🔍 Key Concepts

• Operation of an automatic unloader on a reciprocating or rotary air compressor • Difference between start/stop control and capacity control in the 100–110 psi range • How the control line from the receiver feeds back to a device on the compressor or inlet system

💭 Think About

• Look closely at what component in the drawing is connected by the small control line from the receiver when pressure rises above 100 psi. What does that line operate? • Between 100 and 110 psi, is the compressor completely stopped, or is something being gradually restricted or opened to reduce the amount of air actually delivered? • Is the control acting on the compressor speed, the air intake, or dumping compressed air to atmosphere? Which one is shown in the picture?

✅ Before You Answer

• Trace the control pressure line from the receiver to see what part it affects (intake, discharge, or motor). • Confirm whether the motor/compressor appears to run continuously while a valve or unloader modulates flow, or whether there is a clear on/off pressure switch. • Identify if there is a butterfly valve in the intake stream, and whether the drawing shows it partly opening/closing in response to receiver pressure.