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Adding or Changing Pump Fluid
WARNINGS
The risk of explosion on large vacuum
diffusion pumps is increased by 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" on
page 25.
❑
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.
High Throughput Diffusion Pumps
37
The recommended fluid charge for each pump is given in
Table 4 on page 12.
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.
CAUTION
The use of Santovac
Fluid is not recommended in these
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 sum-
marize and recommend them all.
®
5 Diffusion Pump
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