This application involves pulling gases from a defined volume by pumping the tank down from a starting pressure to a final lower pressure. It is generally sized by determining the amount of time it takes to reduce the pressure in the vessel to the desired final pressure. Examples of this application would be reducing the pressure in a reaction vessel to purge it of detrimental gases, or removing steam from a vessel before opening it to increase operator safety. A variation of this type of application is the use of eductors to prime piping or a system with liquid. Priming evacuations may be used to bring the level of liquid up to pump level to avoid the pump being started dry or to establish a siphon.

Jacoby Tarbox eductor models for liquids pumping gases are: ML, MLE; for gases pumping gases: SG, HG. These models can be used for both exhausting and evacuation. See the following specifications tables for operating parameters.

Other models of eductors are available for specific applications. In some cases, these specialty eductors can pump a suction volume up to 50 times the motive volume. Most Jacoby Tarbox eductors are available in sizes from 1/2" through 3" in a wide variety of materials. Expedited deliveries are possible if needed. Units are available in sizes up to 12".

Eductors operate on the basic principles of flow dynamics. This involves taking a high pres­sure motive stream and accelerating it through a tapered nozzle to increase the velocity of the fluid. Gas motives are compressible fluids and are put through a converging-diverging nozzle. The gas can exceed the speed of sound. This fluid is then carried on through a secondary cham­ber where the friction between the molecules of it and a secondary gas (generally referred to as the suction fluid) causes this secondary gas to be pumped. These fluids are intimately mixed together and discharged from the eductor.