Pumps

A hydraulic pump operates on positive displacement, where a confined fluid is subjected to pressure using a reciprocating or rotary action. The pump's driving force is supplied by a prime mover, such as an electric motor, internal combustion engine, human labor (Figure 1), or compressed air (Figure 2), which drives the impeller, gear (Figure 3), or vane to create a flow of fluid within the pump's housing.

A hydraulic pump’s mechanical action creates a vacuum at the pump’s inlet, which allows atmospheric pressure to force fluid into the pump. The drawn in fluid creates a vacuum at the inlet chamber, which allows the fluid to then be forced towards the outlet at a high pressure.

The different types of pumps (i.e., gear, vane, and piston) utilize different mechanisms to create fluid flow and pressure.

• Gear pump: Two meshing gears rotate in opposite directions, creating chambers that expand and contract, which generates fluid flow and pressure.
• Vane pump: Vanes are pushed outwards by centrifugal force and pushed back into the rotor as they move past the pump inlet and outlet, generating fluid flow and pressure.
• Piston pump: A piston is moved back and forth within a cylinder, creating chambers of varying size that draw in and compress fluid, generating fluid flow and pressure.

A hydraulic pump's performance is determined by the size and shape of the pump's internal chambers, the speed at which the pump operates, and the power supplied to the pump. Hydraulic pumps use an incompressible fluid, usually petroleum oil or a food-safe alternative, as the working fluid. The fluid must have lubrication properties and be able to operate at high temperatures. The type of fluid used may depend on safety requirements, such as fire resistance or food preparation.