Ultra-high vacuum diffusion pump oil must be used in strict accordance with operating specifications to ensure vacuum system performance, extend oil life, and avoid contamination. Specific precautions are as follows:
1. System Pretreatment and Cleaning
Before changing the oil, thoroughly clean the interior of the diffusion pump to remove any remaining old oil, carbonized matter, and impurities. Flushing with a dedicated solvent (such as trichloroethylene) can prevent mixing of new and old oil, which could degrade performance.
Ensure that system piping, valves, and other components are free of rust, oil stains, or particles to prevent contaminants from entering the oil and affecting vacuum levels.
2. Filling and Level Control
When filling, operate in a clean environment to avoid dust and moisture. Using a dedicated filter funnel is recommended.
The oil level must be strictly controlled between the "minimum" and "maximum" markings on the pump body. A low oil level can lead to unstable vapor flow and reduced pumping speed; a high oil level can cause boiling oil to splash and contaminate the system. 3. Heating and Startup Specifications
The system must be pre-evacuated to a low vacuum (typically ≤1 Pa) using a foreline vacuum pump before starting the diffusion pump to heat the system. This prevents the oil from boiling violently at low pressure and causing decomposition.
The heating power must match the oil's characteristics to avoid overheating. (For example, methylphenyl silicone oil typically withstands temperatures between 200°C and 300°C; overheating can cause cracking and increase vapor pressure.)