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For major water-conveying and irrigation canals in gently sloping terrain, it has been found preferable to use pmnp stations with horizontal-axis units operating under heads of 3-12 m. The transient phenomena of these stations have several features, one of which is the relatively high rise in head at different stages of starting and stopping the pump under a head corresponding to the characteristic optimum. This circumstance causes an increase in vibration and dynamic loading and thd risk of unstable pump operation.The head rise above the design value during transitional regimes, together with other factors, is determined by the design of the discharge structure and the nature and form of the universal characteristic diagram of the pump.With regard to the fact that dynamic loadings on the pump unit during the transient phenomena rise by several times compared with working regimes and that the volume of constructlon-erectlon work on the dlscharEe structure can amount up to 10-15Z of the total for the whole statlon= a reduction in the dynamic loads on the unit and the volome of the discharge structure is very pressing. Possible alternative solutions of these problems will be examined for pumping stations of the Dnepr-Donhas (Donets Coal Basin) Stage 1 type (Fig. i).The starting operation of a horizontal axial pump delivering into a short conduit with a gate in the discharge structure can be nominally divided into three stages: 1--switching on the electric motor until the instant of synchronizatlon~ 2 --filling the gate forebay up to the design level of the upper pool (V UP) downstream of the gate; 3 --from the cu,a=encement of filling the gate forebay to the design level of the upper pool, up to full gate opening~ at this instant the pump operates under an increased head. Depending on the starting time and the rate of gate raising, the water may either accumulate in the gate forebay, flow under the gate, or spill over it. Fig. 2 are variations of the hydrotechnlcal parameters of pump OPG-220G during the starting operation. Presented inIn the first stage, over a period of 5-7 sec, the pressures on the suction and dellvery sides of the rotor (Psu, Pd ) drop considerably, falling to a minimum during synchronization of the motor. Pressure fluctuations on the delivery side of the rotor (2Ad) and the relative vibration of the rotor chamber (S/S o t) increase with the P rotational speed~ and reach a maximum at the instant of synchronization. As full-scale tests indicated, the maximum heating vibration depends little on the rotor-blade regulating anglei however= it tends to diminish at average angles of blade installation.The illustration also shows radial vertical vibration displacements of the stiffening ribs on the pump runner axis~ the vibration displacwnants of the chamber being greatest compared with the changed values at other points of the pump unit. The nature of the variation in chamber vibratlon is similar to that in pressure fluctuatlon~ and has the same blade frequency as the pressure fluctuation.~n the second...

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In connection with the development of irrigation and water-supply systems there has been an increase in the production of high-output axiaI pumps for heats up to 20-28 m, the diameter of which is supposed to be increased to 5-8 m in the near future. The increase of dimensions, unit capacity, and volume of pump production increases the requirements imposed on reliability, service life, energy, cavitation, and vibration indices, and selection of the most rational regimes of their operation. High operating indices for hydraulic turbines are also quite important.Cavitation erosion of the blades and runner case is a major shortcoming that was revealed during operation of axial pumps and turbines. The effect of cavitation is aggravated by the suspended load in the water. In most cases wear of the runner case and the ends and peripheral surfaces of the blades determines the overhaul period of the units.Intense development of cavitation in axial hydromachines is due to the considerable pressure gradient in the slot between the case and runner blade. This pressure gradient causes bypass flow from the high to the low pressure side. In connection with the poor, from the hydraulics' standpoint, form of the end slot bounded by the case surface and rectangular end of the blade the bypass flow is accompanied by pressure decrease and development of slot cavitation. The flow emerging from the slot, interacting with the flow moving along the blade, promotes the generation of an cavitating eddy near the back surface of the blade. This eddy, moving along the blade, causes destruction of its surface.A characteristic manifestation of the effect of such an eddy is wear of the back surfaces of runner blades of the Kaplan turbines at the Perepad hydroelectric station. Operation of the turbines for a year under conditions of in~ense abrasive action and cavitation led to nonuniform wear of the surfaces of the flow channel, which increased severalfold in the region of the slot. Inspection showed that the slot between the blades and case increased twofold, and the trailing edges of the blades were severly worn. A band of erosion up to 20-30 mm deep had appeared onthe back surface of the blades 50-100 mm from the end and parallel to it. Wear of the trailing edges of the blades at the place of emergence of this band on them exceeded considerably the wear of edges on other radii.Obviously, it is possible to reduce the intensity of cavitation of the ends and surfaces of the blades and runner case by regulating the movement and improving the hydraulics of the flow in the slot, or by preventing the vortex filament from touching the blade surface.Some foreign companies, including onesinJapan and Sweden,* in order to improve the cavitationindices of axial turbines install fins on the ends of the blades, which increase the width of the slot, reduce the pressure blade surface on the place where the slot flow meets the main flow.The cavitation investigations made by the authors on two-dimensional models of the slots showed that the origin of cavitation...