433 Flashcards
A positive displacement compressor uses a piston or other device to
compress refrigerant vapor in a chamber
which of the following is a kind of kinetic displacement compressor
centrifugal
which of the following is part of a scroll compressor
swing link
a multiple stage refrigerant system has more than one
compressor
when selecting a replacement compressor you need to make sure the replacement will operate with/at the proper
discharge pressure
among reciprocating compressor the crankshaft is usually vertical in a ___ compressor but horizontal in a ___ compressor
full hermetic; open
on the pistons of reciprocating compressors, the ___ rings prevent oil from reaching the compression chamber. The ___ ring prevent refrigerant from escaping around the piston during compression
bottom; top
which of the following is a method of distributing lubricating oil in a reciprocating compressor
crankshaft splash
a cylinder unloader reduces the capacity of a reciprocating compressor by allowing refrigerant to flow through the ___ port during the ___ stroke
suction; compression
one way of reducing vibration problems in a reciprocating compressors involves the use of
spring mounts
one advantage of rotary compressors over reciprocating compressors is that the
vibration is less
slugging is the entry of ___ refrigerant into a compressor. Cavitation is the formation and collapse of ____ in a liquid flowing under pressure
liquid; vapor pockets
one purpose of the accumulator on a rotary compressor is to
keep dirt and debris out of the compressor
helical compressors differ from rotary compressors in that they have
no vanes
in a scroll compressor one scroll is stationary and the other ___ refrigerant enters the scrolls at the __ and leaves at the center
orbits; outer edge
the amount of compression in a centrifugal compressor depends on the ___ the impeller, which depends in turn on the impellers ___ and rate of rotation
tip speed of; diameter
in reverse hydrostatic sealing the flow of ___ across the seal opposes the flow of ____ across the bearing
refrigerant vapor; oil
in multistage centrifugal compressors thrust loads are reduced by
opposing impellers
the purpose of a purge system on a condenser is to eliminate ___ from the refrigeration system
air
reducing a compressors capacity by closing pre rotation vanes raises the pressure in the systems ___
evaporator
which of the following is an important factor to consider when selecting a motor to tun a refrigeration compressor
horsepower rating
which of the following motors can be used in hermetic compressors
capacitor start, induction run
you can reverse the direction of a single phase induction motor by
reversing the connection of either the starting or running winding
to change a dual voltage motor to run on 240v instead of 120v you need tp
connect the two running windings in series
a single phase motor used in a hermetic compressor has a relay to disconnect the starting winding from the circuit when the motor approaches its running speed. One kind of relay operates when the current in the ___ winding falls to a preset value. Another kind operates when the voltage across the ___ winding rises to a preset value
running; starting
the two basic categories of motor starting devices are
contactors and starters
a reduced voltage starter limits the current to the motor at startup in order top prevent
voltage drops to other equipment
overload protection for compressor motors may be provided by a
external bimetallic disk
crankcase heaters are especially useful on compressors that are subjected to
cold climates
installing a suction line accumulator can protect a compressor from damage caused by
slugging
the first rule of preventative maintenance for all compressors and related components is to
follow the manufacturers recommended maintenance schedules and procedures
typical preventative maintenance procedures from compressors are related equipment include
listening for unusual sounds
a compressor may overheat because of a
low oil level
when pumping down a compressor for service run the compressor with the valve on the suction line closed then close the valve on the discharge line and stop the compressor. Repeat this process until the pressure holds at ___ psig
+2 to +5
After disassembling a reciprocating compressor and cleaning the parts you should inspect the parts for
excessive wear on bearing surfaces
