Modern chapt 19/20 Review questions Flashcards
which of the following best describes a direct-drive compressor?
a) a compressor connected to a drive motor by a belt and pulley system
b) a compressor and drive motor sharing a single shaft and mounted together in a single housing
c) a compressors crankshaft connected to a motors drive shaft by a coupling
d) a compressor with no crankshaft because each piston is directly waged by a separate drive motor
C) a compressors crankshaft is connected to a motors drive shaft by a coupling
Which of the follow statements is NOT true regarding hermetic compressors?
a) the motor is sealed inside the same dome as the compressor
b) these compressors may be connected to different types of evaporators
c) the shaft seal creates a leakproof seal between the shaft and the case
d) the motor is directly connected to the compressor
These compressors may be connected to different types of evaporator
A (n) ________ connects the piston to the crankshaft in a reciprocating compressor?
a) crank throw
b) connecting rod
c) eccentric
d) piston pin
connecting rod
A reciprocating compressor that has a long piston with an elliptical slot in the bottom of the piston skirt and no connecting rod is referee to as an
a) crank throw
b) elliptical design
c) scotch yoke design
d) hermetic design
scotch yoke design
Which of the following statements regarding rotary compressors is not true?
a) rotary compressors have low volumetric efficiency
b) in some rotating vane compressors, the blades are pushed against the cylinder wall by centrifugal force alone
c) the blade on a stationary-blade rotary compressor is mounted in the compressor housing rather than in the rotor
d) all of the above
a) rotary compressors have low volumetric efficiency
Which of the following is a trait of stationary-blade rotary compressor?
a) the blade is mounted on the rotor
b) the blade is pulled into contact with the rotor by centrifugal force
c) the rotor is mounted on an eccentric shaft
d) all of the above
the rotor is mounted on an eccentric shaft
Which of the following statements regarding scroll compressors is NOT true?
a) scroll compressors operate with continuous suction and discharge, resulting in a very smooth compression cycle
b) in a scroll compressor vapour is compressed by a series of pistons that travel in a spiral pattern through a fixed scroll
b)
Which of the following best describes the compression action in a screw compressor?
a) two scrolls rotating in opposite orbits trap and compress vapour in pockets
b) a pair of helical rotors traps and compresses vapour between the lobes in one rotor and the grooves in the other rotor
c) a high speed reversing motor compresses vapour by pushing and pulling a screw-like piston in a helical cylinder
d) two impellers draw vapour in through opposite ends of a cylinder, causing the vapour to compress in the centre of the cylinder
b)
Which of the statements regarding centrifugal compressors is not true?
a) as the speed of a centrifugal compressor increases , its efficiency decreases
b) vapour is drawn from around the outside of the stator and compressed inward towards its centrally located discharge
c) centrifugal compressors often have multiple impellers that operate in series
d) all of the above
as the speed of a centrifugal compressor increases its efficiency decreases
Which of the following statements describes mufflers?
a) a muffler reduces noise that may be caused by gas pulsation
b) a muffler smooths out gas flow
c) a muffler is installed vertically near the compressor
d) all of the above
all of the above
Which of the following is not an approved method of cooling compressors?
a) using cool suction vapour and oil to cool a compressor motor
b) running water through water jackets around a compressors cylinder
c) blowing air across a compressors exterior
d) using a small relief valve to vent refrigerant to the atmosphere for evaporative cooling around the crankcase
using a small relief valve is not acceptable
Which of the following statements about lubricating oils is not true?
a) lubricating oils may include additives
b) lubricating oils may be mineral oils that contain wax
c) lubricating oils have a viscosity that is best for the refrigerant
d) lubricating oils may be mineral oils that are non-foaming
b) lubricating oils may be mineral oils that contain wax
The primary purpose of a crankcase heater is?
a) to minimize changes in bearing tolerances due to thermal contraction
b) to minimize the amount of liquid refrigerant in the compressor oil
c) to superheat suction vapour entering the compressor
d) to prevent oil from freezing in the crankcase
b) to minimize the amount of liquid refrigerant in the compressor oil
- Assuming that the motors are single speed and not equipped with a VFD, explain why most belt-driven compressors turn at a different speed then their motors. How does this happen? How can compressor speed be increased? How can it be decreased?
- If the compressor pulley is larger than the motor pulley the compressor turns slower
- increase = comp pulley smaller than drive motor pulley
- decrease = comp pulley larger than drive motor pulley
List four benefits of scroll compressors over reciprocating compressors
Lighter more efficient less parts continuous process gives compressor smooth action quieter
