In most applications that use hydraulic swivels, the parts of the swivel that wear the most quickly are the seals. Therefore, 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.
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.
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.
Senior Design Engineer