Vacuum pump unit is usually composed of the following parts: various vacuum pumps; vacuum measuring unit; vacuum valve; vacuum pipe and some other components, such as blower, vacuum connector, air tank, bellows, dust collector and vacuum relay.
According to the working pressure of the unit, there are crude vacuum pump unit (> 1330pa), low vacuum pump unit (1330 ~ 0.13pa), high vacuum pump unit (0.13 ~ 1.3 × 10-6 PA), ultra-high vacuum pump unit (1.3 × 10-6) ~ 1.3 × 10-11 PA and very high vacuum pump unit (< 1.2 × 10-11 PA).
Roots vacuum pump (supercharger pump) for high vacuum can not be directly discharged into the atmosphere. For example, the direct exhaust atmosphere will cause the pressure difference between the inlet and the exhaust port of the roots vacuum pump to be too large, thus overloading the roots vacuum pump. Increasing the power of the roots vacuum pump motor will cause the roots vacuum pump to overheat, so the small gap between the roots vacuum pump rotors will be stuck rapidly due to thermal expansion. In order to ensure that the roots vacuum pump can achieve a higher degree of vacuum, it is necessary to ensure the gap between the rotors of Roots vacuum pump. Therefore, the roots vacuum pump must be equipped with a front-end pump. When the pressure in the system is pumped to a certain range through the front-end pump, the roots vacuum pump is started, which can prevent the roots vacuum pump from overloading. The front stage pump can be a vacuum pump which can be directly discharged into the atmosphere, such as water (liquid) ring vacuum pump, rotary vane vacuum pump, slide valve vacuum pump or reciprocating vacuum pump.
Under normal conditions, roots vacuum pump unit has more advantages than other vacuum pumps in using water ring pump as the front stage pump, mainly because it can remove a large number of condensable steam, especially when the mechanical vacuum pump in the gas town eliminates condensation. There is insufficient steam capacity, or the solvent used will degrade the pump oil and affect the performance, or it is more obvious when the vacuum system does not allow oil pollution.
The main characteristics of low vacuum pump unit are high working pressure and large displacement, but the pumping speed is lower than that of high vacuum pump unit. It is widely used in vacuum pumping and vacuum cleaning, vacuum impregnation, vacuum cleaning, vacuum degassing, vacuum drying and other equipment. The main pump of low vacuum pump unit is commonly used reciprocating vacuum pump, oil seal vacuum pump, water jet pump, water steam jet pump, water ring pump, oil steam jet pump, molecular sieve adsorption pump and roots pump. When using the low vacuum pump unit, the components such as dust collector and dry filter must also be configured according to the process requirements of cleanness and humidity of the pumped gas.
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