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Oil Level Gauge - This gauge is located on the oil reservoir and indicates the oil level. See "Oil Level
Gauge", Figure 5-4, page 30, for how to read oil level.
Minimum Discharge Pressure/Check Valve - An internal spring-loaded minimum pressure valve is used
in the final discharge line to provide a positive pressure on the coolant system of the compressor even if
the air service valve is fully open to atmospheric pressure. This valve also functions as a check valve to
prevent back flow of air from the shop air line when the unit stops, unloads, or is shut down.
The valve incorporates an orifice which, when air is flowing through it, maintains pressure in the oil
reservoir. A spring-loaded piston valve senses air pressure on the upstream (reservoir) side of the valve.
When the system pressure rises, the spring is overridden and the valve opens to full porting.
Inlet Valve (Figure 4-1, page 17) - The Inlet valve restricts the inlet to control delivery and closes to
unload the compressor. At shutdown, the inlet valve closes to prevent the back flow of air.
The inlet valve position is controlled by air pressure in its piston cylinder, which is controlled by the
"AutoSentry" through the magnetic unloader solenoid valve. When the top of the cylinder is pressurized,
the inlet opens for full air delivery. When pressure is relieved from the cylinder, the inlet valve closes to
restrict air flow and compressor delivery.
Magnetic Unloader Solenoid Valve (Figure 4-1, page 17) - This valve controls the position of the inlet
valve in response to signals from the "AutoSentry". When de-energized, pressure is relieved from the top
of the inlet valve cylinder to unload the compressor. When the solenoid valve is energized, reservoir
pressure is supplied to the top of the cylinder to load the compressor.
Check Valve (Figure 4-1, page 17) - This valve is normally closed while the compressor is loaded or
stopped. While running unloaded, it opens to admit a small amount of purge air to the compressor inlet.
This reduces compressor knock, and provides enough air to pressurize the controls during startup.
Blowdown Valve (Figure 4-1, page 17) - The blowdown valve is a two-way solenoid valve which is piped
into the oil reservoir outlet ahead of the minimum pressure valve. When the solenoid is de-energized, the
valve opens and the coolant system is blown down. When the solenoid is energized, the valve closes to
allow the coolant system to pressurize.
System Pressure Transducer (Figure 4-1, page 17) - This transducer is connected after the minimum
pressure valve. It converts the pressure in the plant air system into an electrical signal for use by the
"AutoSentry" controller for modulation and control.
Reservoir Pressure Transducer (Figure 4-1, page 17) - This transducer is connected to the coolant
system. Its signal is used to prevent loaded starts, monitor oil pressure, and to monitor the condition of
the separator.
Air Filter Vacuum Switch (Figure 4-1, page 17) - This switch is used to monitor air filter condition and
alert the user if the filter requires service or replacement.
Machine damage will occur if compressor is repeatedly restarted after any one
of the shutdown modes stops operation of the unit. Find and correct the
malfunction before resuming operation.
Discharge Thermistor (Figure 4-1, page 17) - This sensor is located directly in the compressor
discharge. Its signal is used to monitor compressor temperature and shut down the compressor if a
coolant problem is detected.
CAUTION
13-8-621
Page 19
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