Compressor Types & Operation
Reciprocating, scroll, screw, and rotary compressors including hermetic, semi-hermetic, and open-drive designs.
- Identify reciprocating, scroll, screw, and rotary compressor types
- Distinguish hermetic, semi-hermetic, and open-drive compressor designs
- Calculate compression ratio and understand its effects
- Diagnose valve failure, slugging, and short cycling
- Explain capacity control methods and economizers
Lesson 1
Reciprocating, Scroll & Screw Compressors
Reciprocating Compressors
A reciprocating compressor uses pistons to compress refrigerant vapor. Pistons move back and forth inside cylinders, drawing in low-pressure vapor on the intake stroke and compressing it on the compression stroke. Suction and discharge valves (reed valves) control flow direction.
Reciprocating compressors are the oldest and most common type. They are available in sizes from small fractional-horsepower units to large multi-cylinder industrial models.
Scroll Compressors
Scroll compressors use two spiral-shaped scrolls - one fixed and one orbiting. As the orbiting scroll moves, gas pockets between the scrolls progressively shrink, compressing the vapor. The advantage of a scroll compressor over reciprocating is fewer moving parts, quieter operation, and more efficient performance.
Reciprocating
Mechanism: Pistons in cylinders
Valves: Reed suction and discharge valves
Pros: Wide range of sizes, field serviceable
Cons: More vibration, valve wear
Scroll
Mechanism: Orbiting and fixed scrolls
Valves: No suction or discharge valves
Pros: Fewer parts, quieter, more efficient
Cons: Not field repairable, limited sizes
Screw
Mechanism: Helical rotors (twin or single)
Valves: No valves needed
Pros: Continuous compression, large capacity
Cons: Requires oil management, high cost
Screw Compressors
Screw compressors use interlocking helical rotors that trap and compress gas as it moves from the suction end to the discharge end. They provide continuous, pulse-free compression and are used in medium to large commercial and industrial applications.
Reciprocating compressors use pistons and are the most common type. Scroll compressors have fewer moving parts, are quieter, and more efficient. Screw compressors provide continuous compression for large systems.