Rotary unions and hybrid joints
BGB Rotary unions and hybrid joint
Hydraulic rotary unions with a four-port flagship design (ports can be blocked off) and custom builds, often combined with BGB slip rings or FORJs in a single package.
Key specifications
| Passages | 4 ports standard (2 commonly used); custom designs available |
|---|---|
| Media | hydraulic fluid |
Summarised in our own words from BGB (family-owned; legal entity name not stated on its website)'s published data; series maxima, individual models vary. Last checked 2026-10-30. Source 1
Notes on this data
No pressure, speed or size figures published on the page read.
Specify Motion is not affiliated with BGB (family-owned; legal entity name not stated on its website). BGB and Rotary unions are used only to identify the product. Comparisons use published figures; always confirm against the current datasheet.
Typical applications
Alternatives that meet or exceed these figures
Engineers often come to us with a BGB part number and leave with an alternative that is easier to source, quicker to deliver or a better fit for the machine. These 2 series from our supply network are the closest match on published figures.
A rotary union that passes air, gases or fluids through rotating interfaces, optionally combined with electrical circuits in one unit. Size, ports and channel count are customised to the machine.
View series →Combined units passing hundreds of electrical circuits plus up to 16 gas or liquid channels, with pressures of 10 MPa or more.
View series →Figures are the highest published for each series and are not always measured the same way. A higher figure is not automatically a better choice: mounting, duty cycle, feedback, connectors and approvals matter too. An engineer will check the fit against your application before recommending anything.
What a rotary unions and hybrid joint is
A rotary union, also called a rotary joint or swivel, transfers fluids such as compressed air, vacuum, hydraulic oil, water or coolant from a fixed supply into a rotating shaft or table. A rotating shaft runs inside a stationary housing, and each fluid passage is isolated by seals between grooves, so several media can pass through one unit. Many designs combine with an electrical slip ring into one assembly, providing both fluid and electrical paths through continuous rotation.
When engineers choose a rotary unions and hybrid joint
Choose a rotary union when pneumatic grippers, vacuum cups, hydraulic clamps or cooling circuits sit on a rotating part. The alternative of hoses limits rotation to a few turns. The trade-offs are seal friction, leakage and wear: seal choice sets pressure, speed and media compatibility, and dry running damages some seals. Mixing vacuum and pressure in one unit needs suitable seals. Combining the union with a slip ring saves space but makes the assembly larger and more application-specific.
How to specify the BGB Rotary unions
Send these with your enquiry and an engineer can confirm the right Rotary unions variant or an equivalent:
- Number of passages and the medium in each
- Pressure and vacuum levels (bar)
- Flow rate or port size (l/min, mm or BSP)
- Fluid temperature (°C) and compatibility
- Speed (rpm)
- Permitted leakage and drain or vent provision
- Electrical circuits if combined with a slip ring
Common mistakes to avoid
- Running a union designed for lubricated media on dry air or without flow
- Not providing a leak drain between media and the electrical section of a combined unit
- Applying side load from rigid pipework instead of using flexible hoses and a torque arm
- Ignoring pressure spikes from valve switching when choosing seals
BGB Rotary unions: frequently asked questions
What is the BGB Rotary unions?
Hydraulic rotary unions with a four-port flagship design (ports can be blocked off) and custom builds, often combined with BGB slip rings or FORJs in a single package. It is made by BGB (family-owned; legal entity name not stated on its website); Specify Motion can help source it or propose an equivalent.
Who makes the BGB Rotary unions?
The BGB Rotary unions is made by BGB (BGB (family-owned; legal entity name not stated on its website)) and is listed here for engineers comparing options. Specify Motion is not affiliated with BGB (family-owned; legal entity name not stated on its website); brand names are used only to identify the product.
Is there an alternative to the BGB Rotary unions?
Yes. On published figures, QR Series Pneumatic/Hydraulic Rotary Joint and Pneumatic/Hydraulic Integrated Electrical Slip Ring are the closest match from our supply network. An engineer confirms the fit against your application before recommending anything.
Can one rotary union pass air, vacuum and water at the same time?
Yes, multi-passage rotary unions isolate each medium in its own groove with seals between them. Each passage must be specified with its medium, pressure and flow, because seals that suit air may not suit water or vacuum. Leakage paths between passages and a drain for any seepage should be agreed with the supplier.
How is a rotary union combined with a slip ring?
A common layout puts the rotary union on the axis and the electrical slip ring around or beside it in a single assembly, so both fluids and electrical circuits pass through one rotating connection. The design must keep fluid away from the electrical rings, often with a drain chamber. Specify both parts together so the supplier can manage sealing, length and bearing loads.
Further reading: How to select a rotary union · How to select a slip ring · Slip rings
Other rotary unions and hybrid joints series
Spec builder
Specify what you need instead of Rotary unions
Select every part you need, answer the questions an applications engineer would ask, and see your summary before we ask for any details.
- 1Products
- 2Performance
- 3Environment
- 4Volumes
- 5Your spec
Engineer support
Let our experienced engineers do the hard work for you
Tell us how you use the BGB Rotary unions: the load, speed, duty and environment. Our engineers will confirm whether it is still the right part, find it for you, or propose an alternative that fits better.
- Reviewed by an engineer, not an autoresponder
- Like-for-like and better-fit alternatives
- Standard, modified and custom options
Prefer to configure it? Use the spec builder.