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Technical Information
Adding or Changing Pump Fluid
The risk of explosion on large vacuum diffusion pumps is increased by
WARNING
these factors:
• Use of a hydrocarbon fluid as the pumping fluid. Hydrocarbon fluid is more prone
to explosion than synthetic silicone-based fluid. If a hydrocarbon fluid is being
used, check the entire system under vacuum before operating the pump.
• Low fluid levels in the pump which can lead to overheating. Low fluid levels
develop because the charge gradually depletes during use. The pump,
however, continues to operate normally and when the charge drops to 60% of
initial level, the boiler temperature may begin to rise. If this takes place, the
thermal switches open the heater circuits. For details, refer to "Overheating:
Detection by Thermal Switches".
• Overheated pump fluid that decomposes and becomes toxic. The toxic fluid
residue may be on the dipstick used to check fluid level, so care must always
be taken to assure personnel do not contact or ingest the fluid.
• Admission of atmospheric air during pump operation. Leakage of air into the
system allows oxygen into the fluid vapor and increases the risk of explosion.
If holding a vacuum is difficult, perform a leak test. Do not use the pump until
the leak source is located and repaired.
The recommended fluid charge for each pump is given in Table 4.
Fluids must be stored in clean, tightly closed containers and should be clearly
identified in accordance with their type. Do not mix pumping fluids of different types
and origins. Generally, it is not a good idea to mix used and new fluid for a pump
charge.
The use of Santovac® 5 Diffusion Pump Fluid is not recommended in these
CAUTION
pumps, nor is the use of any hydrocarbon fluid.
Information on Fluid and DP Performance
The choice of fluid depends on the application. The most common type of fluid
used in the market is a silicone based fluid, and all vacuum performance data in this
manual was generated using a silicone based fluid called DC704. There are many
fluids on the market that are equivalent to the DC704. The pump will operate with
other types of oil, but the performance may be different. Since there are so many
options, it is not possible to summarize and recommend them all.
54
High Throughput Diffusion Pumps User Manual
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