Ch 5. Compressors

In which of the following compressor construction arrangements are the motor and compressor enclosed within a permanently sealed housing?

*A) Hermetic* B) Open type C) Semi-hermetic D) Direct coupled

In which compressor design is suction gas compressed between rotating gears (helical lobes), after having entered the compressor through a sliding vane type capacity control valve?

*A) Screw compressor* B) Rotating vane compressor C) Stationary single blade compressor D) Scroll compressor

In a two stage centrifugal compressor with an economizer, in which stage is the refrigerant pressure greatest?

A) 1st stage B) 2nd stage *C) Each stage holds equal volume* D) Varies with operating conditions

In a two stage centrifugal compressor with an economizer, which stage holds the largest volume of vapor?

A) 1st stage B) 2nd stage *C) Each stage holds equal volumes* D) Varies with operating conditions

A two cylinder single acting vertical compressor has a suction pressure of 45 PSIG. The purpose of the shaft seal is to keep:

A) Air from entering B) Air and moisture from entering C) Oil from escaping *D) Refrigerant and oil from escaping*

For a given operating condition and motor horsepower, which of the following compressors will have the smallest displacement?

A) Centrifugal B) Screw *C) Rotary* D) Scroll

Which of the following states one of the functions of a compressor?

A) Compress refrigerant so that it will all fit into the condenser B) Compress liquid refrigerant so that it will vaporize C) Circulate the refrigerant through the condenser tubes *D) Provide the differential pressure needed to circulate the refrigerant through the cycle*

Which of the following is closest to the crankcase pressure of an operating reciprocating compressor?

A) Condensing pressure B) Atmospheric pressure C) Mid-point between evaporator and condenser *D) Evaporator pressure* *Evaporator pressure is also the same as suction pressure and crankcase*

The pressure developed by a centrifugal compressor is determined by:

A) Economizer controls *B) impeller tip speed* C) Position of vane control D) Refrigerant type

Which compressor construction arrangement is characterized by one end of the compressor's shaft extending beyond the compressor housing?

A) Hermetic *B) Open type* C) Serviceable single blade compressor D) Centrifugal

Which of the following best describes the operational characteristics of centrifugal refrigeration machine?

A) High volume, high pressure B) Low volume, low pressure *C) High volume, low pressure* D) Low volume, high pressure

Which of the following best describes how a "positive displacement" compressor increases the pressure of a refrigerant?

A) Increased velocity pressure *B) Volume reduction* C) Increasing the refrigerant's specific gravity D) removal of latent heat

Modern compressors use what type of material at their shaft seals?

A) Lead *B) Copper and packing* C) Low friction plastics D) packing glands

What advantage do semi hermetic compressors have over hermetic compressors?

A) Light weight design B) Less expensive *C) Field serviceable* D) Consume less energy per ton of cooling

Which of the following best describes the state of the refrigerant at the inlet and outlet of the compressor?

A) Low pressure liquid in, low pressure liquid out B) Low pressure vapor in, High pressure liquid out *C) Low pressure vapor in, High pressure vapor out* D) High pressure vapor in, high pressure liquid out

A double acting compressor has which of the following operational characteristics?

A) Produces discharge at one end of the cylinder B) Produces discharge at both end of the cylinder *C) Produces suction and discharge at both ends of the cylinder* D) Produces suction on alternate strokes

What type of compressor valves need the most clearance space when used on vertical compressors?

A) Ribbon B) Ring Plate *C) Poppet* D) Feather

What type of compressor is most likely to be used in a system which is operating in a vacuum?

A) Screw B) Scroll C) Rotary *D) Centrifugal* *Centrifugal compressors operating in a vacuum always use refrigerants R-11 or R-123*

Which of the following compressors uses non-positive (variable) displacement to increase pressure of a refrigerant?

A) Scroll B) Screw *C) Centrifugal* D) Rotary

If a refrigeration system is said to have 3 stages. This implies:

A) Three steps of capacity are obtainable B) The system can cool, heat, or dehumidify *C) The pressure of the refrigerant is increased 3 times before it is discharged to the condenser* D) The unit was factory shipped in 3 parts