Page 24 - Uninterruptible Power Supplies

Standby Power Generating Sets
22 Chapter One

pump is installed between the daily service tank and the bulk tank,
the pump being controlled from start/stop level controls in the daily ser-
vice tank. To avoid spillage of fuel in the event of failure of the level con-
trols, an overflow pipe returns surplus fuel back to the bulk tank. There
should be a manual shutoff valve in the supply pipe to allow for occa-
sional maintenance of the electric pump and any other items installed in
the supply pipeline. The daily service tank should have a filler cap and
vent, the filler cap is available for emergency use if the pump fails, or if
the bulk tank is empty or not available for use. It is most important that
the overflow pipe be large enough to allow the free flow of the maximum
quantity of fuel that can be delivered by the pump. This should be demon-
strated during the commissioning procedure.
If the bulk tank is mounted above the daily service tank, Fig. 1.10
indicates the basic interconnecting requirements. The fuel level within
the service tank is maintained by a solenoid valve in the supply pipe run
and open/close level controls within the service tank. The service tank
and the associated pipework should be pressure tested for the maxi-
mum static pressure that can arise if the level controls or the solenoid
valve fail. A vent pipe from the daily service tank is taken back to the
bulk tank, or is vented to atmosphere above the level of the bulk tank;
it follows that there cannot be a spillage of fuel from the service tank
unless there is a failure of the pipework or of the tank. There should be
a manual shutoff valve in the supply pipe to allow for occasional main-
tenance of the daily service tank and any items installed in the supply
pipeline.
Although reliance on gravity may appear to simplify the installation,
this is not the preferred arrangement. The failure of the solenoid valve
results in the service tank being subject to the full static pressure from
the bulk tank. Even a slow leakage through the valve can, between test
runs, result in the service tank being full and the vent pipe being full
of fuel to the level of the bulk tank. For these reasons a filler point can-
not be allowed on the service tank, there is no way of ensuring that it
is properly replaced. It follows that if there is only one bulk tank and it
is empty or out of use, manually filling the service tank presents a prob-
lem. Temporary arrangements will normally have to be made within
the engine room, alternatively permanent pipework could link the ser-
vice tank to a remote fill point at the same level as the bulk tank.
Remote filling requires a communication link between the fill point and
the engine room.
Bulk storage tanks are usually cylindrical, mounted horizontally
with a slight incline, fuel being taken off from the higher end while a
water drain point or sludge cock at the lower end allows water and
sludge to be drawn off. There should be local or remote indication of the
contents, a filling point and an access manhole, raised above the tank

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