# Research on the High Speed of Piston Pumps Based on Rapid Erecting of Launch Vehicles
## 1 Introduction  
Modern warfare is fast-paced and high-intensity, and mobile launch faces the threat of all-around reconnaissance and long-range precision strikes. Therefore, preparation time before missile launch must be minimised [1]. Rapid erection, a phase in preparation for missile weapon launch [2], has become an important research direction to improve the launch system's rapid response ability and manoeuvrability, which is crucial for enhancing the mobile weapon combat system's survivability. hydraulic system due to the limited space of launch vehicles [9]. It is necessary to increase the rotational speed of piston pumps in order to achieve rapid erection. However, high-speeding increases cavitation in the piston chamber [10; 11; 12; 13], slows the filling rate of piston pumps [14] and lowers volumetric efficiency. This causes the flow rate to increase slowly or even drop when rotational speed is increased. Cavitation will also aggravate flow pulsation and increase the vibration and noise of the system, which is detrimental to the hydraulic system's stability. At the same time, the backflow will happen when the piston chamber and suction and discharge oil unloading groove of the valve plate come into contact. Backflow will not only cause cavitation and damage the wall, but it will also increase flow pulsation, which is not conducive to the efficient and steady working of the system. In order to improve volumetric efficiency and reduce flow pulsation, the cavitation phenomenon in the piston pump must be suppressed [15; 16]. In an axial piston pump, there are two types of cavitation: (1) Vaporous cavitation: When the pressure of hydraulic oil falls below the saturated vapour pressure, the medium gasifies. (2) Gaseous cavitation: When the pressure is lower than the air separation pressure, the dissolved air precipitates from the oil, and there is no phase change. When vapour bubbles collapse, they not only reduce volumetric efficiency but also hit the inner wall of the pump, exacerbating the pump's vibration and noise. Although the gaseous bubbles have no effect on the pump body when they collapse, it is the primary cause of volumetric efficiency reduction. Nowadays, the main measures to prevent the cavitation of piston pumps include installing booster pumps at the oil suction port [17] or booster impellers to increase the inlet pressure [18]; lowering the inclination angle of the swash plate [19]; using capped pistons [20]; optimising the size [21], shape and the number of unloading grooves [22; 23; 24; 25]; topology optimisation of the suction duct [26]; using inward or outward inclined cylinder waist bores to allow oil to be drawn in by the centrifugal force generated [27]; optimising the structural parameters of the waist-shaped bore in the window area of the cylinder [28]. However, the adoption of booster pumps or booster impellers will increase the size of the hydraulic erection system, which is incompatible with the limited space of the launch vehicle. Although the cavitation of piston chambers can be suppressed by reducing the swash plate angle, the theoretical flow will be reduced. In summary, there are several studies on the cavitation of piston pumps and cavitation suppression. One of the key directions of research is to optimise the waist-shaped bore of the cylinder to suppress cavitation. Previous studies have only focused on the improvement of the inclined waist hole and the optimisation of the structural parameters of the waist  
Figure 1: Diagram of launch vehicle erection. hole cross-flow surface [27; 28]. However, there are few publications on the suppression of cavitation and enhancement of piston chamber volumetric efficiency by improving the overflow surface in the window area of the cylinder at high speeds. As a result, it is vital to study the high-speed design and cavitation suppression of a high-pressure axial piston pump from the perspective of the design of the overflow surface in the window area of the cylinder.