Deepwell Jet Pump

Deep well jet pumps are usually for wells with a pumping lift of 22 to 120 feet (Figure 1). A deep well jet pump combines two principles of pumping that of the centrifugal pump and that of an injector (nozzle and venturi assembly).

Operation
The pump and pipe system are full of water. The water in the pump impeller is thrown outwards by the vanes of the spinning impeller.

As the vanes throw the water out, a vacuum is created at the eye of the impeller, and more water is drawn in to replace that which was thrown out. Some of the water discharged by the impeller passes out of the pump and into the pressure tank. The rest is recirculated through the drive line to the injector in the well. In the injector, the nozzle and the venturi create a vacuum. This vacuum draws water from the well, through
the foot valve. As the water passes through the venturi tube into the suction line, the pressure is increased sufficiently to force the water back to the pump impeller.

The injector nozzle and venturi tube size must be selected according to the pumping depth, the distance the pump is offset from the well and the size of the pump. All pump companies provide charts for proper pump and injector selection. Because of the amount of water being circulated in this type of pumping system, it is important that the proper sizes of suction and drive lines are used to maximize efficiency.

Application
 

• Deep well jet pumps:can be offset from the well
• can be adapted to wells of various depths and yields
• are relatively trouble-free if properly selected, installed and adjusted
• can be primed on long offsets through uneven terrain
• are relatively inexpensive

Limitations
Pumping abrasives, such as sand, will wear the impeller and can wear the mechanical seals causing leaking around the pump shaft.

Deep well jet pumps become less efficient as pumping lift increases. For lifts greater than 80 feet, submersible pumps may be preferred if the well yields sufficient sand-free water. Jet pumps are relatively inefficient at pumping water containing air or gases.

Jet pumps will lose their prime if the water level in the well drops below the foot valve. This result can be prevented in a slow yielding well by using an automatic pressure regulator and a weak well tailpipe below the injector (Figure 3). This tailpipe system will automatically adjust the pumping rate to the well capacity. The mechanical seal on the pump shaft is water lubricated and water cooled, so the pump should never be run without the pump casing being filled with water.