REF UNIT 23 Flashcards
(23.2) where are screw compressors used?
in larger commercial and industrial systems
(23.2) how are reciprocating compressors categorized?
open, semi-hermetic, or hermetic
(23.2) what type of drive do hermetic compressors use?
direct drive
(23.2) is the hermetic compressor considered a high side or low side device?
low side
(23.2) how are serviceable compressors usually cooled?
by air
(23.2) what type of motor design does a screw compressor use?
an open motor design
(23.2) how do screw compressors seal refrigerant from atmosphere?
with a shaft seal.
(23.2) how are screw compressor’s compression ratios different from reciprocating?
they aren’t.
(23.2) what is the off centre part of the crankshaft called?
the throw
(23.2) what is an eccentric crankshaft?
have large circles around the shaft I guess
(23.2) what connects the pistons to the crankshaft?
connecting rods
(23.2) what connects the piston to the connecting rod?
wrist pins
(23.2) what is used to keep the wrist pin from sliding against the cylinder wall?
a snap ring
what are the two main types of cylinder valves?
reed valves (flapper valves) and ring valves
(23.2) what are used to muffle compressor pulsation noise?
mufflers
(23.2) what holds the compressor and sometimes the motor?
the compressor housing
(23.2) how do motors protect the compressor housing from being energized?
small compressors use fused glass, large ones use a fiber block sealed with an O-ring.
(23.4) what is the pulley on the motor referred to as?
drive pulley
(23.4) what is the pulley on the compressor referred to as?
the driven pulley
(23.4) what is the formula for calculating pulley relations?
pulley 1 × rpm 1 = pulley 2 × rpm 2
(23.7) why are discus valves more efficient than other valves?
it allows for less clearance volume
(23.7) why do scroll compressors have high SEER ratings?
because they provide a large amount of cooling over the entire season off a low kWh consumption.
(23.7) what are the two scrolls in a scroll compressor referred to as?
involute spirals
(23.7) why can scroll compressors handle some liquid slugging?
the 2 scrolls will separate slightly, which allows some liquid.
(23.7) what is “flank sealing?”
the centrifugal forces and oil forming a seal to prevent gas leakage in a scroll compressor.
(23.7) how does 2-step capacity control on scroll compressors work?
they use a DC solenoid valve
(23.7) what is a TOD?
temperature operated disc. a bimetal disc that opens at 270F.
(23.7) what is an IPR?
internal pressure relief. opens at approximate 400 psi differential in compression ratio.
(23.7) what is a floating seal?
separates high side from low side
