REF UNIT 23

Question 1

(23.2) where are screw compressors used?

Answer 1

in larger commercial and industrial systems

Question 2

(23.2) how are reciprocating compressors categorized?

Answer 2

open, semi-hermetic, or hermetic

Question 3

(23.2) what type of drive do hermetic compressors use?

Answer 3

direct drive

Question 4

(23.2) is the hermetic compressor considered a high side or low side device?

Answer 4

low side

Question 5

(23.2) how are serviceable compressors usually cooled?

Answer 5

by air

Question 6

(23.2) what type of motor design does a screw compressor use?

Answer 6

an open motor design

Question 7

(23.2) how do screw compressors seal refrigerant from atmosphere?

Answer 7

with a shaft seal.

Question 8

(23.2) how are screw compressor’s compression ratios different from reciprocating?

Answer 8

they aren’t.

Question 9

(23.2) what is the off centre part of the crankshaft called?

Answer 9

the throw

Question 10

(23.2) what is an eccentric crankshaft?

Answer 10

have large circles around the shaft I guess

Question 11

(23.2) what connects the pistons to the crankshaft?

Answer 11

connecting rods

Question 12

(23.2) what connects the piston to the connecting rod?

Answer 12

wrist pins

Question 13

(23.2) what is used to keep the wrist pin from sliding against the cylinder wall?

Answer 13

a snap ring

Question 14

what are the two main types of cylinder valves?

Answer 14

reed valves (flapper valves) and ring valves

Question 15

(23.2) what are used to muffle compressor pulsation noise?

Answer 15

mufflers

Question 16

(23.2) what holds the compressor and sometimes the motor?

Answer 16

the compressor housing

Question 17

(23.2) how do motors protect the compressor housing from being energized?

Answer 17

small compressors use fused glass, large ones use a fiber block sealed with an O-ring.

Question 18

(23.4) what is the pulley on the motor referred to as?

Answer 18

drive pulley

Question 19

(23.4) what is the pulley on the compressor referred to as?

Answer 19

the driven pulley

Question 20

(23.4) what is the formula for calculating pulley relations?

Answer 20

pulley 1 × rpm 1 = pulley 2 × rpm 2

Question 21

(23.7) why are discus valves more efficient than other valves?

Answer 21

it allows for less clearance volume

Question 22

(23.7) why do scroll compressors have high SEER ratings?

Answer 22

because they provide a large amount of cooling over the entire season off a low kWh consumption.

Question 23

(23.7) what are the two scrolls in a scroll compressor referred to as?

Answer 23

involute spirals

Question 24

(23.7) why can scroll compressors handle some liquid slugging?

Answer 24

the 2 scrolls will separate slightly, which allows some liquid.

Question 25

(23.7) what is “flank sealing?”

Answer 25

the centrifugal forces and oil forming a seal to prevent gas leakage in a scroll compressor.

Question 26

(23.7) how does 2-step capacity control on scroll compressors work?

Answer 26

they use a DC solenoid valve

Question 27

(23.7) what is a TOD?

Answer 27

temperature operated disc. a bimetal disc that opens at 270F.

Question 28

(23.7) what is an IPR?

Answer 28

internal pressure relief. opens at approximate 400 psi differential in compression ratio.

Question 29

(23.7) what is a floating seal?

Answer 29

separates high side from low side