Whenever the design engineer has to cope with the task to convey media into or through rotating machine parts, he utilises the component “rotating union”. Usually, media such as water, hydraulic or thermal oil, compressed air, vacuum, coolants etc. are conveyed by this component into the rotating machine part.

Although the design engineer cannot influence the wear of a rotating union, which results from technical parameters of the application such as speed, pressure, temperature, flow, volume and flow velocities of the media, he can increase the service life by design pre-sets.

You should know that in case of current rotating unions, sealing between the rotating element, “rotor”, and the stationary part, “stator”, is almost always realised by mechanical seals with technical finesses. Due to their bearing, it is important that rotating unions can easily be rotated in mounted condition without any warping. But the industrial bearings are often warped already during assembly because of improper hose lengths or screwing parts. A reduction of the service life is caused thereby.

Can a design engineer assume that the foreman or person who puts the rotating unit into operation knows the importance of correct assembly of a rotating unit?

The latter should (actually) know that
- first the flexible industrial hoses are to be attached to the rotating union and that it is then connected to the shaft end by screwing at the prescribed torque.
- the hose must not show any twisting and be laid without any stresses
- it must not be connected directly to a solid professional pipe
- the vents for controlled leakage point at the right direction,

but: can the above really be assumed? ...