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At hydroelectric plants, different types of wooden structure~ are built in zones where the water level varies, with the result that the wood rots and the useful life of these structures is reduced. Considerable quantities of wood are used each year for repair work of which a sizable portion is irretrievably lost.At the Vuoksinsk cascade, steel was successfully used instead of wood for the drift barrier, the scaffolds under the turbine runners, and formwork for the reconstruction of deteriorated concrete. This measure proved to be economical as regards the initial expenses and permitted reducing the maintenance personnel. Drift Barrier on Steel BuoysA barrier supported on steel buoys, which was built according to a design prepared by the operating personnel of the cascade, has been operating successfully since 1967 at the Lesogorsk hydroelectric plant (Fig. 1). The barrier sections consist of welded steel frames supported on five steel buoys of 1.2-m diameter and 0.6-m 3 volume (Fig. 2). A wooden deck on the frame serves as the operating bridge along the entire barrier.

Repair of runner-blade seal. Replacement of the leather runner-blade seals of adjustable-blade hydromrbines is labor consuming, as it requires demounting of the removable section and bIade of the runner. Hydroturbine operating experience atLen4nergo (Leningrad Regional Administration of Power System Management) sequence No. 1 showed that, depending on the quality of the leather, blade seals serve from 3 to 15 years (seals of elk leather have a longer service life).Identical damage has been observed during replacement of the seals of 24 blades of six hydroturbines with capacities of 25-27 MW: the bronze spring washers are deformed and lose their elasticity with long-term operation; and the leather becomes soaked and wears away on the water side. On the side away from the water, deep radial and peripheral imprints and cuts from the spring washers are noted. The edges of the leather washers are cut around their entire circumference and partially torn.Operating personnel replaced the leather seals of four bla des of one turbine with rubber. The experimental seals ( Fig. 1) are made up in a package consisting of an oil-resistant rubber ring of average hardness and 6 mm thickness, a washer of two pieces of brass foil cemented together with a 0.2 mm thickness, two bronze spring washers of 0.5 mm thickness, and three rubber washers of 0.7 mm thickness. The rubber ring was covered with foil, with small outlets along the diameter to prevent cutting of the rubber by the spring washers. During assembly of the seal package,the rubber ring and foil were abundantly lubricated with thick grease. To improve the lubrication of the rubber ring, two 12 mm holes were drilled in the blade flanges. The seal cavity is packed with grease once a year. The threaded part of the opening is closed with a plug.After insrallation of the seal, tests for watertighmess, and 300 rotations of the blades, the seal was dismantled and inspected during unwatering of the draft tube. No breaks were observed in the surface of the rubber. Leakage of oil through the blade seal after 2 years' operation had not changed and remained within normal limits.Favorable experience with the operation of rubber seals demonstrates the feasibility of replacing leather seals with rubber without changing the design. To increase the service life of the seals, it is necessary to place brass foil under the bronze spring washers in order to prevent cutting the leather or rubber by the edges of the spring washers, and periedieally to pack thick grease into the seal cavity through openings drilled in the blade flanges. iI y Fig. I. Runner-blade seal. i) Blade flange; 2) rubber seal ring; 3) brass washer; 4) bronze spring washer; 5) rubber washer; 6) lubrication openin~ with plug.

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