Frequently Asked Questions

1.800.959.0146

phone

What is a rotary union?
What is a timing valve?
What is a hydrostatic union?
What is a slip ring?
What do you need to know to specify a rotary union for my application?
Do you keep inventory of all of your standard products in stock?
What are the typical delivery times for standard products?
Can standard products be modified to fit my application?
Can I pass multiple media through the same multiple passage rotary union?
What mounting options do you offer?
Do you offer custom rotary unions and what is the process to procure one?
What is a typical delivery for a custom rotary union?
What is the largest custom rotary union that you can manufacture?
Does your standard one year warranty apply for a custom rotary union?
What are my options for material choices for the rotary union?
Are your unions tested prior to shipping?
Can your rotary unions be rebuilt?
What causes rotary unions to fail?

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.
Return to top

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. 
Return to top

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.
Return to top


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.
Return to top


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.  Use our <Inquiry> form to get started.
Return to top


Do you keep inventory of all of your standard products in stock?
We keep inventory for our standard product line and many custom products.  Occasionally, we may be out of stock on an item, in which case, delivery would typically be 4 weeks.
Return to top


What are typical delivery times for standard products?
Delivery on standard, in-stock products is one week from time of order.  In some emergency cases, product can be shipped the same day.
Return to top
 

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.
Return to top


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.
Return to top

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.
Return to top


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.
Return to top

What is a typical delivery 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.
Return to top


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.
Return to top


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.
Return to top


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.
Return to top

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 Type

Typical Applications

Pressure

Speed

Leakage

O-Ring Air, vacuum, water <220 psi air Low None
Energized CF/Teflon Hydraulic, air, water, etc. 7000 psi (<500 psi air) Low to moderate None
Lip High pressure Hydraulic < 10,000 psi Low to moderate None
Mechanical Air, hydraulic, coolant, water <1000 psi (<200 air) Up to 12000 RPM Minimal
Hydrostatic Hydraulic 3000 psi Up to 3000 RPM Controlled

Table 1 - Application Chart
Return to top


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.
Return to top


Can your rotary unions 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 Repair Request Form and send via fax, or email info@rotarysystems.com to initiate the process.
Return to top


What causes rotary unions 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.
Return to top