Operating mechanisms
After careful consideration it has been decided
to operate the gates by hydraulic cylinders.
These are manufactured in seven sizes. The
longest make a stroke of 13,2 m. Some ofthe
components are already preprocessed, whereas
other parts are rolled and welded in Holland.
The weldings are checked in three ways. The
final assembly into complete cylinders is also
carried out in Holland. Internal and external
drilling - in which great precision has been
achieved - and filing to a smoothness of 0,4
microns perfects the cylinders.
The forged steel piston rods of the operating
mechanism should have optimum protection
against the aggressive climatic conditions to
which they are exposed. They are plated with
nickel and chrome according to an electrolytic
procedure. The diameter of the rod is compared
before and after the procedure in order to
check that the protective layers have acquired
the proper thickness. There is a fixed maximum
of permissible imperfection in the final surface.
The hydraulic cylinders are hinged in two
directions to the piers of the storm-surge
barrier with the assistance of cardan beams.
Although they go with seven different cylinder
types they only need be manufactured in four
different versions. The cardan beams are
welded constructions, built with sheets of
various thicknesses.
Two aspects in the assembling together of the
cylinders, the pistons and the cardan beams
require special attention. The components
must be kept absolutely clean and the elastic
deformations caused by their own weight must
be taken into account. All sorts of helpful
constructions have been thought out for this
purpose. After the components have been
telescoped into each other and the lids have
been closed, oil is pumped into the system and
a number of tests are carried out for smooth
working and hydraulic compactness. It is only
after all this that the lower eye is attached to
the piston and a conservation chamber is
added. Assembly with the cardan beam follows
later.
Eight operating mechanisms together are
crossed over to the Oosterschelde barrier by a
pontoon adapted for this purpose, and are
mounted onto the pier in pairs by the trestle
'Taklift IV'.
Hydraulic systems
Each cylinder has its own pump apparatus.
Two pumps placed next to each other on the
pier serve two cylinders and also act as each
others reserve. The pumps and electrical
equipment are built-in in containers which are
placed in the road box girders before these
form part of the barrier. Each container is
tested individually beforehand. In addition to
this one of the electrical systems was tested in
full operation, connected to four hydraulic
aggregates.
The building of the containers, which serve as
machine rooms, high voltage rooms, for
switchboards, workshops and offices has been
standardised as much as possible.
The great advantage of the containers is that
the assembly of electrical and hydraulic
equipment no longer depends on the
completion of the storm surge barrier, and that
the installations are well protected against
disadvantageous weather conditions.
Gate Control
The permissible chance of failure in the gate
control and the leveling gear has been fixed at
103 per year, which is an extremely high
standard of reliability. The relevant data for
each gate are gathered with the assistance of
three independent digitalizers. The local
computer makes three calculations and then
takes a majority decision whose execution is
checked by yet another computer. A data-net
connects the local installations with the central
computer in the service building. Here the
position of the gates and the state of the
equipment can be read from a screen. From
here orders can also be conveyed to the local
installations, which is done according to the
'safe' and the 'alternative' methods of operation.
Besides this five different, independent
communication systems have been placed so
as to be able to communicate within the entire
complex. Energy for the barrier while it is not
actually working will be drawn from the public
network. A separate power station will be built
foroperational use, using parts ofthe temporary
diesel station on Neeltje Jans.
Safeguarding devices against lightning
The Oosterschelde barrier is a high construction
in a flat landscape. The cylinders of the lift
structure tower above the barrier. It may be
reckoned that lightning will strike about twice a
year. The lightning will seek the shortest route
to earth, via the steel re-inforcement of the
barrier. Insulation fitted between the steel parts
on the barrier and the piers could short circuit.
The micro-processors in the electric containers
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