- 12 -
[ Fig. 3]
9. Ultimate Pressure
"Ultimate Pressure" refers to the lowest attainable pressure of the pump.
Therefore, this pressure should be measured under the most favorable conditions.
It should be measured, using new pump oil, by means of a vacuum gauge installed
at the inlet of the pump; the rest of the vacuum system should be functionally
disconnected from the pump.
The measured values of the ultimate pressure of the rotary vacuum pump may
slightly a depending upon the kind of vacuum gauge used. According to the
"Japan Industrial Standard" [JIS] "ultimate pressure" is determined by means of a
McLeod gauge which is capable of measuring the partial pressure of air only.
If the ultimate pressure is measured without disconnecting the vacuum
equipment, the observed pressure may be higher than the specified ultimate
pressure of the pump due to the influence of the vapor or various kinds of gas
produced from water condensation or rust adhering to the inner wall of the
equipment. If any other gauge except McLeod gauge is used, the
above-mentioned difference may be very larger.
