Ring seals are used in rotating union applications where a fluid flow or hydraulic pressure signal is transferred from a static reference frame to a rotating component, such as a shaft, for the purpose of providing lubrication and/or a hydraulic signal to a component(s) in a rotating frame of reference. Ring seals are used in physically compact configurations.

Ring seal performance is limited by the pressure of the fluid that is to be sealed, the resulting contact pressure, and the relative tangential speed that the ring seal contact area is subjected to. Excessive pressure and speed will cause increased power loss, premature wear, seal leakage, and eventual seal failure. In application, the use of rings seals is limited by fluid pressure and tangential speed of sealing area.

The duplex-ring seal configuration permits a significant increase in machine shaft speed by reducing the effective tangential velocity of the seal element contact area to approximately 60% of the original. For a given application, this configuration can permit increased machine rotating speeds of up to 170%. In addition, substantial increases in durability and service life can be realized.

The reduced-speed duplex-ring seal arrangement decreases the relative tangential velocity of the sealing element by introducing a second larger and concentric seal, and a gear-driven intermediate stator ring that serves as both the outside diameter to the original ring seal and the inside diameter to the second added larger concentric ring seal. The intermediate stator ring is driven by a speed-reducing gear assembly directly from the machine shaft. By optimization of the gear drive ratio, both seals are at approximately the same tangential speed, and probable equal service life. Ring seal performance is limited by the pressure to be sealed, the speed of the rotating element, and net pressure and relative tangential speed to which the ring seal contact area is subjected.

The seal arrangement provides a potential reliability and life improvement for a necessary integral rotary hydraulic feed-through component required as part of the development of a variable-speed transmission for advanced rotorcraft applications. The unique configuration of the transmission coupled with high-speed (15,000 rpm) shaft operation requires a compact, high-speed rotary seal not readily available in the open market. The mission profile of the machine is 90% service life at 1 MPa at 7,500 rpm, and 10% service life at 0.55 MPa at 15,000 rpm. The ring seal configuration offers a viable solution for sealing a necessary component of the example rotorcraft drive system, that of providing a seal from a static to rotational reference frame for fluid flow and a hydraulic signal, and permitting ring seal operation for the high-speed portion of the mission, and significantly increasing ring seal service life for the low-speed portion of the mission.

This work was done by Mark A. Stevens, David G. Lewicki, and Robert F Handschuh of Glenn Research Center.

Inquiries concerning rights for the commercial use of this invention should be addressed to

NASA Glenn Research Center
Technology Transfer Office at This email address is being protected from spambots. You need JavaScript enabled to view it..

Refer to LEW-19224-1.


NASA Tech Briefs Magazine

This article first appeared in the April, 2015 issue of NASA Tech Briefs Magazine.

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