An eductor is the name of a pump that uses the venturi effect during a pumping operation. This is a type of jet pump which is used to pump sediment and liquid out. They’re often used when the suction head is too deep for another pump.
Due to the Bernoulli principle and venturi effect, the primary fluid used creates a vacuum for air, liquid, or gas to be sucked into. Thanks to the simple design and construction, it can be used on ships, or hazardous areas, and in any industry that needs to extract large amounts of debris.
In this article, we will go into further detail into what is eductor is and how it works.
What Is An Eductor?
As we have established above, an eductor is a type of pump which can be used to remove large volumes of debris in certain areas. It has a very simple design that uses no moving parts, which makes it ideal to be used on a ship.
An eductor contains a suction chamber, a suction and discharge point, and a nozzle input. This is where high-pressure and low-velocity fluid is converted to low-pressure and high-velocity fluid. This difference in pressure is what causes the suction to occur.
There are many advantages to using an eductor pump, as it is a unique piece of equipment. It is low in price, self primed, and uses no moving parts. Also, it uses such a simple design, it can be used in hazardous areas and it is easy to control.
This is important when it is used in any areas that have fluids that can cause explosions, as well as in emergencies when ease of use is paramount.
The suction chamber of the Eductor depends on the driving fluid and its flow rate. The nozzle diameter will rely on the motive fluid pressure, suction requirement, and pressure drop.
The Advantage Of An Eductor Pump Over Regular Pumps
It is clear that there are some distinct advantages of having and using an eductor pump over a regular pump in particular situations.
The main reason why an eductor pump will be used over a regular pump is due to its low running costs and the ability to allow vacuum pump assisted operations. It is known that you can manage around 150 eductor pumps at one time with various vacuum conditions.
An eductor pump is seen as a very useful piece of equipment in sumps, tanks, and deep wells during stripping operations. It is also useful that this pump doesn’t have any vacuum limits.
This means it can be used to work with a medium that contains solid or metal contaminants. These would cause damage to a regular pump.
Alongside that, it doesn’t need electricity or a prime mover to make it work and is very suited for low to very high viscous fluids.
Due to this reason, the eductor pump is often used when it comes to soil stabilization. It is also used for cleaning operations, choked drainage systems, and drilling operations. There are also a range of other site operations it could be used for, but those are the most common ones.
What Causes The Suction In A Eductor Pump?
To answer the question of how does an eductor work is relatively simple by stating that eductor uses the Bernoulli principle. This principle explains that the speed of the fluid in a suction chamber will increase as the pressure of the fluid will simultaneously decrease. This is often used to explain mechanical energy conservation.
The change is always constant, and with this increase in pressure comes a decrease in velocity. Now we know that fluid will flow at a specific and constant rate, due to the continuity equation, which is as follows:
P1 V1 A1 = P2 V2 A2 = P3 V3 A3
The amount of fluid that is flowing through the pipe will depend on the cross-section area (Q = A x V) and the velocity. This is where we get the following equation:
P1= P3, V1 = V3, and A1 = A3
Hence, within the pump, A1 is seen as greater than A2. However, V1 is lesser than V2. Therefore, if we use the venturi effect, the end result we get is P2 < Patm < P1.
This is due to the fact that the increase of pressure within the suction chamber of the pump is lesser than the pressure in the atmosphere. Hence, the secondary pressure is pushed into the suction chamber, which then produces the pumping action that is desired.
Also, the tip of the nozzle will convert low-pressure high-velocity fluid to high-pressure low-velocity fluid and vice versa. It is during this process that the pressure inside the suction chamber and the outside atmosphere pressure create the vacuum which then causes the pump to begin, well… pumping.
Assembly And Construction Feature Of An Eductor Pump
An eductor pump is created using a simple and easy construction. It uses a body made from alloy, cast or stainless steel, a suction chamber and line, discharge, Gasket O-ring, diffuser, motive fluid nozzle, screw, and a converging inlet nozzle.
For the assembly of this pump, inside the suction chamber, a nozzle or tapered jet is found. This tapered jet allows any fluids to be able to leave the chamber towards the diffuser outlet or the exit.
Then below the nozzle, you will find the suction pipe. This pipe will suck any kind of fluid which needs to be pumped or extracted from any system.
Then the flow side is joined to the driving fluid or the motive. Therefore, due to a continuous flow of the driving fluid, this is when the venturi effect begins to start. Next, due to the suction that is formed, the driving fluid is sent to the diffuser outlet. This allows for the pump to remain efficient.
What Is The Difference Between An Ejector Pump And An Eductor Pump?
An eductor pump will use liquid or water as its motive or driving fluid. It typically has quite a big suction head with a motive fluid nozzle that is a converging type.
Overall, an eductor pump has a low operating velocity of around 10 seconds/ft for motive liquid, with no maximum bore size. Finally, an eductor pump is seen as a silent pump that makes virtually no noise when in use, with a high compression ratio.
While on the other hand, an ejector pump will use air or steam instead of a liquid as its motive for draining fluid. They also use a different type of motive fluid nozzle, which is a converging-diverging type with a small suction head.
An ejector pump uses a high operating velocity of 1000 seconds/ft for driving fluid. Alongside this, the ejector pump is still quiet, but when compared to the eductor, it isn’t as silent and does make a slight noise.
There are lots of differences between the two, yet the eductor comes out on top. It is easier to use and makes much less noise and isn’t as limited as the ejector pump.
Uses Of A Eductor Pump
You can see the eductor pump used in a range of different industries, especially when they would like to use a much lower cost alternative to centrifugal pumps.
Often these pumps are used for a range of pumping operations or when it comes to handling solid waste in slurries. Due to creating a vacuum, they can remove different liquids and even some solids with ease.
On a ship, an eductor pump will be used as the stripping or priming pump or in vacuum toilets. Eductor in a ship can be used for a wide range of different pumping needs. For example, eductor systems are commonly used in a ballast tank system as a ballast remaining water stripping pump when the main ballast pump is not able to pump the remaining small amounts of the ballast water.
Conclusion
Eductors are very useful and versatile pumps that have been around since the early 1900s. They are a great way to handle solids and liquids at the same time. With a simple but effective construction, these contraptions are trusted by many industries.
We hope this article has helped you to understand what an eductor pump is and how it works.
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