There are mainly 3 positions of seal structure for roots vacuum pump.
1. Motive Seal of the Driving Shaft Extension Parts (Seal between the Outside Atmosphere and the Gear Case)
At present, the motive seal of the driving shaft extension parts mostly adopts standard mechanical seals and skeleton vacuum rubber seals with reinforced rings. Mechanical seal ahs the advantages of small power consumption and higher line speeds, but is also has the disadvantages of complex structure and high cost. The skeleton seal has simple structure but large power consumption. In order to reduce the friction between the shaft and the seal ring, the shaft surface should ensure high hardness and finish. To prevent the wear of the shaft, a shaft sleeve with higher hardness that can be static sealed with the shaft can be installed to the shaft. In addition, a separate sealed box structure can also be used to make assembly and replacement of seals easier and more convenient. Also, the motor of some roots pump is sealed in the housing of one end of the pump body, thereby effectively solving the problem of dynamic sealing, increasing the vacuum degree and reducing the driving power. However, to prevent the arcing of the motor windings, the voltage of motor's power supply should be reduced below 50V. This structure is used for medium and small pumps.
Magnetic fluid seal is a kind of dynamic seal with long sealing effect and long service life. It has low power consumption but high cost.
2. Static Seal between Pump Body and End Cap or Gearbox
Since there are pre-suction pipelines in the gear box or the end cap housing connects with the outlet of the pump, the vacuum degree of these two parts is basically the same as that of the backing pump. Therefore, the pressure difference between the gear box and the pump chamber is small, and labyrinth seals, anti-spiral seals or piston expander seals are generally used.
3. Dynamic seal of the rotor shaft between the gearbox and the pump body (to prevent oil from entering the pump chamber and sealing between pre-vacuum and high vacuum)
The vacuum oil-resistant rubber ring seal is not only reliable but also easy to disassemble.
Polyurethane rubber gasket is used for plane sealing. It does not need to process sealing grooves and easy to disassemble.
The silicone room-temperature vulcanized rubber membrane seal is reliable, and it does not need the seal groove. But users must prepare the material, otherwise users cannot disassembled and repair the pump by themselves.