Section 5 - High Pressure Air Compressors and Air Systems

Question 1

What are the stages in a 2 Stage Air Compressor?

Answer 1

• Low Pressure (LP)
• High Pressure (HP)

Question 2

What are the stages in a 3 Stage Air Compressor?

Answer 2

• Low Pressure (LP)
• Intermediate Pressure (IP)
• High Pressure (HP)

Question 3

Explain the operating principles of an air compressor?

Answer 3

Air is drawn through a filter from the atmosphere while the piston in the LP stage is on the downward stroke.

Due to a vacuum being made the suction valve is open and filling the chamber. As the piston comes up the suction valve is closed and the discharge will open due to the increase in pressure.

The air is the delivered to the 2nd stage and the same process begins. On every stage is a relief valve.

A bi-product of compression is heat so on larger air compressors it can be found to be jacket cooled and the air passed via a water intercooler.

Question 4

List 6 safety devices found on an air compressor?

Answer 4

1 Air safety valve on each stage;
2 Intercooler drain on the air side of each stage;
3 Intercooler bursting disc on the water side of each stage jacket.
4 Some cylinder heads have bursting disks
5 Pressure gauge on each stage
6 Fusible plug

Question 5

Explain Volumetric Efficiency?

Answer 5

The ratio of the theoretical volume that can be used to compress the air inside the cylinder to the actual.

Question 6

What can happen if moisture is felt with in the air system?

Answer 6

• Corrosion
• Freezing due to expansion through orifices and subsequent blockage

Question 7

What are the risks with oil carry over?

Answer 7

If the conditions are right it could lead to an explosion in a high pressure system

Question 8

List 4 common alarms and trips on a compressed air system?

Answer 8

• Air temp overheat alarm
• Compressor low Lub Oil pressure cut out
• Compressor Motor Overheat
• Loss of cooling water flow / pressure.

Question 9

What 8 bits of information are typically marked on a cylinder?

Answer 9

• Manufacture
• Serial Number
• Specification
• Date of Manufacture/ Testing
• Water Capacity/ Volume
• Cylinder Weight
• Working Pressure
• Test Pressure

Question 10

What is the standard for testing cylinders?

Answer 10

BS 5430

Question 11

How often should a cylinder be hydraulically tested?

Answer 11

Three years from new then Two years after