Radial vs. axial: the difference

In motors, bearings, and other moving components, the prefixes “radial” or “axial” are often used. They provide an important indication of the component’s function and direction of movement. The terms are largely the same internationally, which reduces the risk of confusion in cross-border trade and communication. Here you can find out what the difference between radial and axial is:

Radial – everything that “rotates”

A radial movement is always circular. The angle of rotation can be any value. The only important point is that the component does not change in length, but performs only a rotational movement. Radially acting components include, for example, rotary motors, fans, angle radial valves, rotary axes, radial pumps, or, more generally, shafts.

Axial – everything that “moves”

An axial movement always runs along a linear axis. This is where this form of movement gets its name. In hydraulics or pneumatics, axial motors are linear cylinders. When a linear motor is activated, the piston extends or retracts, depending on how the component is pressurized.

Combined components with radial and axial movement

In hydraulics and pneumatics, there are some cases in which a component performs both movements. This includes piston pumps. Both the in-line piston pump and the radial piston pump have both radial and axial acting elements. In both cases, the radial elements are the central rotary axis and the swash plate (in-line/axial piston pump) or the eccentric (radial piston pump). In both cases, the axially acting elements are the pressure pistons. They perform a purely linear movement within their cylinder, regardless of how the rest of the assemblies behave.

A major technical challenge is the manufacture of cylinders that must perform a rotational movement at the same time as extending. As a rule, this only works with the use of guiding elements.

Radial and axial in bearing technology

Confusing radial and axial is particularly dangerous in shaft bearing arrangements. The bearings used, especially multi-part tapered roller, spherical roller, or rolling bearings, must be selected and installed correctly. Otherwise, they not only fail to perform their function, but can quickly damage the entire assembly.

Radial bearings are comparatively wide in design. They absorb forces acting perpendicular to the shaft. This can be the shaft’s own weight. Radial bearings must also reliably absorb and dissipate the resulting reaction forces.

Thrust bearings absorb the linear forces of a shaft—along its axis. They are mostly used on the underside of vertical shafts. They are thinner than radial bearings, but have a narrower cross-section. If they are to be installed along the shaft, the shaft must be designed with suitable shoulders to transfer the axial forces. Combined radial-thrust bearings are also available for special cases.

Selecting components to suit the radial vs. axial difference

Radially or axially acting components are always related to their corresponding reaction forces. They must therefore always be selected so that they can absorb these reaction forces for the required service life.