In hydraulic system, cavitation is a phenomenon in which rapid changes of pressure in oil cause the formation of small vapor-filled cavities in places where the pressure is relatively low. Once the pressure reduces to below the level of saturated-vapor at oil working temperature, a number of vapor-filled cavities would be generated promptly. As a result, a large quantity of air bubbles lead to a discontinuation of oil in pipe or hydraulic elements.
The phenomenon of cavitation usually happens at the entrance and exit of valve and pump. When oil flows through cramped passage of valve, the rate of fluid speed increases and the oil pressure declines, thus cavitation occurring. In addition, this phenomenon appears when pump installed at a over height position, the oil absorption resistance is too large because the inner diameter of the suction pipe is too small, or when the oil absorption is insufficient because of pump speed is too high.
Air bubbles, which move through high pressure area with oil, break promptly due to the effort of high pressure, and then surrounding liquid particles compensate the bubbles at high speed, and thus the high-speed collision between these particles produces partial hydraulic impact. As a consequence, the pressure and temperature in part increases intensely, causing apparent shaking and noise.
At the surrounding thick wall where cavities congeal and the surface of elements, superficial metal particles fall off, due to long-term suffering from hydraulic impact and high temperature, as well as extremely corrosive effort caused by the gas from oil.
After illustrating the phenomenon of cavitation and its negative consequence, we are glad to share our knowledge and experience of how to forestall it from happening.
【1】Reduce the pressure drop at the place of flowing through small holes and interspaces: expected pressure ration of flowing before and after holes and interspaces is p1/p2 < 3.50 .
【2】Define diameter of hydraulic pump absorption pipe appropriately, and restrict fluid speed within pipe in many respects; decrease suction height of pump, and reduce the pressure damage to inlet line as much as possible.
【3】Choose high-quality airtightness T-junction and utilize high-pressure water pump as auxiliary pump to supply oil.
【4】Try to adopt all straight pipes in system, avoiding sharp turn and partially narrow slit.
【5】Improve element capability to resist gas etching.