hose who have used roots vacuum pump may know that most of them can't be started at atmospheric pressure (atmospheric pressure) except for a few roots vacuum pumps with direct air discharge. Let me explain why most roots vacuum pumps can't be started directly at atmospheric pressure.

Roots vacuum pump can include roots vacuum pump for low vacuum, mechanical booster pump and multi-stage Roots vacuum pump for medium and high vacuum. The roots vacuum pump with direct air discharge mainly includes wet roots vacuum pump and air-cooled Roots vacuum pump (multi-stage Roots vacuum pump can also discharge air directly). In order to realize the start-up under normal pressure, the vacuum degree is sacrificed in the structure of Roots vacuum pump. By increasing the rotor clearance, changing the structure of the rotor and strengthening the cooling, the operation of the multi-stage Roots vacuum pump is realized under the high-pressure difference (the multi-stage Roots pump realizes the high-pressure differential operation through the multi-stage rotors in series).

Why can't most roots vacuum pumps start directly under normal pressure

Structure principle of air cooled roots vacuum pump

In order to ensure the vacuum degree and pumping efficiency, we will not use the above changes. If forced to discharge the atmosphere directly, the pressure difference between the suction port and the exhaust port of Roots vacuum pump will be too large, which will overload the roots vacuum pump and make it unable to work. At this time, if the power of Roots vacuum pump motor is increased and the heat is increased, the rotor of Roots vacuum pump will overheat and cannot be dispersed, and the heat dissipation of shell will be faster, resulting in the formation of high temperature difference between them, so that the thermal expansion of Roots vacuum pump rotor will be accelerated, and the gap between them and the pump cavity will be lost, and then it will be stuck.

Therefore, in order to ensure that roots vacuum pump can achieve high vacuum degree, it is necessary to ensure the gap between roots vacuum pump rotor and pump cavity. Therefore, most of the medium and high vacuum roots vacuum pumps must be equipped with a front stage pump. The pressure in the system is pumped to a certain range by using the front stage pump, and then the roots vacuum pump is started to ensure the inlet and outlet pressure difference within a reasonable range. In this way, the overload of Roots vacuum pump caused by high pressure difference can be avoided.

Before roots vacuum pump, water ring vacuum pump, oil seal vacuum pump and reciprocating vacuum pump can be used to directly discharge the atmosphere. After the appearance of screw oil-free vacuum pump manufacturer's screw oil-free vacuum pump, it can be combined with roots vacuum pump to form a clean oil-free vacuum system with wide range and large pumping speed, so as to realize the clean vacuum environment difficult to be realized by traditional pumps.