Spec Sheet

17
valve directs the fl ow into the air system or to the atmosphere.
Start-Stop Control Units
As with constant run units, the air intake is controlled by air pressure demand. Instead of being
controlled by a pilot valve, Start-Stop units are controllled by an electrical switching device, called a
pressure switch. When the system reaches a designated pressure, or maximum pressure set point,
the pressure switch de-energizes the electric motor. As air is consumed and the system pressure falls
below another designated pressure, or minimum pressure set point, the pressure switch energizes
the electric motor.
Unloading the pressure from the pump for Start-Stop Units is accomplished either by a pressure
switch with unloading capabilities (Single Stage Units) or by a centrifi cal unloader(Two Stage Units).
Centrifi cal Unloader Units - Centrifi cal Unloader units use the rotation of the pump to actuate a
specially designed valve. As the pump rotates, weights spin outward causing a specially designed
valve to close. When the pressure switch de-energizes the electric motor, the pump stops spinning
and consequently allows weights to return to their original position and open the valve. This allows the
trapped air between stage one and two to escape through the valve and bleed to the atmosphere.
Dual Control Units
Dual Control Units allow the compressor to operate in both constant run and start-stop
control. The unit has both a pilot valve and a pressure switch. The unit can be switched from either
operating mode by opening and closing a ball valve. The pilot valve is used to control the compressor
when operating in the constant run and the pressure switch is used to control the compressor when
operating in the stop/start mode.
A good rule of thumb in determining which is the best mode of operation is by the amount of time the
compressor will be required to supply air. If the demand for air is infrequent, then the unit should be
set up for stop/start operation to minimize unnecessary run time and operational wear and tear and to
save energy. If there is a frequent or extended demand for air, and/or the unit is located in a distant or
remote area where access to the compressor is diffi cult, the unit should be set up for constant run to
minimize the number of times the motor must start in an hour to ensure good motor life.
PILOT VALVE
The pilot valve is a pressure control device used to maintain system pressure within a preset
range while the compressor runs contantly. The pilot valve may be used to actuate an unloading
device such as a discharge line unloader or an unloading device in the head of the compressor.
When the system reaches a predetermined pressure, the pilot valve actuates the unloading device
and allows the system to run in the unloaded mode. When the system falls below the preset cut-in
pressure, the pilot valve closes and disengages the unloading device(s) which allows the compressor
to pump air into the system.
PRESSURE SWITCH
The pressure switch is a pressure control device. It functions by opening and closing an
electrical switch based on the system pressure. When the system pressure reached a preset
pressure, the pressure switch opens a set of electrical contacts which in turn shuts off the electric