BASIC DIRECTION OF THE IMPROVEMENT OF GATE SEALS IN HYDRAULIC STRUCTURES UDC 62.762.8:627.845.004.69

G. A. Polonskii

Hydraulic-gate seals are highly important elements. When the seals in gates at hydroelec=ic plants operate tmsatisfactorfly, water is lost from the reservoir and the electric energy output may be reduced. Defective seals in maintenance gates complicate, and sometimes make impossible, unwatering of the protected space, with the result that the maintenance work is slowed down. Low-qnality seals in temporary gates used during construction slow down the carrying out of the construction work. In many cases, leakage through gates causes them to vibrate. Under freezing temperatures, at the leakage spots in surface gates ice covers are formed at times, which make the operation of the gate difficult and may lead to damage of the hoist and the gate itself (Fig, 1). While, in low-head structures, leakage through the seals leads to waste of water, in high-head gates it may also cause slit cavitation, as a result of which the seals are quickly destroyed and vibrations and hydraulic impact are caused. One of the causes of vibration may be the infiltration of water between the upper horizontal seal and the upstream wall. To prevent the vibratiom, and also to protect the seal, the upstream wall is usually strengthened by means of a steel lining as high as the operating travel of the gate. In this design, the seal did not come away from the lined surface of the upstream wall. It is possible to reduce the height of the upstream wall, to diminish the load on a low-head deep gate under partial opening, and to ensure continuous action o f the upper seal in modern gates by using seals consisting o f several horizontal elements, * the distance between which is less than the operating height of the lining of the upstream wall. Figure 2 shows a v e r t i c a l - l i f t fiat gate in which the movable part of the gate 1 is equipped with several horizontal seals 2, located on the skin plate parallel to the upper horizontal seal 3 and the lower seal 4 at equal distances l~, which are somewhat smaller than the operating height of the lining and may be several times smaller than the operating travel of the gate. This design ensures relay action of the horizontal elements; that is before the break of contact between one of the elements and the lining, the i m m e d i a t e l y higher or lower horizontal e l e ment comes into contact with the lining (depending upon the direction of the gate displacement). This principle may be adopted for all low-head, vertical-lift deep gates operating in intermediate positions in spillways and sluiceways. In the case of several horizontal elements in most of the intermediate positiom, the gain transmits a smaller load: this make it possible to provide better protection for the supporting-traveling and embedded parts, to eliminate gate vibrations, and to reduce wear of the seals, The use of relay seals at the Lenin's Young Communist League Saratovsk hydroelectric plant and reduction of the height of the linings on the upstream beams made it possible to save 905 tons of steel and 4586 m3

Fig. 1. Formation of ice covers at leakage spots in surface gates.

*O. V. Malyarevskii, Author's Certificate No. 160990 (USSR). Published in Byulleten" Izobretrenii i Tovarnykh Znakov, No. 5 (1967).

Translated from Gidrotekhnicheskoe Stroitel'stwo, No. 3, pp. 15-23, March, 1973. 222

IMPROVEMENT OF GATE SEALS IN HYDRAULIC STRUCTURES

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,4 I---Fig. 2. Gate with relay seal. of concrete. In cost terms, the saving obtained from the use of gates with relay seals amounted to 289, 000 rubles. For high heads, the sealing elements should have adequate deformability, mechanical strength, cavitation resistance, and elasticity. The last property should ensure adequate covering of all the irregularities in the sealing surface so that no water leaks through them. Important work relating to the development of sealing elements for high-head gates has been carried out by the Mosgidrostal'Special Design Bureau of the Gidromontazh All-Union Trust jointly with the Sverdlovsk Factory of Rubber Products, which is the manufacturer of the seals. In the design of v e r t i c a l - l i f t and, especiaUy, segmental deep regulating gates for the Charvaksk and Nurekskhydroelectric plant, it was found that none of the sealing e l e ments known by that time (Types I-IV) had properties or technical characteristics corresponding to the requirements placed on these elements. In this connection, it became necessary to plan and carry out extensive investigations in order to design the required type of sealing element and to develop techniques for its manufacture, erection, m a i n t e nance, and expeditious operation. During a given service life. this sealing element should perform its function by taking into consideration possible inaccuracies in the manufacture and erection of the g a t e the embedded parts, and the seals themselves; mechanical, thermal, and residual deformations in the gate and the embedded parts; and wear of the seal and of the supporting-traveling parts. The techrtical characteristios of the seals and recommendations for their use are summarized in T a b l e 1. Taking into account the large friction forces produced on the surface of the seal and the high velocity (up to 40 m/sec) of the water which infiltrates during operation of high-head gates, it is found necessary to prevent the

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the Charvaksk plant~ at the design bureaus of the Gidromontazh trust there was disagreement concerning the selection of the type of seal for the high-head segmental gate, and it could be confirmed only that installation of the seal in the movable part of that gate could not be considered a rational measure since it is necessary to use an upstream beam with a continuous curved steel lining, with the result that the seal on the sillhas a short life owing to location in the zone of high-fiow velocities. In order to develop a sealing element for a deep gate at the Nureksk hydroelectric plant, which hasopening dimensions of 5 • 6 m and an eccentric support subjected to a head of 110 m, the mechanical laboratory of the MosgidrostaI" Special Design Bureau established the shape and the transverse dimermi~ of the seal. and eliminated also the elastic and relaxation characteristics of the rubber element. The main criteria for evaluation of the design of the sealing element were the results of repeated tests of seals having full-scale cross-sectiona~dimensions. All the samples tested were prepared by mechanical treatment from a solid rubber slab over 250 m m thick. Before development of the final shape and dimensions of Type VI sealing element, 40 different seal sizes were made and tested. Simultaneously with development of the seals, the investigators worked out methods and means for experimental investigation and determination of the properties and characteristics of the developed seals, which were made from 800-ram long strips with full-scale, cross-sectional dimensions, as well as from closed and channel elements measuring 1.5 • 1.5 m. Considerable attention should be focused on the development of a formula for rubber mixes and of preparation techniques for seals in specially designed and manufactured press forms. The formula for the rubber mix for a closed-contour, Type VI deformable seal, installed in the embedded parts of a gate at the Nureksk plant, was selected following tests on over 20 straight strips made by using five different formulas for rubber mixes. As a result of tests on different types of rubber, it was found that the best properties are possessed by rubbers prepared from natural caoutchouc and having a hardness of about '/0 units in the Shore hardness scale. These rubbers have the required rigidity and strength as well as a very small stress relaxation and a m i n i m u m creep under prolonged loading. During watertighmess tests on the seals under a head of 110 m, it was found that they were watertight when compressed to 7 ram. To verify the effects of cuts or poorly vulcanized joints, tests were carried out on a seal with a slit in a joint over the entire cross-sectional area and a slope of 1: 10. This seal was watertight when compressed to 12 ram. Its strength and cavitation resistance were verified on a special stand. As a result of the investigations, it was possible to design the strengthening elements of the seal and to determine the shape which would permit the seal to operate under the hydraulic head with an artificially made slit for

about 250 h without any visible damage. Deformable seals were adopted for the segmental gates at the Point d a m in the USA and the Futazi d a m in Japan, after the specialists determined that the hydraulically-controlled seals installed in the skin plate of the gate were excessively complex and unjustifiably expensive. The successful use of a deformable seal made it possible also to ensure radial displacement of the gate by means of eccentric supports. For the high-head segmental gates at the Nureksk plant (Fig. 4) an advantageous type of seal was a deformable seal (Type Vl). which operates on the basis of the principle of waterproofing of the joint between the gate and the embedded part by pressing the span frame of the gate against the seal installed in the embedded part. In this case, for radial displacement use is made of a hydraulic drive of medium capacity, and simpler seals and embedded parts are obtained. The waterproofing depends only upon the magnitude of compression of the rQbber seal, which is determined exactiy by the regulated travel of the stem of the servomotor. This is very important for ensuring the required efficiency of the gate installation. Good waterproofing is favored also by the following constructional characteristics of deformable seals: since they operate under compression in order to make the joints watertight, they seal reliably the possible irregularities, which are especially dangerous in the case of slit cavitation and erosion. With partial opening of the passage, the portion of the seal adjacent to the skin plate of the gate is compressed and restrained, while the lower portion does not become stressed and remains elastic, so that the possibility of its being damaged is very stoat1; the high strength and friction properties of the rubber seal permit obtaining high friction forces in the zone of contact with the skin plate which, in combination with the forces developed by the servomotor of the hydraulic drive, keep the gate stable in all possible operating positiom and protect the seal against wear.

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Since the seals are monolithic, in the case of sufficiently large transverse dimensions and rigid supports, they exhibit excellent hysteresis properties and may perform successfuUy the functions of shock absorbers, thus reliably protecting the movable element against dangerous vibratiom, developed when the passage is partially opened. Owing to the simple construction of these seals, the vulcanization of the joints during assembly, their adjustment, instaUation, and replacement do not involve any difficulties. In contrasL in most of the known types of seals, the main rubber elements almost always operate under tension, which is not always desirable. For the emergency vertical-lift, crawler-mounted gates at the Nureksk plant, which were to cover large openings measuring 3.5 x 9 m, under a head of 110 rn. it became necessary to develop another type of seal. Prior to the design of these gates, laboratory hydraulic and mechanical investigatiom were carried out. Tests on the seals permitted establishing their watertighmess conditions, the amount of deformation under the design heads, and the elastic characteristics required for determining the values of the reactions and of resistance to gate displacement. As a result of these investigations, a sealing element (Type VII) was developed for emergency gates operating under heads of 120 rn. This element for the vertica1-1ift, roUer-supported, emergency-maintenance gate at the Nureksk plant is instaUed in the skin plate of the gate, that is, on its water-retaining side, and has a channel contour. It is intended not only to cover the gap and to waterproof the joint between the skin plate of the gate and theembedded parts of its groove element, but also to support the gate in the grooves, mainly for full opening of the flow passage. The sealing element may be deformed to a thickness of 10 ram, may cover a 7-ram gap, and may waterproof the joints in the sealing contour by means of pressure from water in the operating chamber, this pressure being equal to the head required for obtaining a minimum compression of 3 m m in the seal. In order to reduce the resistance created by the sealing elements when the gate moves under the applied head, the upper end of the seal is lined with brass strips. However, the brass strips complicate the manufacture and instaUation of the seals. With high-quality assembly, adjustment, and hot vulcanization of the seal joints, l e a k a g e may be practically eliminated. For this purpose it is necessary that all the bolts in the planks through which the rubber is attached to the gate or to the embedded parts be firmly tightened without any bolt or spring washer being left out. The seal corners are weak spots of the gate instaiIation; for this reason special care is taken in their preparation. The connection between horizontal and vertical rubber seals should not be at a right angle. This type of joint requires an exceptionaUy exact cutting of the rubber, and presents considerable difficulty. Moreover, even after a careful adjustment, leakage through such joints is Observed. The joints in the rubber seais should be located in a straight portion. Rubber seals should not be bent at a right angle since on the internal sides of the angles wrinkies are formed which inhibit the close contact of the rubber, while on the external sides of the angles cracks are produced. These defects may be eliminated by preparing the corner portions in special compression molds at the factory. After completion of the hot vulcanization, the seats of high-head gates should b e subjected to hydraulic tests. In present-day hydraulic construction it is urgently necessary to develop high-head gates of sufficient capacity for covering large openings, for withstanding large loads, and for preventing the passage o f water through the seais. For the Sayano-Shnshensk. Ingursk, and other high-head hydroelectric plants, the Scientific-TechnicaICouncil of the Gidromontazh Trust examined in 1971 the design work carried out by the LengidrostaF and Mosgidrostal' special design bureaus, in connection with the d e v e l o p m e n t o f a vertical-rift sliding gate with supporting-traveling parts made from butytate, for a head of 180 m, a tubular g a t e " for a head of 180 m, and other types of gates for operation under heads of 180-200 m. For these gates, it is necessary to use seals having other geometrical shapes and made from materials different from rubber. Conclusions. 1. In recent years, a large volume of work has been carried out in connection with the d e v e l opment of new types of sealing for operation under heads o f up to 120 m. 2. The operation of deep segmental gates at the Charvaksk hydroelectric plant over a period of two years confirmed the satisfactory functioning of the sealing elements of deformable-hydraulic action. *V. Ya. Koshkin, R. M. Tokhtas'ev, V. A. Voznesenskii, and S. V. Seleznev. Author's Certificate No. 312916 (USSR). Published in Otkrytiya. Lzobreteniya, Promyshlennye Obraztsy. Tovarnye Znaki, No. 26 (1971).

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3. The operation of deformable seals has been comprehemively studied under laboratory conditiom and such seals are now imtalled at the Nureksk hydroeleclzic plant. 4. For high-head gates operating under heads of 150 m and over. it is necessary to continue with the work relating to the development of new types of sealing elements.