a manual override device consisting of a
cam located at the exposed end of the stem, which forces the stem outward. This permits
manual unloading and reloading of the compressor unit. Should these valves become faulty in
operation, they may require disassembly and cleaning (especially the filter). After reassembly,
the pressure settings (cut-out and cut-in) must be readjusted.
Dual Control Operation: Hand Off Auto (HOA)
Compressors equipped with the HOA Dual Control feature have the option of running in either
Constant Run or Automatic Start Stop depending on air demand. The FS Curtis design utilizes
a three way solenoid valve controlled by a selector switch built directly into the starter. Simply
change the position of the selector switch to adjust the operation of the compressor. The Auto
position stands for Automatic Start Stop, the Hand position stands for Constant Run.
Dual Control Operation: Pilot Valve
Electric compressors with pilot valves do not have an HOA switch but can still be operated in
either start-stop or constant run mode. Turning the knob on top of the pilot valve all the way
clockwise will run the unit in start-stop, operated by the bleeder-type pressure switch. Turning
the knob all the way counterclockwise will run the unit in continuous run, operated by the pilot
valve.