Typical Jet Pump Installations
Jet Pumps are mounted above ground and lift the water out of the ground through a suction pipe. Jets are popular in areas with high water tables and warmer climates.
There are two categories of jet pumps and pump selection varies depending on water level.
- Shallow well installations go down to a water depth of about 25 feet (7.62 m).
- Deep wells are down 150 feet (45.72 m) to water, where surface pumps are involved.
The jet pump is a centrifugal pump with one or more impeller and diffuser with the addition of a jet ejector.
The nozzle receives water at high pressure. As the water passes through the jet, water speed (velocity) is greatly increased, but the pressure drops. This action is the same as the squirting action you get with a garden hose as when you start to close the nozzle.
The greatly increased water speed plus the low pressure around the nozzle tip, is what causes suction to develop around the jet nozzle. Water around a jet nozzle is drawn into the water stream and carried along with it.
For a jet nozzle to be effective it must be combined with a venturi. The venturi changes the high-speed jet stream back to a high-pressure for delivery to the centrifugal pump. The jet and venturi are simple in appearance but they have to be well engineered and carefully matched to be efficient for various pumping conditions. The jet nozzle and venturi are also known as ejectors/ejector kits.
On a shallow-well jet pump the ejector kit (jet nozzle and venturi) is located in the pump housing in front of the impeller. A portion of the suction water is recirculated through the ejector with the rest going to the pressure tank. With the ejector located on the suction side of the pump, the suction is increased considerably.
This enables a centrifugal pump to increase its effective suction lift from about 20 feet to as much as 28 feet.
But, the amount of water delivered to the storage tank becomes less as the distance from the pump to the water increases… more water has to be recirculated to operate the ejector.
The difference between a deep-well jet pump and a shallow-well jet pump is the location of the ejector.
The deep-well ejector is located in the well below the water level. The deep-well ejector works in the same way as the shallow-well ejector. Water is supplied to it under pressure from the pump. The ejector then returns the water plus an additional supply from the well, to a level where the centrifugal pump can lift it the rest of the way by suction.
This is of particular value when you have a water level that is gradually lowering. This will probably require a change of venturi to work efficiently. Because jet pumps are centrifugal pumps, the air handling characteristics are such that the pump should be started with the pump and piping connections to the water supply completely filled with water.
With a shallow-well jet pump, the ejector is mounted close to the pump impeller. With a deep well jet pump, the ejector is usually mounted just above the water level in the well, or else submerged below water level.
Centrifugal pumps, both the shallow-well and deep well types have little or no ability to pump air. When starting, the pump and suction line needs to have all of the air removed. An air leak in the suction line will cause the pump to quit pumping … or sometimes referred to as “losing its prime”.
How a jet provides pumping action?
Water is supplied to the Jet ejector under pressure. Water surrounding the jet stream is lifted and carried up the pipe as a result of the jet action.
When a jet is used with a centrifugal pump a portion of the water delivered by the pump is returned to the jet ejector to operate it. The jet lifts water from the well to a level where the centrifugal pump can finish lifting It by suction.
Jet Pump – Principles Of Operation (VIDEO)
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Reference: Pump Basics: How Centrifugal Pump Works – A.Y. McDONALD MFG. CO.