3.1 It is essential that the fuel system is designed
to accommodate the high pressure pulses which will be generated by
the injection pumps. The engine manufacturer and/or the fuel installation
manufacturer and the piping installer etc. must be consulted for an
explicit statement of the fuel system parameters, including the maximum
pressures which will be generated. Many engine manufacturers, aware
of the potential risks due to high pressure pulses within the fuel
system, now aim to limit the magnitude of the pulses to 16 bar at
the engine fuel rail outlets.
3.2 The alternative approaches which may be considered
by the designer are:
- design of the fuel system such that it is able to contend with
the magnitude of pressure pulses which are generated. Piping systems
should be designed and installed to an appropriate classification
society or ISO specification;
- installation of pressure damping devices; or
- specification of injection pumps which are designed to eliminate
or reduce high pressure pulses.
3.3 The fuel line between the fuel tank and the
engine is made up of several parts from different suppliers. The fact
that these suppliers are unaware of, and therefore do not take into
account, the pressures that may be placed on their equipment by the
other components of the system, is often the reason for the system's
failure. It is recommended, therefore, that a single person is given
responsibility for the co-ordination of the specification, design
and installation of all components within the fuel system, so as to
ensure that they are all suitable for the anticipated high pressure
pulses. It is important that the co-ordinator ensures that the design
intent is fully implemented at the time of on-board installation.
3.4 There are a number of pressure damping devices
which have been fitted within fuel systems. Mechanical pressure accumulators
and gas filled bellows have both been used, however in some cases,
problems of slow response and failure due to fatigue and vibration
have been experienced.
3.5 Fuel pipes should be of steel and supports
should be adequate to prevent fatigue due to vibration through the
structure from the engines and propellers. The support arrangements
should also protect the system from vibration caused by high pressure
pulses. Copper and aluminium-brass pipes should not be used as their
inherent work hardening characteristics make them prone to failure
when subjected to vibration.
3.6 Experience indicates that compression couplings
require careful attention to tightening procedures and torques to
avoid leaks or damage to the pipe when subjected to overtightening.
They should not be used in the fuel supply line of the injection pumps
and spill system. Flanged connections should be used in place of compression
couplings.
3.7 In many cases several engines are supplied
by a single fuel supply pump and if there is a leakage, the watchkeeper
must stop all engines. However, there are occasions when promptly
stopping the engine on which the leak has developed and isolating
its fuel supply and spill lines would suffice. Therefore in multi-engine
installations supplied from the same fuel source, means of isolating
the fuel supply to and spill from individual engines should be provided.
The means of isolation should be operable from the control position.