Vacuum pump is a kind of rotary variable volume vacuum pump, which can only be used with the cooperation of the front stage pump. It has a large pumping speed in a wide pressure range and is insensitive to dust and water vapor in the extracted gas. It is widely used in metallurgy, chemical industry, food, electronic coating and other industries. Vacuum pumps are widely classified, including water ring vacuum pump, rotary vane vacuum pump, roots vacuum pump, dry vacuum pump, piston vacuum pump, molecular vacuum pump, diffusion vacuum pump and so on.
Vacuum pumps are widely used in plastic machinery, pesticide chemical industry, dye chemical industry, brick and tile machinery, cryogenic equipment, papermaking machinery, pharmaceutical chemical industry, food machinery, industrial electric furnace, electronics industry, vacuum equipment, fertilizer, metallurgy, petroleum, mining, foundation treatment and other fields .
The function of vacuum pump is to extract gas molecules from the vacuum chamber, reduce the gas pressure in the vacuum chamber, and make it reach the required vacuum degree.
There are many vacuum pump manufacturers in China. Through the analysis of the global vacuum pump market, we can see that the market and application fields of various vacuum pumps are constantly changing and developing. Vacuum pump has a long history in China and abroad, and it has been widely recognized by domestic and foreign customers. Some vacuum pumps have been widely used in China and abroad.
Control problems of traditional vacuum pump
The load of vacuum pump decreases with the increase of vacuum degree. When the air resistance in the container is large, the vacuum pump often works in overload state. With the increase of vacuum degree, the current decreases and the motor works normally. When the container seal is normal, the motor working time under overload state is short, which will not cause the motor burning; when the container seal drops, the motor working time under overload state is prolonged, and the motor burning phenomenon occurs.
In order to solve the problem of pump overload, the following methods are traditionally used:
1) Mechanical automatic pressure regulating bypass valve is adopted.
The bypass valve is installed on the pontics pipeline between the outlet and inlet of Roots vacuum pump. This valve controls the pressure difference between the pump inlet and outlet not to exceed the rated value. When the pressure difference reaches the rated value, the valve will open automatically by the differential pressure, so that the outlet and inlet of Roots vacuum pump are connected, and the pressure difference between the inlet and outlet is reduced rapidly. At this time, roots vacuum pump works under almost no pressure difference load. When the pressure difference is lower than the rated value, the valve will close automatically, and the gas will be pumped from the front stage pump through roots vacuum pump. The roots vacuum pump with bypass relief valve can be started at the same time with the front stage pump, which makes the unit operation simple and convenient.
(2) Hydraulic coupling is adopted
The use of hydraulic coupling can also prevent the overload of the pump, so that the pump can work under high pressure difference. The hydraulic coupling is installed between the pump and the motor. Under normal working condition, the hydraulic coupling transmits rated torque from the motor end to the pump. The maximum pressure difference of Roots vacuum pump is determined by the maximum torque transmitted by the hydraulic coupling, and the maximum torque of the hydraulic coupling is adjusted by the amount of liquid in it. When the pump works under the high pressure difference or the front stage pump starts at the same time, there is a speed difference in the liquid coupling, that is, sliding, and only transmits a certain torque to slow down the pump. With the pumping process, the gas load decreases and roots vacuum pump gradually accelerates to the rated speed.
(3) Vacuum electrical components are used to control the pump inlet pressure
Pressure sensitive components such as vacuum capsule relay or electric contact vacuum pressure are installed at the inlet pipeline of Roots vacuum pump. After the vacuum system is started, when the pressure at the inlet of Roots vacuum is lower than the given value (allowable starting pressure of the pump), the pressure sensitive component will send a signal to start the roots vacuum pump through the electrical control system (if the bypass pipeline of Roots vacuum pump is installed in the vacuum system, the valve of bypass pipeline shall be closed at the same time). If the pump inlet pressure is higher than the specified value, the roots vacuum pump will be automatically closed (or the pump bypass pipeline valve will be opened at the same time); if the pump inlet pressure is higher than the specified value, the roots vacuum pump will be automatically closed (or the pump bypass pipeline valve will be opened at the same time), so as to ensure the reliable operation of Roots vacuum pump.
Obviously, the above methods have complex structure, high cost, poor control accuracy and serious energy waste, which can not meet the requirements of equipment development.
Application scheme of frequency converter
In order to protect the motor, some vacuum pump manufacturers use frequency converter, use current transformer and current transmitter to detect the actual current of the motor, and then input the converted analog signal into the frequency converter, and let the inverter do PID calculation, so as to control the motor current and motor speed, and finally achieve the purpose of protecting the motor.
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