The working fluid in the hydraulic system is flowing or temporarily stored in the capacity cavity of the hydraulic components (including piping). Circulation of the working fluid should be limited to the provisions of the cavity flow, but due to pressure, combined with the gap between the surface and other reasons, a small amount of liquid will cross the boundary of the cavity, flow to the other cavity should not go to the outside of the system, the liquid of this "out of the boundary" phenomenon known as leakage. The volume of liquid leaking out in a unit of time is called leakage, leakage is divided into internal leakage and external leakage of two kinds.
Internal leakage refers to a small amount of liquid within the hydraulic components from the high-pressure cavity leakage to the low-pressure cavity, such as liquid from the hydraulic pump high-pressure cavity to the low-pressure cavity of the leakage from the valve pressure channel to the return channel leakage.
External leakage refers to a small amount of liquid leakage to the outside of the hydraulic system, such as pipe joints, pressurized or non-pressurized fixed bonding surface of the static seal and axial sliding surfaces, rotating shafts outside the dynamic seal leakage. According to statistics, in the external leakage, piping leakage accounted for 44.5%; hydraulic cylinder leakage accounted for 21%; hydraulic pump leakage accounted for 9%; valves leakage accounted for 21.5 %; others accounted for 4%.
Leakage control is to improve the hydraulic transmission and electrical and mechanical transmission of the competitive ability of an important topic, it directly affects the expansion of the application of hydraulic technology, and thus get the world's hydraulic community attaches great importance to. It mainly includes two aspects: both to prevent the liquid leakage to the outside caused by environmental pollution, but also to prevent the external environment on the system. The development of leak-free components and systems will be one of the important directions of the world's hydraulic community's future efforts.
Leakage is an important issue that has long plagued the application, reputation and development of hydraulic technology, especially in the face of energy shortages, environmental pollution challenges faced by mankind today, leakage prevention and treatment of leakage is an urgent need to solve major technical problems. Summarized leakage can cause the following five hazards:
① make the system pressure instability.
② so that the speed of the actuator (speed) is not stable, the force (torque) is not normal, can not meet the requirements of the control, directly affecting the stability of the equipment, reliability and sophistication.
③ so that the hydraulic system efficiency is reduced, the oil (fluid) temperature increases, resulting in a vicious cycle of leakage.
④ may cause control failure, component damage, resulting in equipment failure, or even shutdown, increasing production costs.
⑤ cause the waste of oil (liquid) and other substances, pollute the environment and make people look at it, and may also cause fire, resulting in personal accidents.