The most common use of an eductor is in tank cleaning operations including COW operations and the required capacity is often determined by this operation. They are increasingly being used for clean ballast and stripping duty.
To strip efficiently, an eductor used for tank cleaning operations should have a capacity of about twice the rate of liquid being introduced to the tanks.
Eductors are always to be operated at or near their design driving pressure as, in general, lower driving pressures will considerably reduce eductor efficiency. Higher back pressures in the system than the eductor was designed for can also reduce suction capacity.
The eductor drive liquid must always be flowing before the suction valve is opened to prevent back flow of the driving liquid to the tank suction.
When shutting down an eductor the suction valve is to remain open until the eductor is stopped to prevent the eductor drawing a vacuum on the suction line.
If, during use, the eductor driving pressure falls below the required operating pressure, the eductor suction valve is to be closed to prevent backflow of the driving liquid. The tank suction must not be used to prevent backflow as the suction pipe work is not designed for such high operating pressures.
When stripping cargo tanks with an eductor, the recovered liquid is to be collected in a slop tank before final discharge ashore with a cargo pump. In general the discharge head on a shore line will not permit direct discharge to the shore using an eductor.