What is a rotary joint?
A rotary union (frequently referred to as rotary joint) is a mechanical device between a fixed part, often a flexible hose, and a rotating part of the machine. This can be for example a shaft of a cylinder or index table of a machine. The union can pass a fluid from the fixed part to the rotating part of the machine. Common fluids are air, steam, water, thermal oil, or hydraulic oil. Rotary unions are available in different configurations: single passage where the flow is only in 1 direction, but also dual flow where the fluid will enter and return through the same union, and multi pages passage union where multiple channels are available the same or different fluids that needs to be transferred.
How to select a rotary union?
6 variables are important selecting a rotary union: pressure, speed (RPM), temperature, fluid, volume, and number of passages
Pressure: the pressure of the fluid influences the seal and/or bearings of the rotary union. Higher pressure will limit the number of unions that can be used.
Speed: The rotational speed influences the bearings and seal. The seals are closing the fluid between the rotating part of the machine and the stationary part. They are subject to friction and are wearing parts.
Temperature: the temperature affects many parts in the rotary union: seals, bearings, and choice of materials. Mechanicals seal often arrive at 340°C (640°C). O-ring or lip seals the temperature is determined by the limits of the material of which they are made. The temperature is influenced by the fluid temperature and the additional friction in the mechanical seal and bearings.
Fluid: the fluid influences the seal. Some seal materials are good for water while others are good for oil or air. Some fluid enters between the rotating and stationary parts. Depending on the choice the fluid will lubricate the seal and improve the performance, in other applications the seal will perform worse with the fluid between the 2 parts.
Volume: the determines the size of the passages and thus the size of the union to be used. Important is to consider the speed of the fluid inside the passage.
Number of passages: this determines the configuration of the union. Often rotary unions have 1 or 2 passages and have wide range of seal materials available. When 3 or more passages are required often O-ring or lip seals are a common choice.
Is it possible to repair Johnson-Fluiten rotary joints?
Johnson-Fluiten Service Dept. responds to requests for repair and maintenance of rotary joints, analyzing and replacing wearing parts.
In this way we are able to provide a guaranteed product as new at lower cost. Our dedicated staff is prepared to analyze the reasons of failure and to study better solutions or alternatives.
Is it possible to replace internal seal package of Johnson-Fluiten rotary joint?
The complete R line is featured with a Quick Replacement Design (QRD) which allow you to repair the union while it is still installed on the machine. It is enough to remove the blocking screws and separate the body to replace sealrings and orings.
It is as well possible to quickly adapt the joint to fluids requiring different sealing materials.
The repairkit includes stationary ring, rotating ring, O-ring gaskets and a set of springs.
What is the delivery time for Johnson-Fluiten standard rotary unions?
Our fast shipping service allows us to prepare an order in less than 24 hours after the receipt and to ship it to any destination. An advantage that merges the quality of our products with the accuracy and a specific attention for the customers that choose Johnson-Fluiten.
For any further information about our fast shipping service, please contact us by e-mail:
We will answer you… quickly as well!