A low-friction seal system that can be readily adapted to existing triaxial cells has been developed. The system provides negligible friction correction for dynamic testing as well as long-term creep testing. The design principle of the Hydrostatic Seal System I is based on providing axial guidance of the piston rod with two "Thomson" ball bushings and utilizing a slow leaking air seal by a close-fitting floating seal. The water level is maintained in the chamber between the two ball bushings and the air pressure is applied at this interface. The seal consists of 3 components: fixed brass ring, brass bushing, and spring. The friction is low and repeatable because the rigid material used for the seals do not change appreciably with pressure, setup time, or deformation rate. In the Hydrostatic seal system II (which requires less machining) the ball bushings have been set in resilient mounts that allow for some tilting of the bushing; thus all balls share in carrying of load as opposed to a single ball taking most of the lateral load. Heat shrinkable tubing or adhesive tape is used to close the space between the ball bushing and the "seal" bearing, and also hold up the air-seal when there is no chamber pressure. Since the tubing or tape is not rigid, lateral movement of seal is still possible. The first system using custom made parts could give a lower friction; however, friction values on the 2 systems are comparable if care is exercised in the matching process. Currently, rod sizes being used successfully with this system include 3/8 in., 1/2 in., and 3/4 in. in triaxial cells as well as back pressure consolidometers.

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Filing Info

  • Accession Number: 00127113
  • Record Type: Publication
  • Report/Paper Numbers: ASCE #11538 Proceeding
  • Files: TRIS
  • Created Date: Dec 29 1975 12:00AM