🔍 Key Concepts

• compressor unloading and what it means for starting torque on the prime mover • difference between controlling pressure in the system versus reducing actual compression work in the cylinders • how clearance volume affects compressor capacity and power needed

💭 Think About

• Ask yourself: which option actually prevents the compressor from doing much compression work during start-up, rather than just giving the air somewhere to go? • Think about multi-stage versus single-stage compressors: which choice only applies to certain designs, and which could be a built-in method of reducing load? • Consider how changing the effective compression space (clearance) in a cylinder will change the volume of air taken in and compressed each stroke.

✅ Before You Answer

• Be clear on the definition of "unloaded" for a compressor: almost no compression work and low starting torque, not just low discharge pressure. • Check which options would still require the motor to compress air each stroke, even if the air is then vented or sent somewhere else. • Verify in your mind how an enlarged clearance space changes volumetric efficiency and therefore the load on the compressor.