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A jet or eductor pump is a device which uses a stream of one fluid to pump another by application of the Venturi effect. A jet pump achieves its action by using an independent fluid flow to create a Venturi vacuum in the pump mechanism which sucks the fluid through to the discharge hose. Jet pumps exhibit the beneficial characteristic of being able to convert a high energy, low volume flow into a low energy, high volume flow. They are also able to pump fluids containing high levels of abrasive material which would quickly destroy the moving parts of a conventional pump. When used to pump well water, jet pumps also have the advantage of locating all the moving parts of the pump on the surface with only the Venturi section underground.
The Venturi effect used in jet pumps occurs when a fluid is forced through a restriction. This causes a simultaneous increase in the kinetic energy and decrease in the pressure of the fluid flow. This pressure decrease is used in a jet pump to draw fluid into and through the Venturi chamber, thereby completing the pumping cycle. This method of moving fluids has the benefit of turning a relatively high energy flow of fluid at small flow rates into a large flow rate with low energy. This makes the jet pump ideal for applications requiring a high delivery rate with a moderate head.
In some cases, a simple arrangement using a fire hose as an independent fluid source can deliver considerable discharge volumes. In general though, a small centrifugal pump is used to supply the independent fluid flow. Typically a portion of this pumps flow is sent to the jet pump discharge and the rest is used to create the Venturi effect. When used to pump well water, it has the benefit of locating all moving at ground level and only having the Venturi head, Venturi inlet, and discharge pipes submerged in the well. Although submersible electric pumps are gradually replacing the jet pump, they are still used where low maintenance solutions are required.
The jet pump has an additional benefit in that the lack of moving parts in the Venturi makes pumping suspended silt a viable option. This would not be feasible with a conventional centrifugal pump as the sand would quickly abrade the impeller and destroy the pump. The relatively small size of the centrifugal pump in relation to the large discharge rates also makes jet pumps an attractive option from a financial perspective in terms of installation, running costs, and maintenance.