Jet Pumps Information
Jet pumps, also known as ejector pumps, are devices capable of handling and transporting all forms of motive fluid including gas, steam, or liquid. They can be considered mixers or circulators, since the intake combines multiple fluid sources. Multiple inlets are used to draw in a constant stream of fluid, using pressure to create lift through suction. The combination of intake pressure and velocity of the liquid or gas jets the media up from a well, tank, or pit through the pump to the discharge point.
Jet pumps are less efficient than typical centrifugal pumps due to such factors as friction loss, but may be more efficient when working with combined media that includes gases, and in variable well conditions where the surface characteristics involve turbulence.
Jet pumps are centrifugal pumps with an ejector (venturi nozzle) attached at the discharge outlet. They function based upon the Venturi effect of Bernoulli's principle - utilizing constriction to reduce pressure and provide suction. After the pump is primed, a motive fluid is pumped through a standard centrifugal pump and enters an ejector. At the throat of the converging section of the ejector, the pressurized fluid is ejected at high velocity. This creates a low pressure (vacuum) at the throat, drawing the target fluid (from a well or other source) up into the nozzle. This picture is a diagram of the ejector portion of a jet pump:
Image Credit: Mbeychok (Wikipedia)
This video provides visual explanation of a jet a pump's operation:
Video Credit: iecSimulations
Jet pumps consist of three sections: a centrifugal pump, a jet ejector package, and a foot valve.
The centrifugal pump generates the force which circulates the motive fluid through the ejector, typically using an impeller powered by a motor. For more information on different types of centrifugal pumps, visit How to Select Centrifugal Pumps on Engineering360.
The jet ejector package (the nozzle, venturi, and various connections) is often separate from the pump before installation. Ejector components are carefully engineered to match the flow rate of a specific pump. During installation, it is important to read the ejector package instructions and set the package up correctly for the specific horsepower of the pump.
The foot valve is the section connected to the well or target resevoir. It receives fluid into the system and feeds the pump, filters debris and sediment from entering the system, and maintains the pump prime, preventing backflow.
Jet pump system, indicating its various components. Image Credit: National Resources Management and Environmental Department
There are four main types of jet pumps, which vary based on application and size.
Deep well jet pumps are used in high volume applications, such as oil wells, which range from 800-15,000 feet in depth. The ejectors in these pumps are put down the well.
Shallow well pumps are used in applications where the media is close to the surface, such as residential wells. The ejectors in these pumps are bolted to the nose of the pump.
Convertible jet pumps are "convertible", meaning they can be set up to be used for either deep or shallow well applications.
Miniature jet pumps are used for smaller (typically commercial) applications, such as aquariums.
The primary specifications to consider when selecting jet pumps are flowrate, pump head, pressure, horsepower, power rating, outlet diameter, and operating temperature. Engineering360's Pump Flow page describes these performance specifications in detail. One important consideration specific to jet pumps is this: if external pressures and internal pressures exceed the material specifications and the pressure specifications of the jet pump, the throat of the pump can collapse and cause damage or extreme reductions in flow.
Housing materials for jet pumps include plastics, steel alloys, and cast iron.
Plastics, including polypropylene (PP), polyvinyl chloride (PVC), acrylic, and polytetrafluoroethylene (PTFE), are less expensive and provide resistance to corrosion and a broad range of chemicals.
Steel alloys, including stainless steel, are stronger and more abrasion resistant than plastics and provide good corrosion and chemical resistance.
Cast iron provides high strength and abrasion resistance.
For more on materials and other pump features, visit Engineering360's Pump Features page.
Jet pumps are typically inserted vertically into the process media, but can be mounted horizontally as well. They are often used in applications where the material that is pumped assists in creating the motive force needed to move through the pump. For example, in marine applications, jet pumps are used to transfer seawater. In home applications, they are used to move wastewater up to the sewer line. A float level sensor and switch are used to turn on the pump.
Engineering360's Pump Applications page provides an overview of pump types used for specific applications.
Image Credit: Griffin Pump & Equipment Inc. | Watts