Agilent Technologies VHS-4, Instruction Manual

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VHS-4 Diffusion Pump
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DRAFT 8/7/02
Explosion
❑ Operation of the diffusion pump without continuous
evacuation below 0.5 Torr (0.67 mbar), or without
coolant and introducing a strong oxidizer (such as
air) or explosive vapors or powders or materials
which may react with pumping fluids in a hot pump
(above 300 °F or 150 °C) can cause an explosion.
Such an explosion can violently expel valves and
other hardware, slam open doors that are not
designed for appropriate pressure relief, or burst other
components of the vacuum system. Serious injury or
death may result from expelled parts, doors, shrapnel,
and shock waves.
❑ Three elements are required for explosion: fuel, oxi-
dizer, and an ignition. A combination of temperature
and pressure can be a source of ignition. Most diffu-
sion pump fluids, except mercury, are fuels. Hydro-
carbon oils are more prone to oxidize and explode
than synthetic silicone-based oil. The oxidizer can be
air, which is a strong oxidizer that is introduced by a
leak, deliberately brought in via a process, or inad-
vertently admitted by operator or by a process con-
troller error.
❑ Explosion and Fire from Acetone and Alcohol: Diffu-
sion pumps are typically cleaned with acetone and
alcohol. When combined with air, oxygen, and other
oxides, alcohol and most other solvents are very
flammable and explosive. Never permit any trace of
these cleaners to remain in or on the pump. Always
remove all traces of alcohol and acetone and other
cleaners with clean, dry, oil-free compressed air.
Oxygen and other strong oxidizers are even more
dangerous than air. Certain conditions of temperature
and pressure can cause a combustible mixture to
explode. The larger the diffusion pump, the greater
the risk of explosion and the greater the risk of dam-
age and injury. Never operate large diffusion pumps
utilizing hydrocarbon oils without a complete safety
analysis for the entire system and for the application.
Never operate a large diffusion pump under the condi-
tions listed in Table 2. Any of these situations increases
the probability of an explosion.
Table 2 Explosive Conditions
Prohibited Action Explosion-Causing Condition
Do not run pump without
cooling water Overtemperature
Do not run pump with low
level of pump fluid Overtemperature
Do not run pump without
proper backing or holding
pump Overpressure
Do not run pump when
not evacuated below
0.5 Torr (0.38 mbar) Overpressure
Do not admit air to, or
rough through, a pump
with hot boiler Overpressure plus strong
oxidizer
Do not open drain or fill
plug while pump is under
vacuum, especially when
it is hot Overpressure plus strong
oxidizer
Do not contaminate pump
with explosive vapors Lower explosive threshold
of gas mixtures
Do not remove, defeat, or
override safety
counter-measures such as
pressure and thermal
switches and valve
sequencer interlocks Overtemperature,
overpressure, more
combustible mixtures
Do not machine or weld
any part of the pump
without removing all oil or
solvent residue in pump in
large pumps Source of ignition
Do not use unsuitable
pumping fluid, especially
hydrocarbon oil Lower explosive threshold
of gas mixture