An eductor-jet pump or jet pump is a type of pump where the energy from one fluid (liquid or gas) is transferred to another fluid via the Venturi effect. As the fluid passes through a tapered jet, kinetic energy increases and pressure decreases drawing fluid from the suction into the flow stream.
Jet pumps can be used for draining areas which may contain combustible fluids (which could ignite if exposed to the workings of a standard electric or internal combustion powered pump) or high levels of debris (for example water eductor) which could damage screws or blades in conventional pump designs.
Jet Pump Description
A source of pressurized fluid (e.g. a firehose) is connected to a injector chamber which is open on one end, and leads to an exhaust hose on the other end. The pressurized fluid is forced through tapered nozzles (called eductor jets) mounted axially on the inside of the pump chamber, pointed in the direction of the exhaust hose. The passage of the pressurized fluid through the chamber and into the exhaust hose creates a suction on the open end of the chamber (see Venturi effect), such that any fluid the pump chamber has been submerged in will be drawn into the chamber and thence into the exhaust hose along with the fluid from the eductor jet nozzles.
There are three connections common to all jet pumps.
Jet pumps are commonly used to extract water from water wells. A powered pump, often a centrifugal pump, is installed at ground level. Its discharge is split, with the greater part of the flow leaving the system, while a portion of the flow is returned to the jet pump installed below ground in the well. This recirculated part of the pumped fluid is used to power the jet. At the jet pump, the high-energy, low-mass returned flow drives more fluid from the well, becoming a low-energy, high-mass flow which is then piped to the inlet of the main pump.
Shallow well pumps are those in which the jet assembly is attached directly to the main pump and are limited to a depth of approximately 5-8m to prevent cavitation.
Deep well pumps are those in which the jet is located at the bottom of the well. The maximum depth for deep well pumps is determined by the inside diameter of and the velocity through the jet. The major advantage of jet pumps for deep well installations is the ability to situate all mechanical parts (e.g. electric/petrol motor, rotating impellers) at the ground surface for easy maintenance. The advent of the electrical submersible pump has partly replaced the need for jet type well pumps, except for driven point wells or surface water intakes.
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