Isobaric characteristics of hydro-pneumatic maintenance : Pascal's law "equilibrium fluid pressure at a certain point in a liquid is transmitted to all parts of the liquid equally"
Equal volume characteristics: Assume that the volume of liquid given out by hydraulic cylinder 1 is equal to the volume absorbed by hydraulic cylinder 2.
Hydraulic transmission can transmit force: the force ratio is equal to the ratio of the two piston areas
Hydraulic transmission speed: the speed ratio is equal to the inverse ratio of the two piston areas v2 / v1 = A1 / A2 can be written as: A1v1 = A2v2 = Q (flow)
This is called the principle of fluid flow continuity in fluid mechanics, and it reflects the reality of mass conservation in physics. F1v1 = F2v2 = N = pQ (power) indicates energy conservation.
In summary, the basic characteristics of hydraulic transmission can be summarized as follows:
The liquid is used as the transmission medium. The static pressure of the liquid in the closed container is used to transmit power. The static pressure depends on the external load. The transmission of the load speed is based on the principle of equal volume change of the liquid. The speed depends on the flow rate. .
Therefore, the use of hydraulic transmission can achieve the purpose of transmitting power, increasing power, changing the speed ratio, etc., and keeping the power unchanged without considering the loss.
Advantages of hydraulic transmission:
(1) Small size, light weight, small inertia, fast response speed
(2) Achieve stepless speed regulation with a wide range of speed regulation
(3) Can alleviate impact and smooth movement
(4) Easy to implement overload protection
(5) The hydraulic components have a self-lubricating effect and have a long service life.
(6) Easy to implement automatic control
Disadvantages of hydraulic transmission:
(1) Leakage problem (can be overcome through process)
(2) The control is more complicated: there are many nonlinear factors and it is difficult to accurately model
(3) After two conversions of energy, the efficiency is lower than the other two transmission methods
(4) The manufacturing and maintenance requirements of hydraulic components are high
The viscosity of hydraulic oil is measured by viscosity. It is divided into three types: dynamic viscosity, kinematic viscosity, and relative viscosity. The viscosity of a liquid increases with increasing pressure, but the value at is not large. Therefore, it is generally ignored in the use of general hydraulic systems. But the viscosity has a great influence with the temperature, and the viscosity will decrease as the temperature rises. This relationship is called the viscosity-temperature characteristic of hydraulic oil, and this characteristic determines the use of hydraulic oil. In the working temperature range, the flash point and ignition point must be high to meet the fire protection requirements. The freezing point and flow point should be low to ensure that the oil works properly at lower temperatures. It is non-corrosive and has good compatibility.
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