Pump Performance; Ultimate Pressure; Pumping Speed - Ulvac PMB-040C Instruction Manual

YK10-0015-DI-002-03

2.4 Pump Performance

2.4.1 Ultimate pressure

The ultimate pressure of the mechanical booster pump depends on that of the backing pump.
Take special care when using the backing pump other than the standard combination. In the event
of an abnormal ultimate pressure, it is also necessary to check the ultimate pressure of the backing
pump alone.
In addition, for pumps that exhaust a large amount of moisture or that have been left with the intake
and exhaust ports open in the atmosphere for a long period of time, their ultimate pressure may not
drop to the specified value immediately after the startup due to moisture adhering inside the pump.
In many cases, they recover their normal conditions after the no-load running for a whole day and
night under that condition as the adsorbed substances are evaporated again.

2.4.2 Pumping speed

The pumping speed of the mechanical booster pump changes depending on the inlet pressure.
Also, the pumping speed of the mechanical booster pump fluctuates depending on the difference of
the inlet port/the outlet port pressure of the mechanical booster pump during operating.
An increase of pumping speed of the backing pump allows the inlet port/the outlet port pressure
difference to lessen.
As a result, the pumping speed of the area on the atmospheric pressure side becomes larger due to
the pressure which the maximum speed of the mechanical booster pump comes out. Reversely,
upon the pumping speed of the backing pump being small, the pumping speed of the mechanical
booster pump becomes small.
When the mechanical booster pump is used in combination with a backing pump other than the
standard one (rotary pump or water sealing pump), it is necessary to examine its pumping
performance to see if the required pumping speed and ultimate pressure can be obtained.
Fig. 7 Pumping speed curves
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