How Does an Eductor (Jet Pump) Work ?
An eductor, also known as a jet pump or Venturi pump, operates on the principles of fluid dynamics to move or mix liquids, gases, or even solids. It achieves this by converting the pressure energy of a “motive fluid” into velocity energy.
Here’s a step-by-step explanation of how it works:
- Motive Fluid Input: A high-pressure “motive fluid” (which can be a liquid like water or steam, or even a gas like air) is introduced into the eductor.
- Nozzle Acceleration: This motive fluid is then forced through a converging nozzle. As the fluid passes through this narrowing section, its velocity significantly increases. For gas motives, a converging-diverging nozzle is used, and the gas can even exceed the speed of sound.
- Pressure Drop (Venturi Effect): The rapid increase in velocity results in a substantial decrease in pressure within a “suction chamber” or secondary chamber, creating a partial vacuum.
- Suction of Secondary Material: This low-pressure zone draws in a “secondary fluid” or “suction material” through a separate inlet port.
- Mixing and Discharge: The motive fluid and the suctioned material then intimately mix together in a “throat” section. This mixture is then expelled through a diverging section (diffuser) at a pressure higher than the suction stream but lower than the initial motive pressure.
Essentially, an eductor leverages the energy of one fluid stream to create suction, thereby pumping or mixing another substance without the need for any moving parts. This design contributes to their simplicity, reliability, and low maintenance.
Eductors are a kind of jet-type pump that do not require any moving parts to be able to pump out a liquid or gas. These pumps make use of their structure to transfer energy from one fluid to another via the Venturi effect. The structure of the pump is such that it has an injector chamber with a narrow shaped nozzle or tapered jet that is located inside the chamber and points axially towards the exhaust chamber to increase the pressure of the motive fluid as it enters the eductor. At the bottom of this nozzle is an opening that is used to suck in any form of fluid or other substance that needs to be extracted from a certain environment. The suction happens due to Venturi effect that creates a drop in pressure at the tip of the nozzle due to the fast flowing motive fluid which has gained kinetic energy due to the tapered shape of the nozzle. This difference in pressure causes the desired fluid to be sucked into the eductor and mixed into the flow stream to be guided out of the eductor.
What’s the purpose of an eductor?
The primary purpose of an eductor is to move or mix liquids, gases, or even solids without any moving parts. They achieve this by utilizing the fluid flow of a “motive fluid” to create suction and transport another substance.
Eductors are used in a wide range of applications, including:
- Pumping: They can pump fluids from one location to another, even if they are at different pressures.
- Mixing: Eductors can mix two or more fluids, or liquids and solids.
- Transporting solids: They can transport solids like sand or gravel in a liquid stream.
- Creating a vacuum: Eductors can be used to create a vacuum for tasks such as evacuating tanks or degassing fluids.
- Heating: Tank eductors can be used for practical, simple, and cost-effective heating in an open tank, such as cooking grain or heating and circulating.
Their benefits include their simple design, reliability, low maintenance, and versatility.
These pumps are able to carry out dewatering in circumstances where other pumps might not be able to function and that too at a very fast rate. Liquids that cannot be pumped using other pumps can be extracted through eductors such as liquid that may contain particles of solid or foreign matter. The portability of these pumps allows them to be used in various applications. However, an important thing to note would be that not all of the fluid that an eductor discharges comes from the compartment that is being dewatered. As the eductor may be activated by water and also by extracting water, only a certain portion of its discharge would be the distracted water as the motive fluid would have mixed with it and discharged through the exhaust. Another important thing to note is that the pressure of the motive fluid that is supplied to extract another fluid from a certain area should always be higher as compared to the fluid that has to be extracted. If this is not the case, the eductor would instead simply end up flooding the area, instead of distracting any fluid or substance.
Before and while utilizing these pumps, the user should ensure that the pressure of the motive fluid is higher than the fluid to be extracted; the hoses should be free of kinks, the eductor should only be charged with a motive fluid when it is fully submerged in the fluid to be extracted and keep the eductor submerged while the fluid is being extracted.
Eductors have several advantages over other types of pumps that may use electricity or fuel to pump out water. Also the fact that these pumps are portable makes them very much versatile and usable in applications where other pumps may prove useless.
The Venturi theory, or Venturi effect, describes how the speed of a fluid (liquid or gas) increases as it flows through a constricted section of a pipe or tube, simultaneously causing the fluid’s pressure to decrease.
Here’s a breakdown of the key principles:
- Conservation of Mass (Continuity Equation): For an incompressible fluid, if the cross-sectional area of a pipe decreases, the fluid must speed up to maintain a constant flow rate. Imagine a river: where it narrows, the water flows faster.
- Bernoulli’s Principle: This fundamental principle of fluid dynamics states that for a steady flow of an incompressible, non-viscous fluid, an increase in the fluid’s speed occurs simultaneously with a decrease in its static pressure or a decrease in the fluid’s potential energy. In a Venturi, as the fluid accelerates in the narrowed section, its kinetic energy increases. To conserve the total energy, its static pressure energy must decrease.
How it applies in an eductor/Venturi pump:
In an eductor, a high-pressure “motive fluid” is forced through a converging nozzle. This nozzle’s narrowing passage causes the motive fluid to accelerate significantly. According to the Venturi effect (and Bernoulli’s Principle), this increase in velocity results in a substantial drop in the fluid’s pressure, creating a low-pressure zone or partial vacuum in the suction chamber. This vacuum then draws in a secondary fluid or material, which is then mixed and discharged.