Eductors for Pumping Gases- Jet Pumps
This application involves pulling gases (using jet pumps) 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 jet pumps 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.
Download Eductors Liquids-Gases Pulling Gas Brochure - PDF
| Model | ML / MLE | SG | HG |
| Motive Media | Liquid, Liquid | Steam, Air | Steam, Air |
| Motive Pressure (PSIG) | 20-250 20-250 | 60-120 | 20-80 |
| Max. Vacuum (in Hg) | 29 / 29 | 24 | 24 |
| Outlet Pressure (PSIG) | 20 /20 | 12 | 20 |
There are three connections common to all venturi eductors.
(1) Eductor MOTIVE Connection: This connection is where the power for the eductor is generated, by increasing the velocity of the motive fluid. The Jacoby-Tarbox eductor nozzle in this section takes advantage of the physical properties of the motive fluid. Eductors with liquid motives use a converging nozzle as liquids are not generally compressible. Eductors with gas motives utilize converging-diverging nozzles to achieve maximum benefit from the compressibility of the gas. All Jacoby-Tarbox eductor nozzles for eductors have smooth flow paths. Flow paths with sudden steps or roughness on these high velocity surfaces cause jet pumps to operate less efficiently.
(2) SUCTION Connection: This connection of the eductor is where the pumping action of the eductor takes place. The motive fluid passes through the suction chamber, entraining the suction fluid as it passes. The friction between the fluids causes the chamber to be evacuated. This allows pressure in the suction vessel to push additional fluid into the suction connection of the jet pump. The high velocity of the motive stream in this section of the eductor directs the combined fluids toward the outlet section of the eductor.
(3) Discharge Connection: As the motive fluid entrains the suction fluid, part of the kinetic energy of the motive fluid is imparted to the suction fluid. This allows the resulting mixture to discharge at an intermediate pressure. The percentage of the motive pressure that can be recovered is dependent upon the ratio of motive flow to suction flow and the amount of suction pressure pulled on the suction port. The mixture then passes through the diverging taper that converts the kinetic energy back to pressure. The combined fluid then leaves the outlet.