A turbo-molecular pump has disadvantages like any vacuum pump. Here are some disadvantages:
(1) high cost
Turbo molecular pumps and cryogenic pumps at the pumping speed more than 1000l/s are expensive than the diffusion pump at the same pumping speed. However, due to the turbo molecular pump in the working process or other reasons, you can not use diffusion pumps and cryogenic pumps for special occasions though it is very easy to use. If compared with the small or medium diffusion pump, a small turbo molecular pump is relatively expensive. However, given the need for diffusion pump system valves, baffles, wells, valve controllers and pipes, the total cost is calculated, the difference between the two will not, in some cases, a turbo molecular pump or the expensive option .
(2) particulate matter or sediment sensitive
If an object (screws, pieces of glass, filament or silicon) fall into the turbo pump is in operation, the turbine will be damaged, often need to return to the manufacturer for repair. Once the damage is severe accident, there will be a few pieces of reuse. Rehabilitation, replacement parts are expensive. For safety reasons, the inlet of the pump mounted on the filter pores eye, in order to protect the normal operation of the pump. Such measures for the effective pumping speed of the pump losses. Deposited in thick sediments on the blades will cause wear on the blade and channel blockage, will also affect the rotor imbalance. If some of the particles into the bearing, causing wear, can reduce the working life of the pump. Therefore, in some applications, it is necessary to install a protective measure.
(3) Noise and Vibration
From experience, the pump will be vibration and noise problems, mostly bearing damage and poor balance arising problems. In normal operation, the pump is in a calm state, the maximum amplitude of 0.1 ~ 0.001μm (i.e. 100 ~ 1nm) between, been applied in some sophisticated equipment. The undetectable easily perceptible vibration as shown in Fig. For turbo pump(Barr Zeiss company’s 330 turbo molecular pump) spectral analysis. Vibration velocity V in units of μm / s, unit of frequency is Hz, the amplitude of the available calculation formula: d = V / 2πf, where d is the amplitude μm, f is the frequency Hz, the maximum amplitude of the resulting <0.005μm (<5nm) such a small vibration, turbo-molecular pump is running very smoothly, very little noise is also an issue for some special applications.
(4) the problem of broken
Some users fear of broken rotor blades do not dare to use the turbo molecular pump is broken during the normal operation of the pump impeller was suddenly inhaled foreign body or bearing wear and appear broken. Usually have protective measures, such as at the entrance to add filters, crushing is usually avoided.
(5) exposure to the atmosphere can lead to accidents
Any high vacuum during operation will encounter such incidents. Such as the regulation of rupture, the entrance of pipes, valves, seals problems, the vacuum pump inlet may suddenly exposed to atmospheric pressure. Different types of turbo molecular pumps, impact resistant ability atmospheric pressure is different. Some pumps due to resonance bending blades collide and damage, but some pumps by atmospheric impact without damage. The best way is by the manufacturers test result. Diffusion pumps and cryogenic pumps meet this sudden accident at work too much trouble, the resistance of the poor than the turbo-molecular pump, such as diffusion pump oil is oxidized rapidly contaminate the vacuum chamber, cryogenic pumps require regeneration.
To turbo molecular pump has a longer working life and the best operating performance, the user must use according to the rules and steps, these issues will be discussed in detail below.