This is a closed design of an eductor that allows the system to be used to draw materials in the hopper. The eductor can mix water and sand, air and sand, water and air etc. There are many combinations that this will work with.
Eductors are generally used to pump large volumes of coarse material. They are ideal for this as there are no moving parts within the eductor. They are also used readily on marine/fish tanks to aerate the water and keep teh water flowing.