How a Pump Works

 

All pumps use basic forces of nature to move a liquid. As the moving pump part (impeller, vane, piston diaphragm,etc.) begins to move, air is pushed out of the way. The movement of air creates a partial vacuum (low pressure) which can be filled up by more air, or in the case of water pumps, water. This is similar to sucking on a straw. A partial vacuum is created in your mouth when you suck on the straw. The liquid is pushed up the straw because of the pressure differences between your mouth and the atmosphere.

The pumping action is your mouth closing around the liquid (in your mouth) and forcing it down your throat.

ATMOSPHERIC PRESSURE
At sea level, mother nature exerts a pressure of 14.7 psi all around us. If one end of a tube is placed in water and a perfect vacuum is applied to the other end, that 14.7 psi could hold a column of water 33.9 feet high. This is only obtainable at sea level and with a perfect vacuum.
In reality, ALL centrifugal pumps can lift water no more than 26 feet at sea level. This drops off approximately 2 feet for each 1000 feet of altitude above sea level.

PRESSURE DIFFERENCES (suction)

In nature, movement is from more dense to less dense. Weather systems are tracked as high pressures move toward low pressures. In batteries, one end contains more positively charged particles that move to the end with the negatively charged particles.

A liquid under high pressure will move to an area of less pressure if a path is provided.

CENTRIFUGAL FORCE
The centrifugal pump works in the same way as sucking on the straw. As the engine starts, the impeller turns which forces the water around it out of the pump's discharge port. The partial vacuum created, allows the earth's air pressure to force water up the suction hose (straw), and into the suction (inlet) side of the pump to replace the displaced water. When the water hits the rotating impeller, energy of the impeller is transferred to the water, forcing the water out (centrifugal force). The water is displaced outward, and more water can now enter the suction side of the pump to replace the displaced water.

SEALED SYSTEMIf a water pump is to create a partial vacuum in the pump housing, three things must happen:
The pump must be primed. The water in the housing is essential to lubricate the mechanical seal so that it won't wear and leak.

The suction hose, hose seals and all O-rings must be in good condition so air can't be drawn in, losing the vacuum.

The impeller-to-volute clearance must be within specification to achieve the proper vacuum.