Compressors

Question 1

What are the 3 Drive types

Answer 1

1. Open Drive Compressor
2. Hermetic Compressor
3. Semi Hermetic Compressor

Question 2

Types of compressors

Answer 2

1. Reciprocating
2. Scroll
3. Rotary (rotating vayne and stationary blade)
4. Screw
5. Centrifugal

Question 3

How much oil can compressor lose upon start up ?

Answer 3

5-7%

Question 4

What is the maximum discharge temp for compressors ?

Answer 4

225 farenheight

Question 5

5 tons and below are “usually” what types of compressors ?

Answer 5

Reciprocating, rotary and scroll

Question 6

10-100 tons are “usually” what ?

Answer 6

Reciprocating and Screw

Question 7

Over 100 tons are usually what type of compressor ?

Answer 7

Centrifugal

Question 8

Types of open drive compressors

Answer 8

1. Belt drive
2. Direct Drive

Question 9

What do open drive compressors have that other typically don’t require ?

Answer 9

Shaft seal because the crankshaft extends through the compressor body so it can connect to the drive motor

Question 10

In what types of equipment are rotary compressors commonly found ?

Answer 10

Small refrigeration appliances

Question 11

What is the purpose of a shaft seal on open drive compressors?

Answer 11

Shaft seal is designed to prevent leaks and can withstand varying pressures. Seal must be lubricated and is a common failure point.

Question 12

How are hermetic compressors cooled ?

Answer 12

Typically suction cooled
Can be cooled via air and water

Question 13

Are semi hermetic compressors serviceable?

Answer 13

Yes, they are enclosed in a bolt assembly

Question 14

Why do hermetic compressors have a greater pumping capacity ?
How are they lubricated?

Answer 14

Because they run at a higher RPM.
Lubricated by oil in the refrigerant.

Question 15

What are the types of crankshafts for reciprocating compressors?

Answer 15

1. Eccentric type
2. Crank throw type
3. Scotch yoke

Question 16

Valve types ?

Answer 16

1. Reed valve
2. Poppet valve
3. Discuss valve
4. Ring valve

Question 17

What applications are reciprocating compressors used for ?

Answer 17

1. Domestic
2. Commercial
3. Industrial
   (Highly versatile)

Question 18

In what compressor(s) is a check valve installed on the discharge side of the compressor to prevent equalization in the off cycle ?

Answer 18

Rotary compressor, scroll compressor

Question 19

Common applications for scroll compressors ?

Answer 19

Residential, commercial air conditioning/heat pump applications

Question 20

Benefits of a scroll compressor ?

Answer 20

Fewer moving parts, less internal friction, smooth compression cycle

Question 21

Which compressor has no internal suction valve ?

Answer 21

Scroll

Question 22

How does a screw compressor work?

Answer 22

Helical rotors compress refrigerant Vapor.

Male rotor has 4 lobes.
Female rotor drives male rotor

Question 23

Which compressor uses oil injection and why ?

Answer 23

Screw compressor

To provide a seal to prevent leaks and help cool the compressor.

Question 24

Why do screw compressor typically have lower discharge temperatures ?

Answer 24

Because of the large amounts of oil used for lubrication.

Question 25

Lower compression rate = what ?

Answer 25

The more efficient and cooler the compressor will operation

Question 26

How does a suction valve open ? How does a discharge valve open ?

Answer 26

1.When the volumetric pressure decreases inside the compressor chamber 2. When the volumetric pressure increases inside the compressor chamber

Question 27

What do connecting rods do ?

Answer 27

1. Connect the piston to the crankshaft 2. Bearing provide low friction surface

Question 28

Connecting rods for crank throw crankshaft ?

Answer 28

Split end clamps around journal or crank throw

Question 29

Connecting rods for crank throw crankshaft ?

Answer 29

Split end clamps around journal or crank throw

Question 30

Connecting rods for eccentric crankshaft ?

Answer 30

End is solid ring

Question 31

Non positive displacement compressor ?

Answer 31

Centrifugal chiller

Question 32

How many impellers do centrifugal have and what is the rpm range ?

Answer 32

1-4 impellers that rotate between 3000-20,000 RPM.

Question 33

Purpose of crankcase heaters?

Answer 33

Warms compressors crankcase, evaporates liquid refrigerant trapped in oil

Question 34

How do centrifugal chillers work?

Answer 34

1. Vapor is fed into the casing (stator) in the Center. 2. Impeller spins rapidly in the casing. 3. Centrifugal force throws Vapor outward causing compression.

Question 35

What is the stator in a chiller ?

Answer 35

Casing in which impeller rotates. Volute design (spiral)

Question 36

What is the stator in a chiller ?

Answer 36

Casing in which impeller rotates. Volute design (spiral)

Question 37

Impeller in a centrifugal chiller ?

Answer 37

Keyed to compressor shaft. No Vapor-trapping pockets. Designed to move more Vapor’s without going above gas velocity limits

Question 38

Which reciprocating compressor crankshaft has no connecting rod ?

Answer 38

Scotch yoke

Question 39

Types of piston rings

Answer 39

1. Upper rings (compression rings) Prevent pressurized refrigerant from blowing past the piston into the crankcase 2. Lower ring (oil ring) Helps lubricated the cylinder wall while simultaneously preventing excess lubricant from entering the cylinder.

Question 40

Poppet valves are only suitable for what speed compressors ?

Answer 40

Low speed since they move slowly

Question 41

What serves as a pressure plate, sealing the top of the cylinder so that the refrigerant can be compressed ?

Answer 41

Cylinder Head

Question 42

What reduces noise that may be caused by gas pulsation ?

Answer 42

Muffler Brazed cylinders with baffle plates mounted inside and allows the gas to expand “smooth the flow”

Question 43

What are “O” rings commonly used for ?

Answer 43

Used as sealing devices, especially where there may be some motion between the assembled parts.

Question 44

What is an “unloader”

Answer 44

Mechanism that temporarily reduces the pressure in the compressor during start up.

Question 45

What is the purpose of oil failure control ?

Answer 45

Shuts off the compressor if oil is not being circulated properly. (Understand how it works/wired)