Pumps and Motors PT2

Velocity Pumps

Uses an impeller or propeller to accelerate water to a high velocity within the pump casing

• low pressure water is converted to high pressure

• Low velocity water as the volume of the pump casing increases

• Volute-type of centrifugal pumps are most common type of pump used by water systems by varying shapes & sizes. They can develop as much as 250ft of head per stage & range in efficiency between 75-85%.

Volute

Centrifugal Pumps

Diffusers Vanes (or changes)

Vertical pumps

Radial Flow

• Water is thrown outward from the center of the impeller and into the volute or diffusers. The velocity is converted to pressure in the volute or diffuser

• Each stage pressure increases but flow capacity is limited to that of the first

• common centrifugal pump installed in water systems

Axial Flow

• Often called the propeller pump and doesn’t have a volute or diffuser vane

• increases head by the lifting action of the blades on the water and water moves parallel to the pump shaft

• can move large volume of water but adds very little head to the water, shaft of propeller pump rotates between 9-15k RPM.

Mixed flow

• Combo of radial & axial flow

• pump type impeller shaped so that the centrifugal force will impart some radial force.

• Used in applications such as raw water pumping and water contains a high solids concentration.

Theoretical suction lift @ sea lvl

34ft

Practical suction lift

15-25ft

Centrifugal pumps Advantages

• Wide capacity ranges

• 1-50k gpm & 5-700ft of head

• Uniform flow @ constant speed & head

• Minimal suspended matter will not jam pump

• low-moderate initial cost

• adaptable to different drive types Motor, Engine, Turbine

• Moderate to high efficiency at optimal operation

• no need for internal lub-low operating noise lvl

• Ability to operate against closed discharge valve

Centrifugal pumps disadvantages

• Narrow range of discharge flows & head for optimal efficiency

• flow capacity is dependent upon discharge pressure (higher pressure = lower flow)

• not self priming

• potential for backward rotation if stopped with open discharge valve ( Can cause pump & motor damage)

• Impeller can be damaged by abrasive material in the water being pumped

closed type of impeller

For pumping water with a low volume of solids.

The resistance of a material to the flow of electrical current

is measured in Ohms.