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5.4: Types of Fixed-Displacement Pumps and Their Applications

Fluids 2: Basic Hydraulics · LibreTexts

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    From LibreTexts, under CC BY 4.0, as the source states it; its equations are written in TeX, which the PDF shows typeset. This page at LibreTexts.

    Hydraulic systems commonly use fixed-displacement pumps to deliver a steady flow of fluid. The three most frequently used types are:

    • Gear pumps
    • Vane pumps
    • Piston pumps

    All of these pumps operate on the positive displacement principle, meaning they move a set volume of fluid with each rotation of the pump shaft. However, their internal mechanisms differ, affecting their performance, efficiency, and application.

    Gear Pumps

    Diagram of a gear pump showing oil flow through drive and idler gears.
    Figure \(\PageIndex{1}\): Diagram of a gear pump.

    A gear pump consists of two meshing gears enclosed within a housing:

    • The drive gear is connected to the pump shaft and receives power from a motor.
    • The idler gear rotates in sync with the drive gear.

    Operation

    1. As the gears rotate away from each other at the inlet side, they create an expanding volume, generating a partial vacuum. This allows atmospheric pressure to push oil from the reservoir into the pump.
    2. The oil becomes trapped between the gear teeth and the housing, then carried to the outlet side.
    3. As the gears mesh together again, they force the oil out into the system.

    Application

    Gear pumps are affordable and commonly used in low- to medium-pressure applications, such as trash compactors and industrial lubrication systems.

    Vane Pumps

    Diagram of a vane pump.
    Figure \(\PageIndex{2}\): Diagram of a vane pump.

    A vane pump consists of a rotor with several sliding vanes housed inside a cam ring.

    Operation

    1. As the rotor spins, centrifugal force pushes the vanes outward against the cam ring.
    2. The off-center rotor position creates an expanding volume at the inlet, generating a partial vacuum that draws oil in.
    3. The oil is trapped between the vanes and housing and is carried around to the outlet.
    4. At the outlet, the decreasing volume forces the oil out into the system.

    Application

    Vane pumps are often used where moderate efficiency is needed, such as in plastic injection molding machines and hydraulic presses.

    Piston Pumps

    Diagram of a piston pump.
    Figure \(\PageIndex{3}\): Diagram of a piston pump.

    A piston pump uses multiple reciprocating pistons arranged inside a rotating barrel. The movement of these pistons is controlled by an angled swashplate.

    Operation

    1. As the barrel rotates, the swashplate angle causes the pistons to move in and out.
    2. On the inlet stroke, pistons retract, creating a vacuum that draws in fluid.
    3. On the outlet stroke, the pistons extend, forcing oil out under pressure.

    Application

    Piston pumps are the most efficient but also the most expensive. They are used in high-pressure applications, such as hydraulic presses, injection molding machines, and heavy machinery.

    This page titled 5.4: Types of Fixed-Displacement Pumps and Their Applications was last modified on Tue, 29 Apr 2025 17:54:29 GMT and is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Jessy Haid.