Pneumatics

Question 0

Name three types of compressors.

Answer 0

Reciprocating
Screw
Vane Rotary Lobe
Centrifugal

Question 1

There are two main categories of air compressors; what are they?

Answer 1

Positive displacement

Dynamic

Question 2

What is the main advantage that multi-stage compressors have over single stage compressors?

Answer 2

Ability to achieve higher pressures through less heat build-up at high pressures which results in greater efficiency.

Question 3

Name two key characteristics of all good compressor lubricants.

Answer 3

Resist Oxidation
Protect against corrosion
Good lubricity
Low carbon-forming tendencies

Question 4

In an oil-flooded rotary screw compressor, what functions does the lubricant perform? Name 3.

Answer 4

Seals
Cools
Lubricates

Question 5

How do compressors generate water? How do you get rid of it?

Answer 5

Humidity from the air condenses under pressure. It is removed in the coalescer or knock out drum. Also should be drained from aftercooler
and intercooler.

Question 6

Why is a dryer or a knockout drum needed in a pneumatic system?

Answer 6

It removes contaminants and condensed water

Question 7

What is the difference between a double-acting and a single-acting reciprocating compressor?

Answer 7

Double acting compressors have compression on the return stroke.

Question 8

How is volume and pressure controlled in an axial piston?

Answer 8

By adjusting the angle of the swashplate.

Question 9

What is a swashplate?

Answer 9

A component of a piston pump that rotates and causes pistons to move back and forth inside a piston bore.

Question 10

What happens to the temperature of gas as it is compressed?

Answer 10

It increases

Question 11

What should all compressors have on intake?

Answer 11

A Filter

Question 12

What is an FRL?

Answer 12

Filter Regulator Lubricator for an airline oiler

Question 13

What three advantages do rotary vane and rotary screw compressors have over reciprocating compressors?

Answer 13

Quieter
More compact and cheaper to operate
Uniform (non-cyclic) discharge pressures

Question 14

What removes heat generated during compression?

Answer 14

Intercoolers (and the lubricant)

Question 15

What could be the cause of fire and explosion in a compressed air line?

Answer 15

Carbon can build up on discharge valves allowing them to stick open. This causes hot air to get sucked back into the compression chamber where it is recompressed. The air can generate enough heat to ignite the deposits and cause fire or explosion.

Question 16

Name the sequence of events in the compression cycle of a reciprocation air compressor, starting with the piston moving down the cylinder.

Answer 16

Piston moves down, volume increases, inlet valve open, air is drawn into cylinder through inlet valve. Piston reaches bottom of stroke. Inlet valve closes, discharge valve opens. Piston returns, volume decreases, air is compressed. Air is expelled out of the discharge valve. Discharge valve closes. Piston reaches the top of stroke.

Question 17

_______________ act as reservoirs for compressed air.

Answer 17

Receivers

Question 18

What are some important factors to consider when choosing a lubricant for a reciprocation compressor?

Answer 18

Good oxidation stability
Low deposit formation
Correct viscosity
Compatibility with the gas that is being compressed

Question 19

Why is a dryer or knock out drum needed in a pneumatic system?

Answer 19

The air either must be dried prior to compression or a knock out drum installed downstream of the after cooler to prevent condensation. The elimination of moisture is particularly critical when instrument air for pneumatic controls are involved. Moisture removal is also important for pneumatic tools. Wet air promotes rusting and tends to remove oil from lubricated surfaces in contact with air.

Question 20

What does positive displacement mean?

Answer 20

Increase in pressure by reduced volume

Pump output is constant regardless of pressure