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It has been established experimentally and confirmed analytically that before the stall of a centrifugal impeller pump, self-oscillations (surging) of the pump are set up in the region of ascending cavitation branchings of its monotonically decreasing head characteristic. Beyond this region, the pumping mode of such a pump is absolutely stable. It has been established that changes in the nonstationary operation of a centrifugal impeller pump produced by variation of its wave resistance are diametrically opposite in character in cavitation and cavitation-free modes. Introduction.It is well known that the reason for excitation of longitudinal self-oscillations (surging) of impeller pumps is the formation of an ascending branch on their head characteristic H(Q) [1]. In the case of the nonstationary operation of an impeller pump, unlike a compressor, elimination of lumped air caverns (volumes) in the hydraulic system leads to such a marked decrease in the amplitude of self-oscillations of the pump that it becomes possible to experimentally determine the ascending (unstable) branch of its head characteristic and the cavitation branchings of this characteristic H(Q, Δh). Also, it is known that in hydraulic systems, self-oscillations are set up before the failure (stall) of an impeller pump [2]. In the operation of a screw centrifugal pump feeding the propellant components to a liquid-propellant rocket engine, i.e., of a short-life pump, self-oscillations of such a pump are excited even in the absence of the ascending branch on its head characteristic. The setup of self-oscillations of a screw centrifugal pump with a stable monotonically decreasing head characteristic has been investigated with a number of models in [3] and the operating mode of such a pump due to the setup of the so-called "cavitation" self-oscillations has been considered. A nearly stall pressure is often taken as the permissible inlet pressure of a centrifugal impeller pump with a short life [3,4]. It is stated [3, 5] that cavitation self-oscillations cannot be set up in modes similar to cavitation stall where the pump operation is unstable. In [6], it is assumed that cavitation self-oscillations are characteristic not only of centrifugal impeller pumps but of screw centrifugal pumps as well.Experimental investigations of a centrifugal impeller pump with a monotonically decreasing head characteristic [7] have shown that before the stall where the head of the pump is dependent on both the volumetric rate of water flow Q and the pressure on the pump inlet P in , the characteristic H(Q) branches out. Surging occurs in the region of the ascending cavitation branchings of this characteristic H(Q, Δh), where the derivative is ∂H ⁄ ∂Q > 0, and self-oscillations are dependent on the reactance of the oscillatory circuit. Thus, the setup of oscillations of the centrifugal impeller pump before its stall is attributable to the surging in the region of ascending cavitation branchings of the pump's head characteristic. We were unable to find experimentally cavitat...

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