Page 315 - Ship Construction.DJ Eyres 6Ed

Ch26-H8070.fm Page 304 Wednesday, October 18, 2006 7:01 AM
304 Ship Construction
single pump room is fitted aft, adjacent to the machinery spaces. The piping
system is of the ‘direct line’ type, three or four lines being provided, each
with suctions from a group of tanks (see Figure 26.4). Each pump discharge
is led up to the deck mains which run forward to the transverse loading and
discharging connections.
A few large tankers have a discharge system which relies on hydraulically
controlled sluice valves in the tank bulkheads. These permit a flow of the oil
with individual suction lines. ารศึกษาเท่านั้น---
to a common suction in the after tank space. Many large tankers partially
adopt this system, sluice valves being provided in the longitudinal bulk-
heads, and the oil is allowed to find its way from the wing tanks to the cen-
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
tre tanks. Suctions from the main cargo lines are located in the centre
tanks. Such an arrangement is shown in Figure 26.4, which also indicates
the separate stripping system, and clean ballast lines.

MULTI-PRODUCTS TANKERS Where a number of oil products are
carried, the more complex pumping arrangements require two and in some
cases three pump rooms to be fitted. One may be fitted aft adjacent to the
machinery space, a second amidships, and where a third pump room is pro-
vided this is forward. On many older tankers the piping was often arranged
on the ‘ring main’ system to provide flexibility of pumping conditions
ึ
(see Figure 26.3). To obtain the optimum number of different pumping
--- ใช้เพื่อก
combinations in modern multi-product carriers the tanks may be fitted

CARGO PUMPS Initially on modern tankers the main cargo pumps were of
the centrifugal type, either geared turbine or motor driven, and had a very
high pumping capacity, those on the large tankers being capable of dis-
3
charging say 3500m /hour. Because of their high capacities the centrifugal
cargo pumps are unsuitable for emptying tanks completely, and for this pur-
3
pose reciprocating stripping pumps with capacities of, say, 350m /hour are
provided with a separate stripping line. More recent developments have
seen the use of individual hydraulically driven submerged cargo pumps in
the cargo tanks with a single discharge line and the conventional pump
room dispensed with. Also cargo tanks are being fitted with submerged
cargo pumps driven by explosion proof electric motors. Tanker cargo dis-
charge systems are now often fully computerized.

CARGO TANK VENTILATORS The cargo tank ventilators are to be
entirely separate from air pipes from other compartments of the tanker and
positioned so that flammable vapour emissions cannot be admitted to other
spaces or areas containing any source of ignition.

CARGO TANK PROTECTION Oil tankers of less than 20 000 tonnes
deadweight are required to be fitted with a fixed deck foam system capable