What Kind of Seals are in a Hydraulic Swivel? And What Do They Do?

December 6, 2016

In order to construct a properly functioning hydraulic swivel, many types of seals must be used. Each seal performs a specified function to ensure the hydraulic swivel operates correctly. At UEA, our seal kit consists of: o-rings, thrust washers, excluder seals, u-cup seals, wear rings, energizers and cap seals.

The o-rings keep the large particulate from getting into the swivel.  The excluder seals are located at the ends and are internal to the swivel and keep the smaller pieces of particulate out. Inside of the excluder is the u-cup which prevents the hydraulic fluid from escaping from the swivel.

Next, the wear rings act as the bearing material and maintain the e-gap between the spool and housing during its operation. The energizer and cap seal are located between each circuit and contain the hydraulic oil within each circuit. We like the circuits at each end of the swivel to be low pressure, with one being a return back to the tank. When a high pressure circuit is needed, a weep circuit is added adjacent to it and is connected to the back of the tank circuit.

The position of the torque arm is located within close proximity to the mounting flange in order to provide smooth rotation during its operation.

If you are interested in learning more about hydraulic swivel seals, check out our blog, How Long do Hydraulic Swivels Last?

Thomas Van Veldhuizen

How Do I Know My Hydraulic Swivel Will Perform?

November 29, 2016

Once a hydraulic swivel has been designed, reviewed and machined, the housing and spool are moved to the clean room and all parts are pulled to make a complete assembly. Then the housing and spool are moved to the assembly machine. Here the spool is pushed into the housing using an air over oil system. The operator manually turns a crank which extends the cylinder rod and slowly advances the spool into the housing, while monitoring the pressure from a gauge until the spool is fully inserted. Doing this operation manually allows the operator to physically feel if there is any binding occurring, which may cause internal damage to the seals, housing and/or spool. The rest of the assembly is completed and the swivel is then placed into our production machine for torque and pressure tests.

Each swivel is prefilled with hydraulic fluid and rotated in both directions while the torque is monitored by load cells. Then the pressure of each circuit is tested at 1.5x the operating pressure, up to a maximum 7500 psi. The pressure is monitored by two pressure transducers, one for even and one for odd circuits. The cleanliness of the oil is continually monitored by an ICM at the 17/15/12 level, thus ensuring we keep the internal circuits of each swivel at a high cleanliness level. The torque, pressure and oil cleanliness are all stored and saved as a birth certificate for each swivel. The fluid in the swivel is then reclaimed back to our oil reservoir. Next, the swivel is removed and all ports are plugged and prepared for primer or primer and paint. Each one is individually banded to a crate, ready for shipping to each client.

Every step in the process provides the client with confidence that each swivel has been put together with the utmost care and will perform to expectations.

For more information on hydraulic swivel production testing, visit our blog.

Thomas Van Veldhuizen

Wind Slip Ring with Terminal Blocks

November 22, 2016

This new electrical slip ring has progressed beyond the design phase and is about to make its way into production at United Equipment Accessories.  The S15D series slip ring assembly with terminal blocks was designed to be installed horizontally in a wind turbine application.  The terminal blocks allow for a custom configuration using modular terminal blocks sized for the amperage and voltage requirements.  In this application, terminal blocks are being supplied for both the stator and rotor side of the slip ring.  This particular application requires 5 circuits for power and 23 circuits for control and communication.Figure 1_terminal blocks

Figure 2_terminal blocksThe S15D series slip ring is in our 1.50” bore slip ring group and is made up of an anodized aluminum dished base casting, anodized aluminum top plate, a molded clam shell style cover for the stator and an anodized aluminum clam shell style cover for the rotor.  A vent plug and thermostat controlled heater were added to eliminate condensation inside the enclosure.  A custom torque arm is supplied to retain the outer part of the slip ring.

The large mounting flange is bolted to the gearbox of the wind turbine after first connecting the typically longer center rotational harness to the terminal blocks inside the rotor hub.figure 3_terminal blocks

Looking for more information on slip rings? You may enjoy reading How Long Does it Take to Manufacture a Slip Ring?

Josh Bockholt
Sr. Designer – Engineering

How long do Hydraulic Swivels Last?

November 15, 2016

Any discussion of hydraulic swivel life would be insufficient without mention of seals. Many different aspects of the application have an effect on the seal life, sometimes the effects will be positive and others will be negative.  Here is a list of items that are important to consider when thinking about the seal life, and then some details on each.  UEA’s seal supplier has witnessed these situations over the years and believes a lot of the failures are a result of one, or a combination, of these.

Hardware Finish

This is kind of a double edged sword, a finish too rough is likely to abrade the seal, thus reducing its life.  However, if the finish is too smooth, the seal may not be lubricated adequately and build internal heat, thus leading to a reduced life.  Basically you want a surface with a good trade off in which you have enough valleys to hold oil.  At the same time you don’t want the peaks of the surface profile to be sharp and rough, as this will abrade the seal.  The specifications (surface finish) provided by our seal provider is based on in-housing endurance testing, as well as field experience.  Every swivel shipped from UEA has documented surface finishes meeting our seal supplier’s specs.


As the pressure in the system increases, the loading in the seal increases as well; thus typically higher pressure applications tend to wear faster than that of lower pressure applications.  On cap seals, in particular, the direction of pressure may have an effect, seals with the same pressure cycle on both sides wear very little.  On the other hand, a seal that only sees pressure from one side will typically wear much faster than the seal with pressure from both sides.  The pressure balances in a seal which has  pressure from both sides,  thus it doesn’t have the loading in which the seal that only sees pressure from one side.  UEA will offer guidance when designing hydraulic swivels to reduce negative effects of uneven seal loading, as well as pressure limitations.


High temperatures (those at or above the materials limit) tend to soften the material (plastics) and this could lead to increased wear; the wear rate of the material will typically increase as the temperature increases.  Additionally, high temperatures tend to harden rubber materials and helps them take a compression set, thus reducing the seals interference and reducing its life.  Cold temperatures don’t usually affect the life of the seal, however depending on the materials used, leakage issues could result from cold temperatures.  Temperature limits are discussed with our potential customers to eliminate temperature-induced problems.  UEA does not have temperature issues within the construction and related industries.

Fluid Compatibility

Depending on the reaction between the material and fluid, if it is incompatible, the conditions found are swelling and softening of the material.  There can potentially be major interactions in which the material completely breaks down and the seals fail. For example, most urethane materials used in sealing can undergo hydrolysis, in which hot water breaks the urethane down.  The result is a seal that is very brittle and it crumbles.  Swivels supplied by UEA will not have compatibility issues.  We require our customers to describe the material that will be flowing through the hydraulic swivel.  If a customer wants to put some substance through the swivel that is out of the ordinary, UEA will discuss the situation with our seal supplier and formulate a solution.


It’s usually the lack of lubrication that has a negative effect on the seals.  As lubrication helps to reduce the friction, also reducing heat buildup, the seal will last longer.  Not enough lubrication has the opposite effects and would typically cause the seal to wear faster.  The cap seals used in UEA swivels have lubrication grooves that allow rotary lubrication.  Our cap seals also have side wall notches that allow increase seal shifting speed, which eliminates rare occurrences of a seal bypass situation.


Contamination or debris in the hydraulic system can have negative effects on seals.  They act as an abrasive to the sealing components and hardware, and can abrade the seal and/or damage the hardware.

UEA takes contamination seriously.  Our swivels are assembled in a pharmaceutical grade clean room.  This keeps foreign material from entering the swivel during assembly.  We utilize excluder-type seals on both ends of the swivels, this eliminates contamination entering the swivel from the ends.  We also plug all ports with port plugs before any swivel leaves the clean room, eliminating any intrusion through the ports.  Our test oil is constantly monitored with a laser particle counter and meets the ISO standard 18-16-13.  Contamination will not be an issue with UEA supplied hydraulic swivels.


The higher the speed, the more internal heat buildup the seal will have.High rotational speeds can lead to localized high temperatures that have a negative effect on the seals.  As with hydraulic cylinders, the contact point is usually moving, so the area in which the heat must dissipate is much larger.  It is advantageous to have continual oil or fluid movement within the swivel to help dissipate the heat.  The larger the swivel diameter,the slower the max speed; not surprisingly, the smaller the swivel diameter, the faster it can spin.  Depending on size, UEA will recommend a max speed.  We have not had any situations where the speed has been limited by our seals within the construction/forestry and related industries. There are many more issues that can  negatively affect swivel performance.  Open communication between all parties is vital in creating a custom, long-lasting solution to your swivel requirements.  We pride ourselves in having industry leading customer service, in which quick and open communication is key.  We would love the opportunity to quote your next project requiring hydraulic swivels with or without electrical slip rings.

For further information on Hydraulic swivels, check out our blog regarding the custom swivel design process.

Brady Haugo
Senior Design Engineer

How Does UEA Work with Customers?

November 2, 2016

Over the years there have been a multitude of successful, long-term partnerships with some famous pairs in the entertainment field such as Laurel and Hardy, Abbot and Costello, Dean Martin and Jerry Lewis among others.   These partnerships were successful for many reasons, but one reason was the fact that each of the partners played a specific role suited to their specific talents.

At UEA we like to form partnerships with our customers using our expertise with electrical slip rings, cable reels, hydraulic swivels and shift controls in conjunction with our customers’ superior knowledge of their markets and actual working environments to design and build the products that meet or exceed their expectations.

Recently we were contacted by a customer of many years concerning a problem reported from the field.  In this situation the UEA product involved a shift control and the problem was a loosening of the screws retaining the shift lever to the switch drive bearing.  After a brief review, it was determined that although not a problem with most of the shift controls sold by UEA, in this instance the application involved a very high vibration environment for many hours per day.

UEA’s first suggestion was to switch from a medium strength Loctite Threadlocker.  Testing was done to verify that the screws could still be removed if necessary without adding heat.  The second suggestion was to slightly increase the torque specification from 30 to 35 in.-lbs. during the installation of the screws using a regularly calibrated torque wrench.

Both suggestions were approved by the customer and the new specifications have been added to the work instructions.  Field testing will be used to validate the success of the improvements, which were added without any cost increases.  If other revisions are required in the future, UEA is here to work with our partners to help solve their problems as they may arise.

In this case the customer, and partner, was happy to have someone respond to their problem and work with them on a solution.   Webster’s Dictionary describes a partnership as a sharing and that is what we always hope to do.  When our customer shares their needs and problems with UEA we will use our knowledge, gained through more than 60 years of operation, to solve their problem and meet their product needs.  Thus a partnership is formed.

For more information about UEA working with customers, visit our blog.

Brent Jensen

Senior Project Engineer