Varian NHS-35, Инструкция по эксплуатации, Страница: 34 / 49

Installation
1-14
a Confirm the vacuum ultimate pressure characteristics of the mechanical pump. This should
closely approximate the value quoted in the manufacturer’s data, if the mechanical pump is
correctly installed, adjusted, and filled with clean oil. Pressure measurements should be made
with a continuously indicating total pressure gauge, such as a thermocouple gauge. This test
can be performed to evaluate either valved or unvalved systems. Connect the outlet or foreline
of the diffusion pump to the inlet of the mechanical backing pump, using appropriate vacuum-
tight connections.
b In the case of a valved system, close the roughing valve and main isolation valve ahead of
the diffusion pump. In the case of unvalved systems, the entire work chamber volume must
be included in the test. Evacuate the entire system with the mechanical pump only. Let the
mechanical pump reach an ultimate pressure in the system. This reading should approximate
the value obtained in step a above (usually 10 to 50 microns (1.33 to 6.65 Pa)). If it does not,
examine for leakage. If leakage is suspected, follow standard procedures for leak testing.
These will depend on the type of vacuum gauges and/or leak detection equipment available.
The most effective are Varian’s helium leak detectors.
1-7 ADDING PUMP FLUID
a. The recommended fluid charge for the pump is three gallons. The fluid charge will gradually
be depleted through use, but the pump will continue to operate normally. When the charge is
reduced to approximately 60% of the initial amount, the boiler temperature may begin to rise
and under this condition the thermal switch is designed to open the heater circuit.
b. This diffusion pump is furnished with fill and drain fittings with special Viton elastomer
sealed plugs.
WARNING
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The risk of explosion in large pumps is increased by hydrocarbon oils,
low fuel levels, or opening either fill or drain plugs during operation.
Never operate diffusion pumps larger than 6 inches with hydrocarbon
oils without a complete safety analysis for the specific system and appli-
cation. Hydrocarbon oils are more prone to explode than synthetic sili-
cone-based oils, similarly the larger the diffusion pump the greater the
risk of explosion. Running the pump with low oil level causes hot sur-
faces and the oil to be decomposed and very toxic. Such decomposed
oil and any residue from toxic/corrosive materials pumped will be pre-
sent on the dipstick when the fluid level is measured.
NOTE
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Fluids must be stored in clean, tightly closed containers and should be
clearly identified in accordance with their type. Do not mix pumping flu-
ids of different types and origins. Generally, it is not a good idea to mix
used and new fluid for a pump charge.