Vacuum diffusion pump operating procedures
1. Check all parts of the vacuum system, familiarize yourself with the gas path structure of the system, understand the functions of the various components of the vacuum system, and the circuit connections of the operating parts.
2. Close the deflation valve, start the mechanical pump, pump the system, and use the spark leak detector to check all parts of the system. In the case of an all-metal system, the valve can be closed and the P-t curve recorded as a vacuum gauge reading (for a static boost test). If the pressure rises linearly with time, it can be concluded that the system has a leak source and should be leak tested.
3. When the system vacuum reaches the pre-pressure of the oil diffusion pump (5×10-2 Torr), start the diffusion pump to gradually increase the heating current to the rated value. Cool water should be turned on before starting the diffusion pump.
4. After the diffusion pump is working normally, use a spark leak detector (or thermocouple meter) to judge the vacuum of the measurement system. An ionization gauge can be used up to 10-3 Torr (a thermocouple is nearly full or 95 squares or more). When using, first degas the regulation, then measure the degree of vacuum.
5. Bake and degas the system. For the glass system, the hard glass baking temperature is 400 ° C ~ 450 ° C, and the soft glass is 350 ° C ~ 400 ° C. Degassing time depends on specific requirements, usually 1 to 2 hours. After the degassing, the vacuum is still not up to the requirement, and the P-t curve should be recorded using the ionization meter to determine whether it is leaking. You can also use the acetone, alcohol, etc. to smear the suspicious place, see the swing of the hands to find the leak. If it is bad for degassing, it should be further baked and degased for a long time. The new system generally takes a long time to reach the desired vacuum. If the vacuum is too old, consider whether the system design, installation is reasonable, whether there is dead space, whether the gas source is more or not, whether the dirt is brought in during maintenance, whether the container is cleaned, and other factors.