The motive medium drives the ejector. This medium is always injected in the ejector at higher pressure than atmosphere. Several different mediums can be used as motive mediums. The most common are water and air.
Basically, the ejector can be motivated by any medium up to a certain viscosity level.
Water is the most efficient medium to drive the ejector.
Air can be a preferable medium to use when pumping gasses.
Many other applications exist for ejectors, where a liquid (or slurry) needs to be pumped or a vacuum created using either liquid or gas as the motive source. There is one exception, though; pumping of liquid using compressed gas will usually be too inefficient to be of practical use.
Small particles: include mediums such as sand, powder and coal powder.
Sewage: is characterised by a combination of water and slurry, this includes all sorts of sewage water and bilge.
Fuel and oil: an ejector eliminates explosive risk during transferring and stripping of all types of fuel and all types of oil
Water: for removal of any type of water from e.g. ballast tanks, cargo tanks
Gas: for emptying of gasses from ballast tanks or other tanks. The ejector has no moving part, which eliminates explosive risks.
Smoke: ejectors can be used for ventilating and suction of smoke, this can be relevant in the engine rooms.
Air/vacuum: for priming of centrifugal pumps or other vacuum purposes.