Compressed Air Systems

References

Required•Introduction to Naval Engineering (Ch 18). Optional:•Principles of Naval Engineering (Ch 3. Pg. 71-74).

Introduction

• Air systems are vital to ship operations– Starting diesel and gas turbine engines– Torpedo ejection– Deballasting air (EMBT Blow)– Prairie masker

• Compressed air represents stored energy - capable of doing work at a later point

• Used extensively both in high pressure and low pressure applications

Air Compressors

• Used to compress air from inlet pressure (atm) to a higher pressure (PV a RT)

• Classified according to:– Type of displacement– Staging– Type of Drive (prime mover)– Operating Pressure– Capacity

Air Compressors• Type of displacement– Positive: used for high pressures

– aka HPACs and LPACs

– Non-positive: used for lower pressures– aka fans and blowers

• Type of drive system– Classified according to prime mover (almost all

electric motors)• Staging– Number of compression steps used in

compression processNumber of Stages Pressure (psig)

One 100-150

Two 150-500

Three 500-2500

Four 2500-5000

Air Compressors• Operating (discharge) pressure– Low (150 psi max)– Medium (151-1000 psi)– High (1001-5000 psi)

• Capacity– Volume of air compressed– CFM (cubic feet per minute)

Positive Displacement

• Reciprocating Piston– Piston assembly

with valves to control flow

– Can either be single stage or multi-stage

– aka HPAC

Positive Displacement

• Rotary Compressor– Rotary sliding vane

(rare)– Rotary impeller (low

press/ high capacity applications)

– Liquid piston (old ships)

Positive Displacement

• Rotary Compressor– Rotary sliding vane

(rare)– Rotary impeller

(low press/ high CFM applications)– aka LPAC

– Liquid piston (old ships)

Positive Displacement

• Rotary Compressor– Rotary sliding vane

(rare)– Rotary impeller

(low press/ high CFM applications)

– Liquid piston (old ships)

Non-Positive Displacement

• Centrifugal compressor– Radial flow

• Axial Compressor– Axial Flow

Support Systems• Lubrication

– Force-fed compressor-driven system– Prevent metal-on-metal contact to minimize friction/heat– Transfers heat from compression to cooling system

• Cooling– Most cooled by fresh water systems– Remove heat from compression process– Intercoolers used between stages– Aftercooler used after final discharge

• Receivers– Storage tanks for reserve air capacity– Used on ALL compressors to lower pulsations

• Safety features– Auto shutdown

Specific Uses of Air

• High Pressure– Torpedo Ejection– Emergency Blow– Hydraulics– Remotely-operated valves

• Low Pressure– Prairie Masker system – Potable water– Pneumatic tools & valves

Prairie-Masker

Take Aways

• Describe methods for classifying compressed air systems

• List the types of air compressors used• Describe the various support systems• Give 4 shipboard uses of High Pressure Air.