Compressor Test
 

We have organized 100 questions to test yourself and others on basic compressor knowledge. The material covers reciprocating compressors, rotary screw compressors, air piping, safety valves, receiver tanks, heat exchangers, drains and many other topics.
 

Sample Questions

The questions are true and false as well as multiple choice. Here are a few of the questions from the test:

Aftercoolers will remove approximately 70% of the water vapor in compressed air. They do this by:

a) Very effective filtration
b) A mechanical separator with a water vapor filter
c) Cooling the air
 

Air receivers store high pressure air. They are built to “ASME Code” and approved. All receivers are ASME Code.

True – or – False

A safety valve should generally have a psig rating of about 10% above the rated or applied pressure and be sized to flow the rated CFM capacity. These ratings are always marked on an approved safety valve.

True – or – False

The centrifugal unloader on a tank mounted compressor will allow the motor and compressor to reach a predetermined minimum RPM before the compressor can “load up”. It also will release the air in the cylinder/head when the compressor stops.

True – or – False

A surface pyrometer is very important in diagnosing compressor systems because it reads:

a) Friction of air in pipe
b) Velocity of the air
c) Surface temperature
 

The term “ring gap” is the:

a) Distance between the end of the piston ring on the workbench.
b) Distance between the inside diameter of the piston ring, and the bottom of the ring groove in the piston.
c) Distance between the end of the piston ring, when it is in the cylinder.
 

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All safety valves should be marked with both capacity (CFM) and pressure rating (PSIG). If they are not marked, it is ok to use them if the packaging has the rating information.

True – or – False

A safety valve must be installed on (check all that apply):

a) Intercooler
b) The straight run of pipe from the compressor discharge to the receiver tank
c) The air receiver tank
d) The inlet pipe
e) In the discharge pipe between the compressor and any shut off valve

Not enough head clearance in a reciprocating compressor can cause:

a) High temperature
b) Scaring of the cylinder
c) Knocking

Too much head clearance in a reciprocating compressor can cause:

a) High temperature
b) Scaring of the cylinder
c) Knocking

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Some compressors are driven by “V Belts”. A well seated belt will be fitted down in the groove with the bottom edge firmly engaging the bottom of the drive sheave or pulley.

True – or – False

Some compressor control systems require compressed air for pressure sensing and regulation. If this air is drawn from a receiver tank, it is best to take it from:

a) The top of the tank
b) The bottom of the tank
c) The side of the tank

Condensation forms during the compression process. This should be drained from the system at (check all that apply):

a) The aftercooler separator
b) The receiver tank
c) The air dryer
 

The best type of drain for a compressed air system is:

a) Timer drains
b) Manual valves
c) Level activated, automatic drains

Select the appropriate type of filter to handle rust, scale or dirt contamination from the air piping.

a) Separator filter
b) Particulate filter
c) Coalescing filter
d) Adsorption filter

Select the appropriate type of filter to handle oil or water aerosol contamination.

a) Separator filter
b) Particulate filter
c) Coalescing filter
d) Adsorption filter

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If the air dryer is a refrigerated type, a particulate filter should be installed before the dryer, and a coalescing filter installed after the dryer.

True – or – False

If the air dryer is a desiccant type, a coalescing filter should be installed before the dryer, and a particulate filter installed after the dryer.

True – or – False

In an oil injected rotary screw compressor, the oil is used for (check all that apply):

a) Sealing the rotors
b) Lubricating the moving parts
c) Improving the filtration of the air flow
d) Cooling the compression chamber

An inlet filter that has been in service for an extended period of time, and shows very little pressure drop will likely be:

a) Extremely restricted
b) Allowing air to bypass the filter, and enter through the sealing areas
c) Functioning properly

In an oil injected rotary screw compressor, a 20° F increase in operating temperature can cut the service life of the oil by 50%.

True – or – False

In an oil injected rotary screw compressor, a 1% water contamination of the oil supply can reduce bearing life by as much as 40%.

True – or – False

There is no need to install an air receiver tank between a rotary screw and a reciprocating compressor.

True – or – False

It is very important to remove all the old oil when changing the oil in an oil injected rotary screw compressor. This means taking steps to completely drain (check all that apply):

a) The oil cooler
b) The oil sump
c) The lowest point in the oil piping

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The best way to make sure an oil change removes all the sediment, is to:

a) Change the oil first thing in the morning, after the compressor has been sitting all night without running
b) Change the oil after the compressor has run for awhile, and the oil has heated up

The oil level gauge should be read while the oil injected rotary screw compressor is:

a) Stopped
b) Running

Which of the following is not likely to cause an increase in the operating temperature of an oil injected rotary screw compressor.

a) Broken thermostatic valve
b) Faulty air oil separator
c) A plugged oil cooler
d) Low oil level
e) Varnish build-up in the airend

A restriction in the inlet air filter or a plugged air oil separator element can lower the CFM output of an oil injected rotary screw compressor, below its rated capacity.

True – or – False

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