Pneumatic Systems

Question 1

What are the two (2) main categories of screw compressors?

Answer 1

1. oil-flooded (wet)
2. oil-free (dry)

They may be either single-stage or multi-stage, depending on requirements

Question 2

Which rotor is the driver on a screw compressor?

Answer 2

The male rotor is usually the rotor that is directly driven.

Question 3

What determines the capacity of a screw compressor?

Answer 3

Rotor length, diameter, lobe/flute design and speed determine compressor capacity.

Question 4

What determines the discharge pressure of a screw compressor?

Answer 4

The discharge pressure is determined by the location of the inlet port along the length of the rotor, the length of path along the lobes and flutes and the location of the discharge port.

Question 5

What function does the oil in an oil-flooded screw compressor serve?

Answer 5

Dissipate some of the heat due to compression, seal the gaps between the rotors and the casing to prevent leakage, lubricate the bearings and gearbox and reduce the noise level.

Question 6

Which is the simplest type of control system for screw compressors?

Answer 6

The simplest control system is online/off-line control.

Question 7

Which control system allows the compressor to produce only the amount of air required by the system?

Answer 7

modulation control

Question 8

What must be included to prevent rotor contact in a dry screw compressor?

Answer 8

Timing gears must be used to prevent rotor contact in dry screw compressors.

Question 9

Where are the thrust bearings located on the screw compressor?

Answer 9

The thrust bearings are located at the discharge end.

Question 10

Air filters should be able to remove particles down to what size before the air the compressor?

Answer 10

5 microns

Question 11

What two (2) functions do oil separators perform?

Answer 11

1. Separate oil from the air
2. Act as an oil reservoir and act as an air receiver.

Question 12

What two (2) functions does the minimum pressure valve perform?

Answer 12

1. Maintains a minimum air pressure in the separator
2. Acts as a check valve, preventing flow reversal

Question 13

What is the function of the thermal mixing valve?

Answer 13

to maintain a minimum oil injection temperature.

Question 14

What should be done first before putting a compressor back into service after an overhaul or motor change?

Answer 14

Check for correct rotation after motor or air unit replacement.

Question 15

What is the advantage of the helical lobe blower over the two lobe blower?

Answer 15

increased pressure and smoother air delivery

Question 16

What types of bearings are found on lobe blowers?

Answer 16

Single row ball bearings, double row ball bearings, deep groove ball bearing, spherical roller, cylindrical roller and angular contact bearings can be found on lobe blowers.

Question 17

What should be determined before resetting the timing on a lobe blower?

Answer 17

Before attempting to retime and set lobe clearance, determine whether the unit is unidirectional or bi-directional rotation and always refer to the manufacturer’s operation/maintenance specifications.

Question 18

What should be done before starting a blower after an overhaul?

Answer 18

Turn it over by hand to ensure that it rotates freely in the direction of rotation.

Question 19

Care should be taken to prevent what from happening while you are attempting to set the lobe clearance in a blower?

Answer 19

Take care to prevent injury to the fingers or hands caused by pinching from the gears.

Question 20

The energy of compressed air in the lines can cause severe whiplash when one end of a hose is let free. This can be overcome with an __________
that stops flow through the line if excessive flow occurs.

Answer 20

Excess flow valve

Question 21

What must you do to vertical cylinders before performing any work on or around them?

Answer 21

They must be let down or mechanically blocked to prevent movement

Question 22

Piping should be sized to minimize __________ by being large enough with as few bends as possible.

Answer 22

pressure drop

Question 23

The purpose of a _________
in a pneumatic system is to lower the dew point
so that it does not cause problems in the system.

Answer 23

dryer

Question 24

Why should you use as few bends as possible in pneumatic systems?

Answer 24

To minimize pressure drop

Question 25

What is the function of a dryer in a pneumatic system?

Answer 25

to lower the dew point
so that it does not cause problems in the system.

Question 26

Where can a cyclone separator be used?

Answer 26

Anywhere in the system that moisture might fall out.

Question 27

What is the function of air receivers?

Answer 27

They are used to store compressed air to take up fluctuations in demand and allow the system pressure to vary within reasonable limits.

Question 28

The purpose of the
_______ is to bleed off
excess system pressure before it becomes too extreme.

Answer 28

safety relief valve

Question 29

Why does it matter if there are leaks?

Answer 29

Leaks waste energy (from compression) which increases expenses while reducing the performance of air tools and equipment.

Question 30

Most compressed air systems run for long distances. This allows the air to cool below its _____________ which causes moisture to fall out of the air stream.

Answer 30

dew point

Question 31

Flow control valves control the volume and therefore the speed of the _____________

Answer 31

actuator

Question 32

Pilot operation refers to valves that are operated with _______________.

Answer 32

air pressure

Question 33

____________ piloted means the air pressure within the valve is used to perform the shifting function.

Answer 33

Internally

Question 34

The 3/2 valve can be used if the air needs to be released when the valve is closed. A
typical application is the operation of a _________ acting cylinder.

Answer 34

single

Question 35

A ____________ acting cylinder is a common application of a 4/2 valve.

Answer 35

double

Question 36

The ___________ is used to automatically select the higher of two pressure sources to supply a pneumatic signal.

Answer 36

shuttle valve

Question 37

One of the first items to check in a malfunctioning system is __________________

Answer 37

whether there is a supply of air at sufficient flow and pressure.