The sealing device of roots vacuum pump

Roots vacuum pump seal should mainly consider three parts: the first is the shaft overhang of spindle nose through the dynamic seal of pump cover, shaft protective outer surface seal), the other is gear box cover and the static seal between the end cover and the cover and pump body, a third is the shaft drive shaft head overhang pump cover sealing in the case. Different measures should be taken for the sealing conditions of the three parts, which are discussed below.

The extension part of the shaft head passes through the dynamic seal at the pump cover: the seal here is very important. If the seal is not strict and leakage occurs, the suction performance of the vacuum pump will be seriously affected. Special attention must therefore be paid. There are many kinds of sealing measures adopted at present, the most common are mechanical seal, asbestos disc root seal, leather bowl seal and anti-screw seal.

(1) mechanical seal Its structure, USES morer is double friction ring type mechanical seal, mechanical seal and reliable operation, small power consumption, allows the linear velocity is large, but the structure is complex, the manufacturing cost is high.

(2) the leather bowl seal with reinforcing ring consumes a little more power, but it is simple in structure and easy to replace, and usually comes with spare parts in the factory. Cup with vacuum pump oil or MoS2 dry oil lubrication, cup materials eyes using butyl rubber, its linear velocity permitted under 12 m/s, the temperature is below 120 ℃, fluorine rubber, linear velocity can reach 30 m/s, the temperature can reach 250 ℃.

(3) the asbestos packing seal The sealing structure is simple, low cost, change is easy, but you need cooling lubrication, or generated by the friction heat loss of high temperature will make the axis, in order not to damage shaft, shaft should be set up at the case. In order to reduce friction, the surface hardness and finish of shaft sleeve are very high. The surface of shaft sleeve is often hardened or carburized and then polished.

(4) the transmission shaft of the roz vacuum pump with reverse screw seal structure can also be sealed with reverse screw through the seal at the pump cover. Reverse screw seal is the use of a threaded sleeve on the outer diameter of the shaft on the shaft, and along with the shaft rotation, like a screw pump, play a sealing role.
Against referred to as the helical seal screw seal and spiral seal depend on axial force of round nut and fixed on the shaft, with the axis of rotation, and retains certain radial clearance between the end cover, general gap of 0.10 ~ 0.25 mm, when the axis of rotation, screw seal like screw pump oil is pushed him back.

After use, the reverse screw seal has the following characteristics:

1) ensure the lubrication of the bearing. When the shaft rotates, the screw seal works like a screw and sends oil to the bearing continuously to ensure the lubrication of the bearing;

2) free from the limitation of pump shaft speed, the higher the speed, the greater the sealing pressure, especially when the speed is high, the sealing effect can be played to ensure that there is no oil in the pump;

3) screw seal with shaft rotate at the same time, and have certain radial clearance between the stationary, no friction loss, reduce the power consumption, and produce less heat, long life, don’t cause vibration and noise, high reliability;

4) low precision requirement and easy production;

5) the materials are generally cast iron, so the cost is low;

6) this sealing structure can only show its sealing effect when the shaft reaches a certain speed, and it will not work at all at rest. Therefore, this method is not suitable for places where sealing is required in static state. But no adverse effects on the roots vacuum pump, mainly because of the roots vacuum pump after stalling, the pump cavity and static seal between front and back cover not required, but only to run when the pump is containment requirements. Especially the rotz vacuum pump with high speed operation, the dynamic sealing performance is very good.