YK08-0028-DI-002-08
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5. Pump Performance
5.1 Ultimate Pressure
“Ultimate pressure” described in the catalogue and this document means “the limit value pressure
obtained by the pump in a state not introducing any gas through the suction inlet (no load
operation).”
ULVAC measures the value by the Pirani gauge connected to the Pump suction inlet using the
specified vacuum pump oil after having completely blocked out the Pump unit from the system.
Be cautious as the Pirani gauge as well as the thermocouple vacuum gauge would indicate a
value 5 to 10 times much than the value that the Mcleod gauge shall indicate. This is caused by
the fact that the Mcleod gauge shall get rid of the condensed gas constituent (mainly water)
included in the measured gas.
Actual vacuum equipment on the site shall likely to raise the ultimate value higher than the
catalogue value as the vacuum gauge was put far away from the Pump or maybe affected by the
water drop, rust or other substances attached to the system inside wall or pipe, or water vapor
and miscellaneous gas generated from attached substances. It is because the oil vapor pressure
is raised up since the volatile gas melt in the Pump oil, foreign substance and gas sucked in the
Pump from the vacuum chamber might contaminate the gauge head and/or decompose
(deteriorate) the Pump oil constituent.
5.2 Exhaust Speed
Exhaust speed of the Oil rotary pump shall vary depending on the type and pressure of the
sucked gas. It shall indicate the maximum exhaust speed in the high pressure range and lower
speed little by little lower becomes the pressure.
Effective exhaust speed of this machine is the maximum value when it sucked in the dried air.
Fig. 10 show the relation of the suction pressure and exhaust speed.
