A flexible arrangement

For example, a Gdynia contract mounted the unloader on a gantry with the land side end supported by the silo immediately behind the quay. Discharge to the machinery house is pneumatic, while horizontal transfer to the silo is via a chain conveyor fitted to the top of the gantry.

And a Vigan unit in Algeria has been used by being lifted directly on to ship decks next to the hold, sucking grain out at some 250 tonnes per hour with a belt conveyor loading the trucks on the jetty.

Relatively small operations on large tidal flows can also find pneumatic units an advantage. For example, Vigan’s Alain de Visscher says that some small ports in Africa have such exposed conditions that they rely on the physical flexibility of the vacuum unloaders. A mechanical unit, with its rigid marine leg, has to rely on a very quick response from the angle of the support jib to accommodate swells.

“If the ship is moving, not only can damage occur to the hold, but more importantly from the stevedore’s viewpoint, the feeder head can be damaged,” he explains.

The pneumatic machines can have telescopic extensions or ones fabricated from reinforced rubber tubing to accommodate loading contact. Even so, there are other options.

At river terminals (where water levels can fluctuate as much as 30′), FLSmidth has installed machines on barges or floating docks so the unit keeps abreast of the discharging vessel. “If the machine’s platform was on the shore or a fixed dock, it would mean having to design a completely different type of vacuum arm (e.g. a telescopic chute), which would impair the machine’s performance without significantly higher cost or power consumption,” explains Mr Bergenstock.