Development And Testing Of A Very High Speed Oil Lubricated End Face Mechanical Seal.

Abstract

Six large radial inflow turbines were designed to expand isobutane for two electric power plants in Nevada which use heat from the earth (geothermal energy) as the energy source. Double end face mechanical seals lubricated by oil were selected to stop the isobutane from leaking out of the closed loop system and into the atmosphere. Two of the largest providers of mechanical seals in the world provided reference lists showing that this application was pushing the tip speed limits for existing liquid end face mechanical seals. A vendor was selected and the seals were purchased. The first run of the seals on the test stand seemed successful, until the disassembly of the unit revealed the faces were severely overheated and heat checked. The face design was changed and the second test was successful. A major concern was to maintain a low seal leakage rate, so this was measured and was within the specified range. However, the third test resulted in a catastrophic failure of the rotating faces and collateral damage to the entire seal cartridge. Detailed investigation of the failure revealed several interesting problem areas. All of these were addressed in a new design which was implemented, built, and shipped in only one week! The fourth test was successful, but still showed a problem in which the very high velocity oil in the seal chamber was able to dislodge the stationary face retaining ring. A solution to this final problem was implemented and tested successfully. At the time of this abstract, the seals appear to be successful. Both plants (all six machines) have been placed on line successfully. Two seals experienced damage in the field due to problems with the lube oil filter housings. These problems will be discussed during the presentation.