Hydraulic Pump Technology & Selection

Pumps are key components of a hydraulic system, generating hydrostatic energy by conveying oil (or another suitable fluid) through machinery in a precisely modulated manner. As hydraulic machinery varies in size, complexity, and functionality, the pumps within these systems vary as well to accommodate the particular demands of the application.

It’s no secret that hydraulic pumps can be found in a broad range of designs, but not everyone understands the distinctions between the different types. These distinctions are more than merely formal in nature, however, and it is important to be aware of the full spectrum of options available to you.

Selecting the wrong pump can lead to a host of adverse consequences: excessive repair and maintenance expenses, costly installation of unneeded components, lost productivity due to downtime, and even potential safety hazards. Having said that, let us examine the various types of pumps available today.

Gear pumps

The gear pump is one of the most frequently encountered types of hydraulic pumps, and for that reason alone it is worth becoming acquainted with it. Its basic design is fairly simple. This pump generates hydraulic energy via the coordinated movement of at least two intermeshed gears.

In general, the device includes a drive gear (itself connected to a drive shaft) whose teeth are interlocked with those of a second gear. The turning of the drive shaft rotates the drive gear, which causes the other gear to rotate in the opposite direction—the pump can be adjusted to turn in either direction, depending on the needs of the application. Through this action it generates a cavity that draws the hydraulic fluid in to the inlet side , Gear pumps do not have good suction characteristics and for best performance the inlets should be flooded and below the level of fluid in the supplying reservoir.

These devices belong to the fixed (positive) displacement family of pumps, and they’re available in two types:

External gear pump – In this design, the two gears are arranged side by side, so that their teeth mesh in the middle of the pump. The fluid is transported through the gap that separates the housing and the outer edges of the gears. These pumps are valued for their ability to function quietly, manage corrosive media, and tolerate pressures up to 250 – 280 bar (which can be assisted by using a cast iron gear housing). Additionally, their reasonably simple construction imposes few maintenance demands.

Internal gear pump – This type of pump features a gear positioned inside a larger gear. As with the external gear pump, the movement of one gear sets into motion the other gear, whose teeth intermesh with it. As the two gears rotate, gaps of varying sizes and dimensions are created, which, in turn, forces the hydraulic fluid out of the outlet port due to the reducing displacement principle. Incidentally, the gerotor pump, which has rotors instead of gears with teeth, can be classified as a type of internal gear pump.

Screw pumps and gear ring pumps are other, less commonly seen varieties of gear pumps for hydraulic applications but operate on more or less the same principles. 

Benefits

Gear pumps are lightweight, fairly inexpensive, and boast a reasonably simple design. As these pumps are not dependent on centrifugal force, they can run efficiently down to around 500rpm if necessary (e.g., to reduce noise levels). Nonetheless, they tend to wear out sooner than other types of pumps as they are very sensitive to contamination of the fluid being pumped.. When mechanical difficulties develop, it’s often more economical to replace a gear pump than to attempt repairs.

Why choose a gear pump for your particular application? They can transport many types of hydraulic media. They are also relatively inexpensive, extremely good power to size ratio, come in many displacement sizes, have a large range of drive options and are widely available. They are often used in cars, trucks, and other types of motorized vehicles, in addition to Industrial applications.

Piston pumps

These types of pumps generate hydraulic energy by harnessing the power produced by one or more pistons. A piston is fundamentally a mobile cylindrical element inside a larger cylinder or casing. When in operation, the piston moves in an up-and-down manner that firstly generates a vacuum, pulling the hydraulic fluid through the inlet of the pump before reversing in direction pushing the fluid out of the outlet port, Common piston pump elements include a drive shaft, swash plate, and compensator.

Piston pumps can be divided into a number of subtypes—a fact that contributes heavily to their usefulness across various industries. These pumps are manufactured in fixed displacement and variable displacement models. A fixed displacement type will transport a specific, unvarying volume of media with each piston cycle. A variable displacement pump can be modified to process different volumes, depending on the particular needs of the application.

Fixed displacement and variable displacement pumps can each be subdivided into axial and radial designs. The axial pump features a number of pistons positioned in a circle inside the cylinder block. The pistons rotate around a central shaft. The radial pump has a collection of pistons arranged in a “star” pattern around an eccentric shaft. As the shaft rotates, the pistons are successively set into motion.

Benefits

Piston pumps can provide a number of advantages. They are capable of tolerating high speeds and high pressure. In fact, they’re capable of tolerating substantially higher pressure than gear and vane pumps. Small in size, they’re easy to move around as needed and, for that reason, can be used effectively in a broad range of settings. Although these pumps can be fairly expensive, their high efficiency compensates for this to a large extent.

Where can you find piston pumps? They’re commonly used in mobile machinery for hydrostatic drives or where very high pressures, >250 bar or efficient variation of flows and or efficient use of available power is required. As these pumps can project an even, pulse-less stream of media they are relatively quiet.

Vane pumps

The basic design of the vane pump features sliding vanes (thin barriers) that are attached like flower petals to a slotted rotor in the center. The vanes extend from this central rotor all the way to the housing, in a way that creates distinct compartments that can each hold hydraulic media. When the rotor turns, the individual compartments bordered by the vanes are carried from the input around to the output, and then back to the input—this process transports hydraulic fluid through the pump in a steady fashion.

In many vane pump designs, the central rotor runs within a cam ring which causes the vane compartments to change in dimension as the rotor is turned. The vanes increase and decrease in length (by means of spring or centripetal force) so that they remain in constant contact with the outer housing / cam ring, thereby preventing fluid leakage. The majority of vane pumps belong to the fixed displacement family. Variable displacement vane pumps are available and normally work by adjusting the shape of the cam ring.

Benefits

Vane pumps produce little noise and minimal vibrations, all while maintaining a reasonably high speed—this makes them an appealing choice for settings where hydraulic systems must operate as unobtrusively as possible. They can also generate a continuous, nearly pulse-free stream of media.

Compared with gear and piston pumps, they’re substantially easier to repair and maintain, which contributes to their quite long working lifespan. That characteristic largely offsets their relatively high upfront costs. Because the vanes remain in contact with the housing due to tension produced by the springs or internal forces the pumps can easily tolerate minor wear to these components without loss of efficiency.

These pumps are commonly found in aviation heavy construction machinery and machine tools..

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