Frequently Asked Questions

General Questions

Rotary Union Questions

  • What is a rotary union?

    A rotary union is used to continuously transmit from a stationary source to a rotating destination, or vice versa. They are available in a wide variety of configurations, connection types and materials to fit most applications.

    See Extended Rotary Union Definition ›

  • What is a hydrostatic union?

    Hydrostatic unions incorporate a close-tolerance “gap” seal, which has a ground shaft OD mated to a precision-honed housing bore with drain to reservoir. Available in single or multi-passage configurations, these unions are appropriate for high pressure and higher speeds (> 1000 RPM) applications such as machine tool chucks—but are also found in low speed applications such as wind turbine pitch control systems. The contact-free nature of this union means cool running, low torque, and very long life.

  • What is a timing valve?

    Similar to rotary unions, timing valves transmit pressure and flow from a stationary source and a rotating destination, but are designed to so at a predetermined angle of orientation. This allows flow to be controlled to fixtures on an index table for clamping and unclamping. Contact your Applications Engineer for more information.

  • What do you need to know to specify a rotary union for my application?

    The “Big Four” are Media, Pressure, Temperature and RPM. Other parameters such as number of passages, connection sizes and flow requirements will aid us in specifying the appropriate union. Contact us to get started.

  • What are my options for material choices for the rotary union?

    Some options are (but not limited to): carbon steel(s), stainless steel, SAF 2507 super duplex stainless steel, aluminum, brass, cast forgings, hastelloy, a wide variety of plastics and other exotic materials.

  • Can I pass multiple media through the same multiple passage rotary union?

    Generally speaking, you can pass multiple media through the same rotary union without cross contamination. Please consult with one of our Applications Engineers to discuss your application in detail to ensure proper seal compatibility for all media.

  • What are my options for seals in a rotary union?

    Some options are (but not limited to): O-rings, Proprietary Teflon seals, Lip seals, Mechanical Face Seals and Hydrostatic with controlled leakage.

    Seal TypeTypical ApplicationsPressureSpeedLeakage
    O-RingAir, vacuum, water<220 psi airLowNone
    Energized CF/TeflonHydraulic, air, water, etc.7000 psi (<500 psi air)Low to moderateNone
    LipHigh pressure Hydraulic<10,000 psiLow to moderateNone
    MechanicalAir, hydraulic, coolant, water<10,000 psi (<200 air)Up to 12000 RPMMinimal
    HydrostaticHydraulic3000 psiUp to 3000 RPMControlled
  • What mounting options do you offer?

    There are several ways to mount rotary unions. With our standard product line we offer a flange mount and NPT mount. With the flange mount, you seal off statically on the end of our shaft with O-rings that are provided. With the NPT mount, you thread your fittings directly into the NPT ports that are provided. There are also many other options available with a custom rotary union.

  • Can standard products be modified to fit my application?

    In most cases, our standard products can be modified to fit into your application. Modifications may include adding drilled and tapped holes, relocation of ports, and bearing protection, to name a few.

  • Do you offer custom rotary unions, and what is the process to procure one?

    We are the industry leader in custom designed rotary unions. One of our Applications Engineers will work directly with you on your custom requirement. Once we have an idea of your design, we will provide you a detailed quote with delivery. After receiving a Purchase Order, we will provide you with a detailed print to review and sign off prior to manufacturing.

  • What is the largest custom rotary union that you can manufacture?

    The largest rotary union that we have manufactured to date is over 40.0” in diameter. This rotary union is used for a medical image scanning application. We have the in-house capacity to manufacture rotary unions up to 60.0” in diameter, in production volumes.

  • Does your standard one-year warranty apply for a custom rotary union?

    Yes, in most cases we will offer our standard one-year warranty. On very rare occasions we will not be able to offer a warranty, but this will be disclosed up front during the initial discussion and quotation process.

  • What are typical delivery times for a custom rotary union

    Delivery times will vary depending on complexity of the custom rotary union. Typical delivery is 8 weeks for general materials, and longer for special materials and plating.

  • Are your unions tested prior to shipping?

    Our unions are run-in and 100% tested under pressure to ensure they are ready for immediate installation upon arrival.

  • What causes a rotary union to fail?

    When installed properly, your Rotary Systems rotary union will provide years of trouble-free service. However, common causes of early failure are hard piping, side loading, heat generated from excessive speed, and unfiltered media. See our Installation Instructions for detailed information.

  • Can a rotary union be rebuilt?

    Yes. The vast majority of our unions can be rebuilt. We offer two options:

    1. Depot Repair – We will evaluate your union free-of-charge (in most cases) and provide an estimate for repair. Our rebuilt unions carry our full one-year parts and workmanship warranty.
    2. Field Rebuild – Both short kits (o-rings and/or seals) and long kits (includes bearings) are available for our unions for on-site rebuild.

    Please fill out our Return Authorization Form to initiate the process.

Slip Ring Questions

  • What is a slip ring?

    Slip rings do the same for electrical power and signal that rotary unions do for fluid media. They are often integrated into rotary unions to send power and data to and from rotating machinery. Common uses are for power, proximity switches, strain gages, video and Ethernet signal transmission. See Rotary Systems line of slip rings here.

    See Extended Slip Ring Definition ›

  • What do you need to know to specify a slip ring for my application?

    Assembly Type

    The first thing that needs to be defined is the type of assembly required of which there are two basic types:

    1. Separate slip ring & brush block assemblies (no bearings or mounting hardware).
    2. Self-contained slip ring assemblies with their own bearing arrangement.
      • Fully enclosed capsule slip rings.
      • Packaged slip rings with accessible terminals.

    Ring Configuration

    The ring configuration needs to be considered based upon the space available within your system:

    1. Drum type where each ring is adjacent to the next along the central axis.
    2. Pancake type where each ring is concentric to the next (this looks a bit like a record).

    The drum type is the more common, the pancake type being specified when axial length is limited. The available space within the system will define the mechanical envelope and by giving up the maximum space available in the system to the slip ring you will increase the chances of utilizing an existing design.

    System Interface Requirements

    1. Is a through bore required for shaft mounting or for the routing of hydraulics or pneumatics?
    2. How will the slip ring assembly be mounted in the system? Hard mounting of both the rotor and the stator should be avoided as this can overload and damage the slip ring bearings if there is any misalignment within the system.
    3. What sort of electrical connections does the slip ring assembly need? Connectors, terminals, leads or a combination of the three? If leads are required what is length needed and should they exit in an axial or radial direction?

    Electrical Requirements

    The electrical requirements should also be defined, and by specifying the current we can propose an assembly with the correct ring cross-section, brushes and termination. The voltage required will determine the spacing between adjacent rings and brushes. The current and voltage of each ring or group of rings should be specified individually as this will enable us to provide the most economical solution within the smallest space envelope possible.

    Operating Speed

    The operating speed is a critical consideration in defining the mechanical requirements. The speed, diameter and the required operating life of the application will dictate which contact materials are suitable. Will the assembly rotate at a continuous speed or will it oscillate?

  • Can standard products be modified to fit my application?

    In most cases, our standard products can be modified to fit into your application. Modifications may include adding connectors, terminal boards, wire harnesses, as well as internal modifications and custom enclosures, to name a few.

  • Do you offer custom slip rings, and what is the process to procure one?

    Rotary Systems specializes in custom designs for your application. One of our Applications Engineers will work directly with you on your custom requirement. Once we have an idea of your design, we will provide you a detailed quote with delivery. After receiving a Purchase Order, we will provide you with a detailed print to review and sign off prior to manufacturing.

  • What is the largest custom slip ring that you can manufacture?

    The largest slip ring that we have manufactured to date is over 48.0” in diameter. This slip ring is used for a wind turbine application.  We have the in-house capacity to manufacture slip rings up to 60.0” in diameter, in production volumes.

  • Does your standard one-year warranty apply for a custom slip ring?

    Yes, in most cases we will offer our standard one-year warranty. On very rare occasions we will not be able to offer a warranty, but this will be disclosed up front during the initial discussion and quotation process.

  • What are typical delivery times for a custom slip ring?

    Delivery times will vary depending on complexity of the custom slip ring. Typical delivery is 8 weeks for general materials, and longer for special materials and plating.

  • Are your slip rings tested prior to shipping?

    Our slip rings are run-in and 100% tested to ensure they are ready for immediate installation upon arrival.