What is Eductor-Jet Pumps?

Eductor-jet pumps are pumps that have no moving parts but use only a pressurized fluid to pump another fluid. Eductor-jet pumps also result in the effective mixing of these two streams. Although the concept is simple, there are many applications of these pumps. One of the most common is chemical addition, such as the fire-fighting foam eductor-jet pump, which adds foam to the water stream.

This article will discuss the principles of operation and the different applications of variations of an eductor-jet pump.

What Is an Eductor-Jet Pump?

An eductor-jet pump is a simple device that has no moving parts but uses the pressure energy from one fluid to pump another fluid. The low pressure created between the nozzle and diffuser draws in another fluid. This simple pump can be installed without electrical power and has very low maintenance requirements as it has no moving parts. However, it is still versatile, as variations of eductor-jet pumps are used for boreholes, tank blending, chemical addition, and hydraulic solids transport.

What Are the Basic Principles and Design of an Eductor-Jet Pump?

The basic principle of an eductor-jet pump is to accelerate a fluid through a nozzle to create a suction to draw in another fluid to be pumped. The design of an eductor-jet pump incorporates three key elements as explained below:

Converging Nozzle: A pressurized fluid is driven through a converging nozzle. The convergence forces the fluid to accelerate, and this creates a low pressure. This nozzle is often removable from the eductor-jet pump and can be replaced if necessary. Its sizing affects some of the characteristics of the pump.
Diffuser: The accelerated fluid is expanded through a diffuser, regaining some of its pressure. This diffuser typically has a venturi shape.
Body: The body of the eductor-jet pump holds the different components together. It also incorporates the suction inlet (or inlets) to direct the fluid to be pumped into the low-pressure gap between the nozzle outlet and the diffuser inlet.

How Does the Eductor-Jet Pump Work?

The eductor-jet pump works by using a high-pressure fluid to move a low-pressure fluid. The high-pressure fluid is ejected through a nozzle as a jet, and directed into a diffuser. This diffuser can also be referred to as a venturi or a throat. The movement of the jet through the diffuser causes a low pressure to form, which then creates a suction. This draws in the second fluid and causes it to flow together with the jet through the diffuser. In this way, the two fluids mix in the diffuser, and leave the diffuser at a pressure between the starting pressures of the two fluids.

What Are Different Variations of Eductor-Jet Pumps?

Although all eductor-jet pumps operate on the same principle, there are several different variations to suit different applications:

Central Jet Pump: This is the simplest design of an eductor-jet pump, with a single nozzle located centrally to the diffuser and body.
Tank Mixing: This eductor-jet pump has a modified body that allows inlet flow from all sides, as it is submerged within a tank.
Multi-Nozzle: These eductor-jet pumps have multiple nozzles arranged around a circular body. Using multiple nozzles allows the diffuser to be shortened, making some difficult installations possible.
Lift Jet Pump: This has a body that receives pressurized flow in one direction and directs exit flow in that same direction. These are installed vertically, in locations such as the bottom of boreholes, in which they receive pressurized flow from above (ground level) and direct the water flow back up out of the borehole. This design can also be used for emptying the slurry of a pit.
Dosing Pumps: These eductor-jet pumps have suctions designed for small chemical dosing flows, such as for chlorine gas in water treatment, or foam in fire-fighting applications.

In Which Industries Are Eductor-Jet Pumps Most Commonly Found?

Eductor-jet pumps are naturally common in certain industries. One of these is in water and wastewater treatment. Water is a common motive fluid for eductor-jet pumps, and so they are used widely. They are used for dosing water-treatment chemicals, such as chlorine gas for disinfection. In the USA, they are also used for shallow borehole pumps to produce raw water from boreholes for treatment. Jet aerators are also used in wastewater treatment, in which the eductor-jet pump sucks air in from above the water surface to inject it below.

Similarly, eductor-jet pumps can be used in the oil & gas industry. They are widely used for chemical injection for well treatment. The benefit of eductor-jet pumps for chemical injection is that they also provide effective mixing of the additive into the bulk. They can also be used at the bottom of a well for well-stimulation.

Another common industry that uses eductor-jet pumps is the chemical processing industry. Particularly for solid granular raw materials, they are used for transport. They are also used for tank mixing and blending, as well as introducing additives.

What Are the Benefits of Eductor-Jet Pumps Compared to Other Pumping Methods?

Eductor-jet pumps have multiple benefits when compared to other types of pumps, such as:

There are no moving parts at all in the body of the pump. This means that the risk of failure is much lower than other pumping methods, which typically have rotating impellers, moving gears, or reciprocating pistons.
An eductor-jet pump uses only a pressurized fluid for pumping energy. No electrical connection is required at all, making it much simpler to install in more remote locations.
Due to not needing electricity, and having a simple construction without moving parts, the installation cost of an eductor-jet pump is lower than most other types of pumps.
The eductor-jet pump creates a suction and therefore is self-priming. This eliminates a complication that some other pumps have — that they need to be primed if situated above the normal liquid level.
What Are the Drawbacks Associated With Eductor-Jet Pumps?
Eductor-jet pumps are fantastic pieces of equipment for the right application, but there are still some drawbacks that should be considered when comparing them to other pump types. Drawbacks include:

Eductor-jet pumps have a low pumping efficiency. When compared to other types of pumps, more energy is required (via the pressurized fluid) for pumping a unit volume of the pumped fluid. Maximum efficiency from an eductor-jet pump is less than 40% and can be practically less than 30%.
Eductor-jet pumps are not able to pump large volumes relative to their size. Further to this, the pressurized fluid injection flow rate can be as much as twice the pumped fluid flow rate. This means that the pumping flow is only a portion of the flow that the eductor-jet pump can handle.
How Does the Cost, Efficiency, and Maintenance Stack Up Against Other Pump Types?
Eductor-jet pumps stand out as quite different compared to other types of pumps. In terms of installed costs, particularly for smaller flow rates and in more remote areas, eductor-jet pumps are significantly cheaper than other types of pumps (provided the pressurized fluid is already available). This is because they do not need any electrical power connection. Further, their maintenance costs are very low compared to other types of pumps because they have no moving parts. An inspection and potentially some cleaning may be all the maintenance required for years of operation (providing the fluids are not abrasive). However, the trade-off for these benefits is that the efficiency of eductor-jet pumps is significantly lower than that of most other pump types. The energy lost from the pressurized, motive fluid pumps a relatively small volume of low-pressure fluid. The maximum theoretical efficiency from an eductor-jet pump is less than 40%, but practically they often operate at efficiencies below 30%.

What Should You Consider When Installing an Eductor-Jet Pump?

When installing an eductor-jet pump, there are several aspects to consider. The first is the accessibility of the pump for maintenance. Although eductor-jet pumps require very little maintenance, it is valuable to have reasonably easy access to inspect and clean the pump when necessary. Therefore, even if it is installed in an inaccessible place (such as a borehole), arrangements should be made for how the pump will be retrieved.

Performance monitoring and troubleshooting should also be considered. This may be allowed for by installing upstream and downstream pressure gauges and flow meters. These will provide the necessary information to assess the performance of the eductor-jet pump and provide a quick identification if there is a partial failure or blockage of the pump. In some applications, the suction lift may be particularly critical. This could also be monitored if necessary.

The piping layout to and from the eductor-jet pump is also an important consideration during installation. As far as possible, the piping should have minimal bends and fittings to reduce pressure losses through the piping. Particularly when using the pump for the transport of granular solids, low spots, and sharp bends should be avoided to prevent choking with solids.

What Are Real-World Applications of Eductor-Jet Pumps?

There are many real-world applications of eductor-jet pumps, such as these below:

Dosing and Chemical Addition: Eductor-jet pumps are commonly used with water as the motive fluid, to add a chemical to the water stream. A real-world example of this is fire-fighting foam, which is stored in drums but applied to a fire via an eductor-jet pump when water is pumped through it and sprayed on the fire.
Solids Transport: Placing an eductor-jet pump below a hopper of granular material allows the solids to be transported hydraulically. This is applied in processes to transport building materials like sand or stone. Some of the motive water is bled off into the hopper as a wash-down to increase the capacity of the eductor-jet pump. This helps to prevent air from being entrained by the eductor-jet pump and also keeps the solids flowing into the suction.
Tank Blending: Eductor-jet pumps can be placed in a tank and paired with an external recirculation pump. The external recirculation pump continuously supplies the jet with pressurized flow, which then in turn sucks in the bulk tank contents and mixes it vigorously through the eductor. In this way, effective blending is achieved with no moving parts within the tank.
What Are Misconceptions About Eductor-Jet Pumps?
Some misconceptions and misunderstandings about the application of eductor-jet pumps include:

The many different names that are used to refer to eductor-jet pumps can often cause some confusion. They can be referred to as: injectors, eductors, jet pumps, venturi pumps, or even siphon pumps.
A misconception about eductor-jet pumps can be that they have limited areas of application, or are only suitable for one type of service. The reality is that the different variations of eductor-jet pumps allow them to be used in a wide range of applications, such as: boreholes, solids transport, tank mixing, chemical dosing, and vacuum creation. These cover a wide range of industries, from mining to plastic molding and water extraction.
It may be thought that it is complex to design an eductor-jet pump. However, the factors at play are simple enough that finding the right pump for a specific set of parameters is not very difficult to do.
What Factors Should Be Considered When Selecting an Eductor-Jet Pump for a Particular Need?
Several factors should be taken into account when selecting an eductor-jet pump for an application, such as:

The desired flow rate of the fluid to be pumped is a crucial factor in the sizing of the necessary eductor-jet pump.
The discharge pressure of the combined fluid is necessary for selecting the flow and pressure of the motive fluid, as well as the nozzle and throat of the eductor-jet pump.
It is important to know whether the eductor-jet pump is required to handle solids, and if so, the maximum size of solids and the acceptable solids percentage in the combined flow.
Materials must always be selected according to their chemical compatibility with the fluids passing through the eductor-jet pump. This may also need to consider abrasion resistance for some types of solids.
Can Eductor-Jet Pumps Be Used for Molding Applications?
Yes, an eductor-jet pump can be used for molding applications. Its primary use in plastic molding applications is to transport and mix the granular solids that will be melted down before entering the mold. An eductor-jet pump is a simple and low-cost way to transport non-abrasive solids from a hopper. By using a pressurized fluid through the eductor-jet beneath the hopper, the solid granules of plastic are entrained in the fluid, which generates a mixed and homogenous two-phase flow to the plastic granules’ destination — at the plastic molding equipment.

What Molding Processes Can an Eductor-Jet Pump Be Used In?

Various types of molding processes can use eductor-jet pumps, including injection molding, extrusion molding, and blow molding. The pumps are primarily used to transport and mix granular plastic materials. Eductor-jet pumps can also be used to provide mixing within tanks, with no moving parts or external power. The eductor-jet suction is open to the tank at large, with the outlet jet directed within the same tank. In this way, a homogenous molten plastic mixture can be created.

What Is the Difference Between an Eductor-Jet Pump and an IMO Pump?

There are multiple differences between an eductor-jet pump and an IMO pump. IMO pumps are positive displacement pumps that use three intermeshing screws to pump fluid. These are fundamentally different from eductor-jet pumps — there are multiple moving parts with small tolerances between them, an electrical power supply is necessary, and the fluid is physically forced through the pump by the rotors (positive displacement) rather than using pressure dynamics. As a result, the application of IMO pumps is also very different — they are typically used for high-pressure delivery of oil or water, or in polymer manufacturing for pumping materials such as nylon and isocyanate.

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