Troublesome oil leakage eliminated at Truman plant
During the planning stage of the Harry S. Truman Dam and Reservoir in 1962, the design was modified to include a six-unit, 180 MW hydroelectric power plant. An initial analysis of the Warsaw, Mo., site detected massive bedrock at the tentative powerhouse location. A slant axis design, with turbines installed at a 24-degree angle, was selected over traditional vertical designs, in part, to eliminate additional excavation, minimize development costs and incorporate pump-back capability into the redesign.
A long-term problem for the plant was excessive oil leakage at the seal interface between the oil-head assembly and the runner hub. The leakage was creating an increase in turbine maintenance and hampering manpower availability on other activities. “Environmental issues are a major consideration when dealing with oil systems,” said Michael Scott, Corps of Engineers mechanical engineer and technical coordinator. “The leaked oil must be collected in a sump, then pumped into a holding tank and purified before reuse.” The original seal design was a three-ring square packing. A multisectional carbon seal was installed in an attempt to eliminate the leakage, but it did not provide sufficient sealing. The hub holds 900 gallons of turbine oil under a normal operating pressure of 25 psi.
Convinced that effective sealing could be achieved, the Corps solicited, in April 1994, a number of design proposals and assembled a team dedicated to the power plant`s operation. “When the manufacturers provided their own design recommendations, each team member evaluated the proposals on his own,” said Scott. The Advanced Products (AP) recommendations were adopted.
The AP seal is a cartridge assembly composed of five machined assemblies and two 18-inch AP EnerSeals. With the cartridge design, the seals install axially and run on the oil pipe extension on a chromed steel surface. Oil pressure is applied to the cavity between the seals so the first seal is floating. Hub oil pressure is applied to the cavity through a fail-safe orifice that limits the oil leakage rate if the external side seal should fall.
The FLO Mark IV Flanged Axial Dynamic EnerSeals are engineered with a filled Teflon jacket made resilient by a high-grade, internal spring that ensures positive sealing in environments where other seals can leak. The EnerSeal jacket is enhanced with low-friction and strength-enhancing additives and is suitable for pressures to 3,000 psi, 21 megapascal.
AP created a prototype for the Truman plant`s Unit 3, which now has more than 1,800 successful generation hours. Six additional assemblies were delivered to the plant in October 1996.