The structure of vacuum pump main engine (also known as machine head) is usually composed of a pair of meshing gears (screw, main engine housing, high pressure end and end cover, low pressure end and end cover).

When the main engine of screw vacuum pump runs normally, there is no contact between screw and screw, between screw and main body shell and between high and low pressure end face (there is a small gap filled by screw vacuum pump oil).

The technical performance of screw vacuum pump head is mainly guaranteed by the following three aspects:

1. High precision machining

The processing of screw, main engine shell and high and low pressure end is high precision. The accuracy ensures that there are proper gaps between the screw and the screw and between the screw and the shell of the main engine after assembly. The size of the clearance has fully considered the deformation of the screw and the shell when the main engine runs at high temperature.

2. Gap

The clearance between the screw and the high and low pressure end face is ensured during screw assembly according to the technical requirements.

When the main engine is running, there is no axial movement of the screw, and the allowable radial displacement of the screw is guaranteed by the high-precision bearing.

3. Lubricating oil

The oil film formed by the lubricating oil during the normal operation of the machine head prevents the screw from contacting with each other directly.

However, with the running time of the screw vacuum pump, the bearings of the main engine will inevitably wear, resulting in the axial movement of the screw and the increase of the radial displacement, which will change the clearance between the screw and the screw, between the screw and the shell of the main engine and between the front and rear end faces.

These clearance changes are normal and allowed within the life span of the bearing, and the attenuation of the gas production of the screw vacuum pump and the increase of the load of the main motor are also normal and permissible. With the operation time of the unit approaching the overhaul period of the machine head, the service life of the main engine bearing gradually tends to the maximum allowable time limit.

At this time, the axial and radial displacement of the screw gradually tends to the maximum design allowable value, which will make the gap between the screw and the screw, between the screw and the shell of the main engine and between the front and rear end faces.

At this time, although the main engine of screw vacuum pump is still safe, it is time to consider the plan and arrange the overhaul of the main engine.

Once the operation time of the unit exceeds the overhaul period, the bearing wear and the matching clearance of the main engine will reach the limit value allowed by the technical conditions of the main engine. At this time, the main engine will be in unsafe operation state, and the following serious consequences may occur at any time.

The operation load of vacuum pump head increases, which is harmful to the main motor and electrical system. The possible strong friction between the screw in the head of screw vacuum pump, between the screw and the front and rear end faces, and between the screw and the housing of the main engine, will make the operating load of the main engine increase rapidly. In addition, the operating load of the bearing with serious wear is also very large.

In this way, the motor will be in overload state, which will seriously endanger the safe operation of the motor. If the situation is serious, if the electrical protection device of vacuum pump unit is not sensitive or fails to respond, it may also lead to motor burnout.

Normal overhaul of main engine is not only the basic requirement of equipment maintenance, but also the basic requirement of enterprise to control normal equipment maintenance cost, avoid unnecessary capital loss and ensure normal production of enterprise. It is not only reasonable but also necessary to remind users to carry out regular overhaul according to the instructions of vacuum pump on time.

Screw vacuum pump is easy to meet the faults in the work, such as no reaction after connecting the power supply, difficult to start or unable to start, accompanied by "buzzing" sound, the motor can run, but the speed is slow, and the casing is overheated, there is burning smell, noise and vibration during operation.