NYC DOB A 35 AIR COMPRESSOR
COF EXAM 150 ITEMS WITH
CORRECT VERIFIED ANSWERS
AND DETAILED RATIONALES
INSTANT DOWNLOAD GRADE A+
Practice Question 1: What is the primary function of an air
compressor?
A) To cool down air B) To increase the pressure of air by reducing
its volume C) To filter impurities from water D) To generate electricity
Correct answer: B - An air compressor mechanically increases
the pressure of air by reducing its volume, storing potential energy.
Practice Question 2: Which type of compressor uses a rotating
impeller to accelerate air and then convert velocity into pressure?
A) Reciprocating compressor B) Centrifugal compressor C) Screw
compressor D) Diaphragm compressor
Correct answer: B - Centrifugal compressors use high-speed
impellers to accelerate air, converting kinetic energy into pressure in a
diffuser.
Practice Question 3: What is the purpose of an aftercooler in a
compressed air system?
A) To heat the air before storage B) To remove heat and condense
moisture from the compressed air C) To increase the pressure
further D) To lubricate the pistons
Correct answer: B - Aftercoolers reduce the temperature of
discharged air, causing moisture to condense so it can be removed via
drains.
Practice Question 4: According to OSHA and ASME standards, what
safety device must be installed on every air receiver tank?
,A) Pressure gauge only B) Safety relief valve C) Thermostat D) Flow
meter
Correct answer: B - A safety relief valve is mandatory to prevent
over-pressurization and potential tank rupture.
Practice Question 5: What is "dew point" in the context of
compressed air?
A) The temperature at which air freezes B) The temperature at
which water vapor begins to condense into liquid C) The
maximum operating temperature of the compressor D) The temperature
of the ambient air
Correct answer: B - Dew point is the temperature at which air
becomes saturated with water vapor, leading to condensation.
Practice Question 6: Which component is responsible for separating
oil from compressed air in a lubricated screw compressor?
A) Intake filter B) Oil separator/coalescing filter C) Aftercooler D)
Unloader valve
Correct answer: B - The oil separator removes entrained oil from
the compressed air stream before it enters the distribution system.
Practice Question 7: What is the likely result of operating a
compressor with a clogged intake filter?
A) Increased efficiency B) Reduced capacity and increased energy
consumption C) Higher discharge pressure D) Lower operating
temperature
Correct answer: B - A clogged filter restricts airflow, forcing the
compressor to work harder, reducing efficiency and increasing heat.
Practice Question 8: In a reciprocating compressor, what is the
function of the unloader valve?
A) To release pressure from the tank B) To allow the compressor to
start under no-load conditions C) To regulate the speed of the
motor D) To inject oil into the cylinder
Correct answer: B - The unloader valve vents pressure from the
cylinder head during startup to reduce starting torque on the motor.
,Practice Question 9: What is the standard color code for compressed
air lines in many industrial facilities?
A) Red B) Green C) Yellow or Blue (depending on facility
standard, often Yellow for caution/air) D) Black
Correct answer: C - While standards vary, Yellow is commonly
used for compressed air to indicate caution, though some facilities use
Blue. Always check local facility standards.
Practice Question 10: Why is it dangerous to use compressed air to
clean clothing?
A) It wastes air B) It can force air into the bloodstream through
skin breaks or cause eye injury C) It damages the fabric D) It
creates static electricity
Correct answer: B - Compressed air can penetrate skin or eyes,
causing serious injury or embolism, and is prohibited by OSHA for
cleaning clothes.
Practice Question 11: What does "CFM" stand for in compressor
specifications?
A) Cubic Feet per Minute B) Cubic Feet per Minute C) Compressed
Force Measurement D) Cylinder Flow Metric
Correct answer: A - CFM measures the volume of air flow
delivered by the compressor.
Practice Question 12: What is the purpose of a condensate drain trap?
A) To add water to the system B) To automatically remove
accumulated water and oil from the receiver or filters C) To
measure pressure D) To cool the motor
Correct answer: B - Drain traps automatically eject condensed
liquids (water/oil) to prevent them from entering the air distribution
system.
Practice Question 13: Which type of compressor is best suited for
continuous, high-volume applications?
A) Reciprocating piston B) Rotary screw C) Diaphragm D) Small
portable electric
, Correct answer: B - Rotary screw compressors are designed for
continuous duty and high-volume output with less vibration than
reciprocating types.
Practice Question 14: What is the risk of excessive moisture in a
compressed air system?
A) Improved lubrication B) Corrosion of pipes and damage to
pneumatic tools C) Increased air density D) Better cooling
Correct answer: B - Moisture causes rust, corrodes components,
washes away lubrication, and can freeze in cold environments.
Practice Question 15: What is the function of the pressure switch in a
small compressor?
A) To measure temperature B) To turn the motor on and off based
on set pressure limits C) To filter the air D) To regulate oil flow
Correct answer: B - The pressure switch monitors tank pressure
and starts/stops the motor to maintain pressure within the cut-in/cut-
out range.
Practice Question 16: What is "free air delivery" (FAD)?
A) Air given away for free B) The actual volume of air delivered by
the compressor at inlet conditions C) Air released from the safety
valve D) Air measured at discharge pressure
Correct answer: B - FAD is the volume of air drawn into the
compressor, measured at ambient temperature and pressure.
Practice Question 17: Why must air receivers be inspected regularly?
A) To paint them B) To check for corrosion, cracks, and
structural integrity C) To change the color D) To increase capacity
Correct answer: B - Regular inspections prevent catastrophic
failure due to internal corrosion or metal fatigue.
Practice Question 18: What is the purpose of an intake silencer?
A) To increase pressure B) To reduce noise and filter incoming air
C) To cool the air D) To separate oil
COF EXAM 150 ITEMS WITH
CORRECT VERIFIED ANSWERS
AND DETAILED RATIONALES
INSTANT DOWNLOAD GRADE A+
Practice Question 1: What is the primary function of an air
compressor?
A) To cool down air B) To increase the pressure of air by reducing
its volume C) To filter impurities from water D) To generate electricity
Correct answer: B - An air compressor mechanically increases
the pressure of air by reducing its volume, storing potential energy.
Practice Question 2: Which type of compressor uses a rotating
impeller to accelerate air and then convert velocity into pressure?
A) Reciprocating compressor B) Centrifugal compressor C) Screw
compressor D) Diaphragm compressor
Correct answer: B - Centrifugal compressors use high-speed
impellers to accelerate air, converting kinetic energy into pressure in a
diffuser.
Practice Question 3: What is the purpose of an aftercooler in a
compressed air system?
A) To heat the air before storage B) To remove heat and condense
moisture from the compressed air C) To increase the pressure
further D) To lubricate the pistons
Correct answer: B - Aftercoolers reduce the temperature of
discharged air, causing moisture to condense so it can be removed via
drains.
Practice Question 4: According to OSHA and ASME standards, what
safety device must be installed on every air receiver tank?
,A) Pressure gauge only B) Safety relief valve C) Thermostat D) Flow
meter
Correct answer: B - A safety relief valve is mandatory to prevent
over-pressurization and potential tank rupture.
Practice Question 5: What is "dew point" in the context of
compressed air?
A) The temperature at which air freezes B) The temperature at
which water vapor begins to condense into liquid C) The
maximum operating temperature of the compressor D) The temperature
of the ambient air
Correct answer: B - Dew point is the temperature at which air
becomes saturated with water vapor, leading to condensation.
Practice Question 6: Which component is responsible for separating
oil from compressed air in a lubricated screw compressor?
A) Intake filter B) Oil separator/coalescing filter C) Aftercooler D)
Unloader valve
Correct answer: B - The oil separator removes entrained oil from
the compressed air stream before it enters the distribution system.
Practice Question 7: What is the likely result of operating a
compressor with a clogged intake filter?
A) Increased efficiency B) Reduced capacity and increased energy
consumption C) Higher discharge pressure D) Lower operating
temperature
Correct answer: B - A clogged filter restricts airflow, forcing the
compressor to work harder, reducing efficiency and increasing heat.
Practice Question 8: In a reciprocating compressor, what is the
function of the unloader valve?
A) To release pressure from the tank B) To allow the compressor to
start under no-load conditions C) To regulate the speed of the
motor D) To inject oil into the cylinder
Correct answer: B - The unloader valve vents pressure from the
cylinder head during startup to reduce starting torque on the motor.
,Practice Question 9: What is the standard color code for compressed
air lines in many industrial facilities?
A) Red B) Green C) Yellow or Blue (depending on facility
standard, often Yellow for caution/air) D) Black
Correct answer: C - While standards vary, Yellow is commonly
used for compressed air to indicate caution, though some facilities use
Blue. Always check local facility standards.
Practice Question 10: Why is it dangerous to use compressed air to
clean clothing?
A) It wastes air B) It can force air into the bloodstream through
skin breaks or cause eye injury C) It damages the fabric D) It
creates static electricity
Correct answer: B - Compressed air can penetrate skin or eyes,
causing serious injury or embolism, and is prohibited by OSHA for
cleaning clothes.
Practice Question 11: What does "CFM" stand for in compressor
specifications?
A) Cubic Feet per Minute B) Cubic Feet per Minute C) Compressed
Force Measurement D) Cylinder Flow Metric
Correct answer: A - CFM measures the volume of air flow
delivered by the compressor.
Practice Question 12: What is the purpose of a condensate drain trap?
A) To add water to the system B) To automatically remove
accumulated water and oil from the receiver or filters C) To
measure pressure D) To cool the motor
Correct answer: B - Drain traps automatically eject condensed
liquids (water/oil) to prevent them from entering the air distribution
system.
Practice Question 13: Which type of compressor is best suited for
continuous, high-volume applications?
A) Reciprocating piston B) Rotary screw C) Diaphragm D) Small
portable electric
, Correct answer: B - Rotary screw compressors are designed for
continuous duty and high-volume output with less vibration than
reciprocating types.
Practice Question 14: What is the risk of excessive moisture in a
compressed air system?
A) Improved lubrication B) Corrosion of pipes and damage to
pneumatic tools C) Increased air density D) Better cooling
Correct answer: B - Moisture causes rust, corrodes components,
washes away lubrication, and can freeze in cold environments.
Practice Question 15: What is the function of the pressure switch in a
small compressor?
A) To measure temperature B) To turn the motor on and off based
on set pressure limits C) To filter the air D) To regulate oil flow
Correct answer: B - The pressure switch monitors tank pressure
and starts/stops the motor to maintain pressure within the cut-in/cut-
out range.
Practice Question 16: What is "free air delivery" (FAD)?
A) Air given away for free B) The actual volume of air delivered by
the compressor at inlet conditions C) Air released from the safety
valve D) Air measured at discharge pressure
Correct answer: B - FAD is the volume of air drawn into the
compressor, measured at ambient temperature and pressure.
Practice Question 17: Why must air receivers be inspected regularly?
A) To paint them B) To check for corrosion, cracks, and
structural integrity C) To change the color D) To increase capacity
Correct answer: B - Regular inspections prevent catastrophic
failure due to internal corrosion or metal fatigue.
Practice Question 18: What is the purpose of an intake silencer?
A) To increase pressure B) To reduce noise and filter incoming air
C) To cool the air D) To separate oil
