High and Low Pressure Air

Question 1

What are the advantages of compressed air?

Answer 1

Easily distributed around ship
Easily stores
Flexibility and reliability of use
Low risk of fire

Question 2

What are the two categories of high pressure air?

Answer 2

HP air operating at 276 bar

Reduced HP air operating below 276 bar as required by equipment (via reducing valve)

Question 3

What 2 areas can HP air be divided into?

Answer 3

IMS - inside machinery space

OMS - outside machinery space

Question 4

What are the uses of HP air?

Answer 4

Diesel engine starting
Gas turbine starting
Ship siren operation
Breathing apparatus charging
Weapon systems operation
Hydraulic system accumulator charging
Air driven machinery operation
Cross connection to low pressure air system

Question 5

What are the 4 stages of the high pressure air compressor and what are their values?

Answer 5

4 pistons, starting larger, getting smaller. Increasing 4 fold each time. 
Stage 1 - 4 bar
Stage 2 - 17.5 bar
Stage 3 - 68 bar
Stage 4 - 276 bar

Question 6

How is air cooled in a HPAC?

Answer 6

Cooled by intercoolers (sea water cooled heat exchangers) after each stage of compression.

Question 7

What are the 4 stages of pressure relief valves at each stage of compression and which type are used?

Answer 7

10% over stage pressure valve. 
Stage 1 - 4.4 bar
Stage 2 - 19.25 bar
Stage 3 - 74.9 bar
Stage 4 - 303.6 bar

Question 8

How is water removed from the compressor?

Answer 8

Air is passed through drains and separator columns. The air separators automatically drain every 30 minutes of run time.

Question 9

What will the hamworthy compressor warn and stop for?

Answer 9

High water temperature

Low oil pressure

Question 10

At what value will the high water temperature switch operate?

Answer 10

54 degrees c

Question 11

At what value will the low oil pressure switch operate at?

Answer 11

0.69 bar

Question 12

How is the compressor driven?

Answer 12

Via electric motor

Question 13

At what value does the water jacket safety valve operate and what does it do?

Answer 13

3.5 bar, it protects the FW cooling system and SW main from over pressurisation

Question 14

What are the uses of LP air?

Answer 14

Pneumatic tools
Radar wave guides
Emergency stern seal inflation
Pneumatic surveillance panels

Question 15

What are the hazards of HP/LP air?

Answer 15

High pressure air directed towards body can be lethal.
Oil and grease can explode when bought into contact with HP air.
Hoses are flexible and flailing can occur.

Question 16

What are the precautions to be followed when working with HP/LP air?

Answer 16

Never point HP air at anyone.
Ear defenders must be worn.
Silicone grease is used to prevent explosion.
Hoses will be ‘lifed’ with dates stamped on and must be in date.
Hoses must be connected at each end before pressurising.
Unconnected hoses must be ‘whipped’ ie secured at each end to prevent flailing.

Question 17

What safe working practices must be adhered to while filling air bottles?

Answer 17

Bottle must be located in purpose built rack.
Operators must be wearing PPE.
Hoses must be in good condition and connected with the correct spanner.
A good condition O seal must be used.
Bottle should be filled slowly to avoid overheating.

Question 18

What PPE is required when charging bottles from HP air?

Answer 18

Goggles

Ear defenders

Question 19

What value is LP air?

Answer 19

Any value up to 8 bar.

Question 20

What must be done before working on high pressure air?

Answer 20

Two isolating valves each side of work area must be isolated.
System downstream of isolating valves must be drained.
System must be continuously monitored for build up of pressure.
Drain compressor of all water.