Ulvac GLD-137CC, Инструкция по эксплуатации

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5. Pump Performance
5.1 Ultimate pressure
The term “ultimate pressure” as employed in the catalogue and in this manual is defined as “the
minimum pressure obtained by the pump without the introduction of gas from the pump inlet
(i.e. the non-load condition).” For this pump, measurement is performed using the specified
pump oil with only a Pirani vacuum gauge installed at the pump inlet port.
Note that the Pirani gauge shows values approximately five to ten times higher than those
shown by the McLeod gauge. This is because condensable gas components (mainly moisture)
included in the measured air are removed when the McLeod gauge is used.
Also, the actual ultimate pressure of the vacuum device becomes higher than that noted in the
catalogue for the following reasons.
➀
The vacuum gauge is installed at a distance from the pump, and the steam and a variety of
gases are generated by water droplets and rust on the inside walls of the pump and piping.
➁
Gasifying of volatile components which have dissolved in the pump oil. (Deterioration of
pump oil)
➂
Existence of a gas supply source including vacuum leakage in the vacuum path.
5.2 Pumping speed
The pumping speed of the pump depends on the type and pressure of the gas to be evacuated.
The pumping speed usually reaches the maximum at a high pressure range, and it gradually
decreases as the pressure reduces.
The nominal pumping speed of this pump is the maximum pumping speed when dry air is
evacuated. Fig. 10 shows the relationship between the evacuation pressure and pumping speed.
5.3 Power requirement
The power required to operate the pump is the total of the power required to overcome the
rotational resistance of the pump (mechanical work) and the power required to compress the air
(compression work), and reaches a maximum at an inlet evacuation pressure of around 2.7
×
10
4
to 4
×
10
4
Pa. If the inlet evacuation pressure has reduced to 13.3 Pa or less, the compression
work is considerably reduced and more power is consumed in mechanical work.