In general, the sealing principles of X-rings are almost identical to that as O-rings. Sealing is achieved with radial squeeze in a piston/bore type gland. Additionally, the same design characteristics such as stretch, squeeze, and volume fill should be considered. While the overarching principles may be the same, there are some distinct advantages to using an X-ring in a dynamic application as opposed to an O-ring:
• X-ring groove should be designed deeper than O-ring grooves. This allows sealing to occur with less overall squeeze and, therefore, less overall friction.
• The four lips of an X-ring create a notch which retains lubrication
• Due to the design of the profile, X-rings are not prone to spiral failure in reciprocating applications. This is the largest advantage X-rings have compared to O-rings in dynamic applications.
In addition to what was previously mentioned, there are some additional design considerations when creating a reciprocating gland for an X-ring. For one, it is recommended to use the largest possible cross section of X-ring due to the fact that larger cross sections can handle a wider range of tolerance variance. This allows for sealing in a much wider range of dimensional variation in both the mating hardware and the X-ring.
X-rings can also be used in rotating glands, even though reciprocating glands are where their advantages really shine. When designing an X-ring in a rotary gland, just like with O-rings, it is always recommended to design the X-ring as a female seal. X-rings work best if the rotational speed is kept below 6.5ft/s, the pressure is below 150psi, and temperatures are within -30°C – 100°C. X-rings in rotary seals should also be made of 80 or 90 durometer material.
|While X-rings do have many advantages in dynamic applications, there are some cautions to using X-rings in dynamic applications. Since the groove is designed deeper than an O-ring groove, standard backup rings will not work in an application with X-rings. A custom backup must be used if it is required for an application. In rotary seals it is also important to make sure the surface finish of the spinning rod is smoother than the groove. This will help prevent the X-ring from spinning with the rod and staying in the groove.|