Creating Suction

Shallow well pumps are positioned above the well and force the water up from the well using suction. The keys to creating the suction are the impeller and the volute tube. The pump is powered by a motor that drives an impeller. The impeller spins, forcing water through it and creating a vacuum. The negative pressure in the volute pulls the water to the pump.

Prime the Pump

Since shallow well pumps use water in order to draw water, they typically need to be primed. The water fills the impeller housing so that the entire impeller is submerged and all air is evacuated from the system. A check valve is used to keep the water in the pump and plumbing system from flowing back down into the well.

Centrifugal Pumps

A centrifugal pump is normally a low-pressure, high-volume pump. A centrifugal pump is going to create a vacuum from the impeller in the suction pipe in order to lift the water. Centrifugal pumps do not create enough pressure to be useful for home wells. Instead, they are used for irrigation systems or to fill holding tanks in order to water livestock.

Jet Pumps

Some, but not all, jet pumps create pressure in the volute, which forces water through a venturi, creating a vacuum in the suction line. In turn, this creates high pressure with low volume. Jet pumps pull sufficient water for household use.

Depth of the Well

The end of the suction pipe with the foot valve should not be deeper than 25 feet in a well. At greater depths a shallow well pump cannot create enough vacuum to lift the weight of the water.

Source:

How It Works: Water Well Pump

Inspectapedia: Single Line Jet Pumps & Water Wells, Explanation & Repairs