1.5 COMPRESSED AIR
SYSTEMS
? Air at high pressure,i.e,at 25 bar or
more,is required for starting main
and auxiliary engines in motorships,
? Air at low pressure,say at 6 bar or
less is required for much remote or
temperature or pressure controlled
equipment,for which purpose it must
be clean and oil-free.
OIL/WATER
SEPARATOR
1.5 COMPRESSED AIR
SYSTEMS
? A typical simple h.p,air system is shown in
the below Figure; the arrangement of a
larger system can be readily envisaged
from this diagram,
OIL/WATER
SEPARATOR
AIR
COMPRESSORS
FROM
EMERGENCY
COMPRESSOR
ALL AIR COMPRESSORS AND
RECEIVERS TO BE FITTED WITH
SUITABLE SAFETY VALVWS AND
DRAIN VALVES
AUX.
ENGINE
SDNR
VALVE
SDNR
VALVE
AIR
RECEIVER
STOP VALVES ON AIR RECEIVERS
TO BE SLOW OPENING TYPE
MAIN ENGINE
NRV
AUX.
ENGINE
AUX.AIR
RECEIVER
1.5 COMPRESSED AIR
SYSTEMS
? It is a requirement that there shall be at least two
reservoirs whose combined capacity allows the
main engines to be started twelve times if they
are reversible and six times if they are not,while
the compressors are idle,
1.5 COMPRESSED AIR
SYSTEMS
? Safety valves must be fitted; these may be
common to the compressors but if they can be
isolated from the reservoirs,the latter must have
fusible plugs fitted to prevent rupture in the event
of fire,
? Reservoirs are designed,built and tested similarly
to boiler drums,
? Compressors are discussed,two or more,
independently driven,are usually fitted,each
capable of charging one reservoir from zero to
working pressures in a reasonable time.
1.5 COMPRESSED AIR
SYSTEMS
? Explosions can and
do occur in starting
air pipes caused by
the ignition of oil or
vapour gaining
access from
compressors or
defective engine
starting valves,
1.5 COMPRESSED AIR
SYSTEMS
? The need for careful
maintenance,cleaning and
draining is important,
? Bursting discs are fitted
(usually in the form of a
thin copper closed-ended
cylinder) to minimize and
localize the effects.
1.5 COMPRESSED AIR
SYSTEMS
? Starting air for
auxiliary engines
may be taken
directly from the
main reservoirs or
through an
auxiliary reservoir
(which can be kept
at full pressure at
all times).AUX.AIR
RECEIVER
SDNR
VALVE
AIR
RECEIVER
NRV
1.5 COMPRESSED AIR
SYSTEMS
? Low pressure air is usually taken through
reducing valves or pressure regulators to a
low pressure reservoir,
? Alternatively,the l.p,reservoir may be
charged by an oil-free compressor,rotary
or reciprocating.