Compressors & Condensers Flashcards

What does 'volumetric efficiency' describe in a reciprocating compressor?

Answer: The ratio of actual refrigerant mass pumped to the theoretical displacement of the compressor

Volumetric efficiency compares the actual mass of refrigerant moved per stroke to the theoretical maximum based on cylinder displacement, and it decreases at high compression ratios due to reexpansion of clearance gases.

What is an evaporative condenser and what is its primary advantage?

Answer: A condenser that rejects heat by spraying water over coils while air passes over them; it achieves lower condensing temperatures than air-cooled units

An evaporative condenser sprays water over refrigerant coils while a fan draws air through; the evaporation of the water provides much more cooling than dry air alone, allowing lower condensing temperatures and higher system efficiency.

What is 'compressor short cycling' and what are its main causes?

Answer: Rapid and repeated on-off cycling of the compressor; caused by oversized equipment, low refrigerant charge, or faulty controls

Short cycling refers to the compressor turning on and off too frequently, which stresses motors and bearings; common causes include oversized systems that quickly satisfy the setpoint, low refrigerant charge, or faulty pressure controls.

In a semi-hermetic compressor, what maintenance advantage does it offer over a fully hermetic compressor?

Answer: It can be disassembled and repaired in the field, allowing valve replacement and motor rewinding

Semi-hermetic compressors have bolted access covers that allow the technician to access and replace valves, pistons, connecting rods, and even rewind the motor, extending the useful life of the compressor.

What is the purpose of a discharge muffler on a refrigeration compressor?

Answer: To dampen pressure pulsations in the discharge line, reducing vibration and noise

A discharge muffler attenuates the pressure pulsations generated by the reciprocating piston action, reducing vibration, noise, and potential stress on discharge line piping.

What is the role of the unloader on a compressor?

Answer: To reduce compressor capacity by holding suction valves open on selected cylinders so they do not pump

A compressor unloader mechanism holds suction valves open on one or more cylinders so those cylinders do no useful compression work, effectively reducing the compressor's pumping capacity to match lower load conditions.