7.10 Compressed Air - 7.10 Compressed Air

Question 1

Classes of Compressed Air Systems

Answer 1

Low-Pressure (LP) Air: 150 psig or less
-Tan color
Medium Pressure (MP) Air: 151-1000 psig
-Tan color
High Pressure (HP) Air: >1000 psig
-Dark Grey

Question 2

Methods to compress air

Answer 2

Positive displacement
Dynamic method

Question 3

Positive Displacement

Answer 3

Employs pistons, vanes, screws, or lobes that move or rotate within a cylinder or housing and take successive scoops, or volumes of air, and force the air into a smaller volume.

Reciprocating
Rotary

Question 4

Dynamic Method

Answer 4

Do not have valves or ports that open and close. They take in a continuous flow of air and accelerate the air by means of impellers rotating at high speed.

Centrifugal: LPACs
Axial: Compression stage of gas turbines

Question 5

High-Pressure (HP) Air System

Answer 5

A system which is designed for a nominal operating pressure above 1,000 psig

Question 6

High Pressure Air Compressor (HPAC)

Answer 6

Multi-stage reciprocating compressor
Rated to maintain system pressure of 3,000 psig (4,200 psig on carriers)

Question 7

High Pressure Air Uses

Answer 7

5” gas ejection
Torpedo tubes
VLS Deluge
Starting air for diesel and gas turbine engines
Ship service air backup
Emergency lube oil pump coast down
Emergency pneumatic system for air motor-operated valves
Air for helicopter services
Oxygen-Nitrogen (O2N2) Producer air system supply
SCBA

Question 8

Medium Pressure Air Plant

Answer 8

Primarily function: Diesel start air
Secondary function: Augmenting LP air systems
-Not advisable except in case of emergency
Multi-stage reciprocating, oil lubricated compressor
Operates similar to HPAC
Utilized primarily on LPD-17 and MCM class ships

Question 9

Low Pressure Air Plant (LPAP)

Answer 9

There are two concepts in the design of an LP air system:
-Control air / Ship’s service air (CVN/LHD)
-Vital / Non-vital air main (CG/DDG/LPD/LSD)
Rotary, single-screw, water-flooded compressor
-Rated for 125 psig

Question 10

Control Air System

Answer 10

Supplies LP air for the more critical functions having the highest priority such.

1. Air-operated valves
2. Pneumatic controls
3. Automatic combustion and feed water controls
4. Clutch and speed control
5. Maneuvering valves
6. Engine room cutoff valves
7. Governor actuators
8. Shaft brakes and pitch systems

Question 11

Ship Service Air System

Answer 11

Supplies LP air by way of ship service air main to all miscellaneous equipment and services which can tolerate and operate satisfactorily with interruption of the air service.

1.Pneumatic tube dispatch system
2. Aviation lube oil blow-back
3.Windshield wiper pressure tank
4. Filter lubricators of pneumatic hoists
5. Hydraulic test stand and hose burst cabinet
6. Blowing out dry piping of sprinkling systems
7. Hose connections for operation of pneumatic tools
8. Hose connections for cleaning electrical equipment
9. Hose connections for spray guns in filter cleaning stations
10. Deck-edge elevator locks
11. Tank liquid level gages
12. Torpedo room services
13. Laundry equipment
14. Underwater log trunk
15. Sonar dome services
16. Supply for sea chest blow-out

Question 12

Vital/Non-vital air concept

Answer 12

Increasing demands for LP air has resulted in the inability of installed LP air systems to maintain the required minimum air pressures and flow rates to all vital services
Contributing factor for this problem is the inability of a ships service air/control air concept to distribute air on a priority basis

Question 13

Vital/Non-vital air Priority Valve

Answer 13

Ensures LP air capacity is made available for vital services before allowing any air to the non-vital air main
Installed in the cross connection between vital and non-vital air mains
If air use exceeds air production, pressure drops

Starts closing at 100 psig
Completely closed at 85 psig

Question 14

Vital Air Uses

Answer 14

Air-condition plant controls
Air-operated (pneumatic) valves and controls
Combustion and feedwater control air
Air-operated hoists and bridge cranes
Sonar dome pressurization
TLI service
Engineroom and pilot house control stations
Clutch and speed control
Electronics dry air
Aviation support:
-Aircraft elevator locks
-CAT steam accumulator fill and blowdown
-CAT control air charging panel
-Arresting gear anchor damper system
-CAT steam riser quick close valve
-Barricade tensioning air motor hose valve stations

Question 15

Non-Vital Air Uses

Answer 15

Pneumatic tools
Cleaning stations
VLS deluge
Expansion tank pressurization
Sea chest blowout
Pilot house window washing tank
Blow back of fuel hose
Blowing out dry piping of sprinkler systems
Laundry services
Filter cleaning station
Standby supply for CHT aeration
HELO services and maintenance
Air operated hoists
Ships whistle
Air test fitting
Lube oil coast down pump

Question 16

HP Air Backup

Answer 16

An emergency backup source of LP air is cross-connected to the control or vital air main from the HP air system by way of a 3,000 / 80 psig pressure reducing manifold
This feature makes HP air available when control air or vital air pressure drops to 80 ±5 psi or the priority valve has isolated the non-vital air main and drops below 85 psi

Question 17

Weapons System High Pressure Air Compressor (WSHPAC)

Answer 17

Used instead of HP Air System/HPACs on Flight IIA DDGs
Uses:
-Torpedo Tube Charging
-5-inch Gun Gas Ejection
-2 SCBA Recharging Stations

Question 18

Redundant Independent Mechanical Start System (RIMSS)

Answer 18

Takes the place of HP air systems and auxiliary power unit based starting systems on DDGs
Completely independent system used as a primary means of starting the first GTG

Question 19

Air System Safety

Answer 19

Never use combustible cleaning solvents for cleaning compressor parts

Isolate, relieve all pressure, and tag out before working on any portion of a compressed air system

See NSTM 551, manufacturer’s technical manuals, Planned Maintenance System (PMS) and Engineering Operational Sequencing System (EOSS)

Never point HP/LP hoses at personnel or yourself!