Instruction manual

3
High Throughput Diffusion Pumps
DRAFT 12/23/04
Pressurization Hazards
❑ Large vacuum pumps and their components are
designed for vacuum service; they are not designed
to be pressurized which could cause them to burst
possibly expelling shrapnel at lethal velocities.
Serious accidents have been caused by intentional
pressurization of vacuum systems and their compo-
nents.
❑ Never pressurize any part of a vacuum system for
test or any other purpose.
❑ Always provide pressure relief when designing
diffusion pumps into systems and ensure that
pressure relief motion is limited to safe
envelopes.
❑ Never permit the hazards in Table 3 to develop.
❑ Pressure Relief Devices: Systems must be designed
with pressure relief devices to provide safe pressure
relief from internal explosions. Always recognize that
safety devices can fail or malfunction; provide redun-
dant protection by installing devices having different
failure modes, failure mechanisms, and failure
causes. Be certain that exhaust duct materials are
capable of withstanding the corrosivity, temperature,
and pressure of exhausted products.
Dangerous Substances
❑ Chemical Dangers of Acetone and Alcohol: Diffusion
pumps are typically cleaned with acetone or alcohol.
Acetone, alcohol, and most other solvents are irri-
tants, narcotics, and depressants, and/or carcino-
genic. Their inhalation and ingestion may produce
serious effects. Even absorption through the skin can
result in moderate toxicity. Always ensure that clean-
ing operations are performed in large, well-ventilated
rooms. Use of self-contained breathing apparatus
may be necessary depending upon the solvent type
and vapor concentration in surrounding air.
❑ Poisonous and Corrosive Compounds: When pump-
ing poisonous, reactive, and/or corrosive gas, vapors,
or chemicals, proper operation and regeneration do
not always ensure that all hazardous materials have
been totally removed. If hazardous gas, vapors,
chemicals, or combustible mixtures are pumped, suf-
ficient quantities may exist during operation or
remain after regeneration to cause severe injury or
death.
❑ Pump Fluids: Overheating the pump fluid, exposing it
to air or reactive materials, or overpressurizing it
above the normal operating range, approximately
1x10
−
3
Torr (1.3x10
−
3
mbar) decomposes the fluid
and possibly makes it toxic. This is especially true of
backstreamed mechanical pump fluids which are
more volatile (unstable). Overheating of accidentally
introduced or backstreamed mechanical pump fluids
cannot be protected against by thermal switches
which are set for diffusion pump fluid.
❑ Process Gasses: Process gasses are frequently toxic,
flammable, corrosive, explosive, or otherwise reac-
tive. Vacuum Technologies has no control over the
types of gasses passing through the user’s diffusion
pump as these are entirely under the control of the
process user and/or the hardware systems integrator.
Since these gasses can cause serious injury or death,
it is very important to plumb the exhaust of the pump
to the facility’s hazardous gas exhaust system which
incorporates appropriate filters, scrubbers and similar
components to ensure that the exhaust meets all air
and water pollution control regulations.
Table 3 Pressurization Hazards
Prohibited Action Result
Do not block inlet or
vent of liquid nitrogen
trap and lines
LN
2
trap and/or
lines burst
Do not close isolation
valves at inlet and
discharge of main
water cooling coils
when pump is heated
Water turns to steam
and bursts coils
Do not pressurize
the pump body
(above 1 atm.)
Body of pump bursts
Do not make a hole
through the vacuum
wall
Loss of structural
integrity of wall