Varian VHS-6, Instruction Manual

iv

Hazard

Suggested Corrective Action

Explosion

Integrate pressure relief valves in all systems using pumps 
10 inches or larger in diameter.
Do not use or recommend the use of hydrocarbon-based
pumping oils.

a. Explosion – Operation of the diffusion pump without prior and continuous evacuation (below 0.5

Torr (66.5 Pa)) or coolant and introducing a strong oxidizer (such as air) or explosive vapors or
powders or materials which may react with pumping fluids into a hot (above 300°F or 150°C) pump
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/or
shock waves.

b. All diffusion pumps are typically cleaned with acetone or alcohol. When combined with air, oxygen,

and other oxidizers, alcohol and most other solvents are very flammable and explosive. Never per-
mit 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.

Three elements are required: fuel, oxidizer, and source of ignition. A combination of temperature and
pressure can be a source of ignition. Most diffusion pump fluids except mercury are fuels. Hydrocarbon
oils are more prone to oxidize and explode than synthetic silicone-based oil. Oxidizers can be air (a
strong oxidizer) from a leak or can be deliberately introduced in a process or can be inadvertently
admitted to the system by operator or process controller error. Oxygen and other strong oxidizers are
even more dangerous. Certain conditions of temperature and pressure can cause a combustible mix-
ture to explode. The larger the diffusion pump, the greater the risk of explosion and the greater the risk
of damage and/or injury. Never operate diffusion pumps larger than 10 inches in diameter with hydro-
carbon oils without a full safety analysis for the complete system and application. Never operate any dif-
fusion pump in the following ways because they increase the probability of an explosion.

Prohibited Action

Explosion-Causing Condition

Run pump with no cooling water

Overtemperature

Run pump with low level of 

Overtemperature

pump fluid

Run pump without proper backing or

Overpressure

holding pump

Run pump when not evacuated below

Overpressure

0.5 Torr (66.5 Pa)

Admit air to, or rough through, 

Overpressure plus strong oxidizer

a pump with hot boiler