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Vacuum System
5
Turbomolecular pump and fan
Turbomolecular pump and fan
The 250 liters/second turbomolecular (turbo) pump creates the low pressure
(high vacuum) required for correct analyzer operation. The turbo pump in the
MSD is clamped directly to the bottom of the vacuum manifold.
The turbo pump has a cylindrical body with its inlet open to the interior of the vac-
uum manifold. Inside the pump body is a central shaft or cylinder. Sets of small
blades (airfoils) radiate from the central shaft, which spins at up to 60,000 revolu-
tions per minute.
The turbo pump transports gas by momentum transfer. The turbine blades are
angled so that when they strike a gas molecule it is deflected downward. Each set
of blades pushes the gas molecules further down toward the pump outlet. The
foreline pump is connected by a hose to the outlet of the turbo pump. It removes
the gas molecules that reach the outlet.
A separate controller regulates current to the pump and monitors pump motor
speed and temperature. A cooling fan is located between the turbo pump and the
front panel of the MSD. The fan draws air from outside the MSD and blows it over
the pump.
The turbo pump turns on automatically as soon as the MSD power is switched on.
The system will allow the analyzer to be turned on when the turbo pump is greater
than 80% speed, but the pump normally operates at 100% speed. The turbo pump
-5
Torr for GC carrier gas
typically maintains an indicated pressure below 7 x 10
flows up to 4 ml/minute. Pressure (vacuum) can only be measured if your MSD is
equipped with the optional gauge controller.
The turbo pump spins up (starts) and spins down (stops) quickly. This simplifies
pumpdown and venting. From initial power-on, the system can pump down to
operating pressure in 5 to 10 minutes.
The MSD ChemStation has pumpdown and venting programs to guide you through
these procedures. Follow their instructions carefully.
See Also
Gauge controller, page 208
To pump down the MSD, page 58
To vent the MSD, page 52
Table 2. Typical MSD pressure readings for various carrier gas flow rates,
page 45
202
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