All You Need to Know about the Hydraulic Rotary Unions

A hydraulic rotary union is a device used to transfer fluids and gasses from one point to another point under high pressure. Its function is to stop the input valve to mix with output while rotating.

It is available in many sizes, shapes, and configurations, to meet the requirement of variegated applications. It has four basic parts: a housing unit, a shaft, a bearing, and a seal. These parts are described as follows-

  • Housing unit: It holds other components of the rotary union together. A hose supplying the medium is attached to an inlet port on the housing unit. It is a threaded port. There is a possibility that the rotary union may have an outlet port as well. This happens when the rotary union is being used to supply as well as remove fluid from a roll. If the rotary unions are small, the housing unit is stationary, whereas, if the rotary union is big then the housing unit is attached to the drum.
  • Shaft: It is responsible for carrying the source from the rotary union to the drum.
  • Bearing: This part helps a part of the joint to rotate. The rotary union may consist of one or multiple bearing. The bearing can be a roller or non-roller bearing. Ball bearings and tapered are examples of the roller bearing and graphite bearing and bronze brushing comes under the nonroller bearing.
  • Seal: It is the most important part which stops the source from leaking while operating.


  • Multiple port rotary union: Its shape is like a perforated cylinder. It consists of a threaded screw at the end, which locks on to the output. There are chambers in multiple ports which stop the mixing of material.
  • Straight port rotary union: in this type, the medium is directly transferred through a rotary union

Operating parameters:

  • Speed: normal rotational speed varies from 0 to 1000 RPM and applications having high-speed need 10,000+ RPM.
  • Pressure: its normal pressure varies from 0 to 20,000 PSI and some applications require a pressure of 40,000+ PSI.
  • Temperature: its temperature varies from -150 degree F to +400 degrees F.


It is used in the following industries:

  • Agriculture
  • Car washes
  • Textiles

Following are the important parameters considered to select the right rotary joint

  • Speed of machine
  • Fluid to transfer (coolant, cutting oil, etc.)
  • Pressure and temperature
  • Degree of filtration needed for the fluid
  • Type of connection to the machine.

The entities engaged in manufacturing the hydraulic rotary unions should make use of the finest grade materials and modern techniques in order to engineer a quality grade product. By adopting the fair market practices and competitive pricing policies, the suppliers of these tools can surely attain a remarkable position in the market.