Experimental Analysis of Flow Through Throttle Valve During Gaseous Cavitation

Abstract

The multiphase flow in oil hydraulic systems has a very significant effect on the correct operation of the hydraulic system. Air can be found in various states in hydraulic systems, while free entrained air in the form of bubbles has the potential to be the most problematic. It especially affects the compressibility of the hydraulic liquid resulting in reduced stiffness of the hydraulic system. The actuators of the hydraulic mechanisms then do not achieve the fast response and the precision of movements depending on the input control signals. One possibility for the contamination of hydraulic fluid by air bubbles is through a phenomenon known as gaseous cavitation. This is a phenomenon in which gas is released when the pressure drops below the saturation pressure of the dissolved gas in the liquid. This article focuses on the experimental analysis of the flow through the throttle valve which is affected by the formation of air bubbles at the throttle edge of the valve. The regions of gaseous cavitation were observed at the different flow cross-section of the throttle valve. The throttle valve was placed into the block of transparent material to provide visualization of the individual measurements. The article is supplemented with photographs of the individual measurements showing the gaseous cavitation inception. Research background: flow cross-section, cavitation phenomenon, discharge coefficient. Purpose of the article: Effect of flow cross-section size and flow velocity on cavitation development. Methods: Experimental measurements. Findings & Value added: The investigation of the gaseous cavitation inception, Visualization of the individual measurements.

Identifying regularities of fluid throttling of an inertial hydrodynamic installation

“…Many studies are devoted directly to the physical phenomena occurring during throttling. Work [4] is devoted to the experimental analysis of the flow through the throttle valve, which was affected by cavitation, namely air bubbles formed in the liquid. Where the amount of dissolved gas in the liquid is directly proportional to the partial pressure of the gas in the liquid, which is determined by Henry's law.…”

Effect of Cavitating Hydraulic Elements on Pump Characteristics

“…The prevailing low pressure of the liquid rises as the vapor pockets traverse the impeller blades. The rising pressure causes the vapor pockets to collapse against the impeller and pump housing, producing noise and damage of cavitation [14]. We can improve the NPSHA by either increasing the suction static head above the pump centreline and the pressure above the liquid in the suction tank or by reducing the losses on the system suction side, which subtracts energy from the liquid.…”

“…Cavitation can be identified acoustically [4,18], by vibrations [19], visually and by measuring hydraulic characteristics [4,8,14,15]. An overview of cavitation detection in pumps is given in [20,21].…”