Compressed Air Systems

References Required Introduction to Naval Engineering (Ch 18). Optional: Principles of Naval Engineering (Ch 3. Pg ).

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 (PV  RT) Used to compress air from inlet pressure (atm) to a higher pressure (PV  RT) Classified according to: – Type of displacement – Staging – Type of Drive (prime mover) – Operating Pressure – Capacity

Air Compressors Type of displacement 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 Type of drive system – Classified according to prime mover (almost all electric motors) Staging Staging – Number of compression steps used in compression process Number of StagesPressure (psig) One Two Three Four

Air Compressors Operating (discharge) pressure Operating (discharge) pressure – Low (150 psi max) – Medium ( psi) – High ( psi) Capacity Capacity – Volume of air compressed – CFM (cubic feet per minute)

Positive Displacement Reciprocating Piston 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.