Introduction To Liquid Movers — PUMPS Hydraulic pumps convert mechanical energy from a prime mover (engine or electric motor) into pressure energy. The pressure energy is used then to operate an actuator. When a hydraulic pump operates, it performs two functions: First, its mechanical action creates a vacuum at the pump inlet which allows atmospheric pressure to force liquid from the reservoir into the inlet line to the pump. Second, its mechanical action delivers this liquid to the pump outlet and forces it into the hydraulic system.
All pumps create flow. They operate on the displacement principle. Fluid is taken in and displaced to another point.
Pumps that discharge liquid in a continuous flow are Rotodynamic.
Pumps that discharge volumes of liquid separated by periods of no discharge are positive-displacement type ” hydrostatic”.
The volume of liquid delivered for each cycle depends on the resistance offered to flow. Kinetic energy is added to the fluid by increasing the flow velocity.
Centrifugal and Axial pumps are examples of non-positive-displacement pumps.
A positive-displacement pump is one that a fixed volume of fluid is displaced (delivered) during each pumping. Constant delivery during each cycle is possible because of the close-tolerance fit between the pumping element and the pump case.
Types of Positive-Displacement Pumps:
Some of them are primarily used for:
moving highly viscous liquids, where it would be difficult to generate kinetic energy in the first place. Some are used for developing high pressure, which would require extensive staging in a kinetically driven device. Some are used to achieve high accuracy of liquid delivery rate .
Gear pumps are primarily used for high-viscosity liquids. Two or more gears trap liquid in the space between the gear teeth and the casing wall and convey it from inlet to outlet. Obviously, it is essential to minimize paths through which liquid could flow backward.
An axial piston pump is a positive displacement pump. the reciprocating piston is driven back and forth by a rotating mechanism.