Throat length: In a gas jet ejector, the overall throat length (end of suction head to outside face of discharge flange) is usually between 6.5 and 8.5 X the discharge diameter. In a liquid jet eductor, it's usually 10 ft/sec or less. This helps to explain why these units are loud. Throat velocity: In a gas jet ejector, this can approach Mach 1 (1000 ft/sec) depending on the compression ratio. In a liquid jet eductor, this can be as much as 0.75 X the discharge diameter. Throat bore size: In a gas jet ejector, it is practice to limit the throat bore size to 0.5 - 0.55 X the discharge diameter. It almost always longer than a 'standard' tee of that size. The head of a liquid jet eductor is a tee 2-4 pipe sizes larger than the suction connection size. Suction head size: The head of a gas jet ejector can be (but not always is) a tee 1-2 pipe sizes larger than the suction connection size. The liquid velocity leaving it seldom exceeds 20 ft/sec. The motive nozzle for a liquid jet eductor is almost always just a 'converging' nozzle. The gas velocity leaving the nozzle can be as high as Mach 2 (~2000 ft/sec). Motive nozzle: The motive nozzle in a gas jet ejector is almost always a 'converging-diverging' nozzle. An eductor uses a liquid phase motive, usually water. Where they start to differ is in the motive fluid: Īn ejector uses a gas phase motive, usually steam or air. This balance could also be done considering momentum transfer. The mixture's kinetic energy is converted back to pressure energy. lower than the motive pressure, but higher than the suction pressure) in the throat or venturi of the device. The velocity of this mixture is then converted into an intermediate pressure (i.e. In said head (nothing more than a pipe tee really), some of the kinetic energy of the motive fluid is transferred almost instantaneously to the suction fluid until the mixture achieves a uniform velocity at the low pressure. Jetting past a suction connection in the head of the device will entrain a secondary low pressure fluid. A high pressure/ low velocity motive fluid is converted into a lower pressure/ higher velocity jet through a nozzle. What's the difference? Both are 'jet pumps' that operate in accordance with the well-known Bernoulli equation. Although the terms 'ejector' and 'eductor' are frequently interchanged, strictly speaking, they are not the same thing. Frequently, people will send us an inquiry for a 'steam jet eductor vacuum system.' This is a misnomer. Eductor (What's the 'diff' anyway?) By John Mathews, PE - Chief Applications Engineer, Croll Reynolds, Inc.

In any case, the vapours and steam going to the Vacuum System should be carefully modeled using 'vetted' computer simulation models and the eductor or ejector purchased from technically qualified 'technology suppliers'.Ejector vs. The remaining four stages might involve two steam jet ejectors and two liquid ring vacuum pumps. For example, within a deep cut vacuum distillation tower, the vacuum diesel pumparound zone at the top is not able to fully capture enough of the lower boiling components and thus the first stages of a four or five stage Vacuum System is really an Eductor compressing the as yet uncaptured condensible vapours and 'non-condensibles' and 'process steam' to a sufficient absolute pressure where these can be condensed via a 'surface condenser'. I use the term Ejector when the principal function of one or more given stages within a steam jet ejector system is 'creation of vacuum'. The diameter of the ejector's throat is lesser than the eductor.Īlan Goelzer, Jacobs Consultancy, within the context of petroleum refining and non-conventional oil upgrading, I use the term Eductor when the principal function of a given stage within one-to-five stage steam jet ejector system becomes 'compression of vapours or gases'. The difference is with respect to their function and not with respect with their motive fluid. whereas the ejectors just suck the excess volume of the system and maintains the system pressure accurately. Hence the Eductors can be used to transfer a considerable volume of fluid from low pressure to high pressure with high compression ratio than ejectors. Here the motive fluid is high pressure water. The water jet eductors are used to suck the muddy water, or a oily water from the storm water channel or a pit (an alternative for a de-watering pump). The eductors are used to remove the air 4 times the volume of the vessel per hour for the vessel entry jobs. GS Singh, NPCC, ejectors are used to maintain a system vacuum in the upstream (Example maintaining the vacuum column pressure) whereas eductor's main objective is to take out the volume of any fluid out of the system by maintaining a system pressure in the upstream.

Eductor vs ejector