Vacuum Technology Know How - Triumf

Formula 2-7
Water vapor capacity
www.pfeiffer-vacuum.net
DIN 28426 describes the use of an indirect process to determine water vapor tolerance.
Water vapor tolerance increases at higher pump outlet temperature and greater gas ballast
volume q . It declines at higher ambient pressure.
pB
Without gas ballast, a vacuum pump having an outlet temperature of less than 100 °C would
not be capable of displacing even small amounts of pure water vapor. If water vapor is nevertheless
pumped without gas ballast, the condensate will dissolve in the pump oil. As a result,
the base pressure will rise and the condensate could cause corrosion damage.
Water vapor capacity
c w0 = p w0 . S
is the maximum volume of water that a vacuum pump can continuously intake and displace in
the form of water vapor under the ambient conditions of 20 °C and 1,013 mbar.
2.1.8 Sealing gas
When pumping corrosive process gas, there is a risk that the gas might attack parts of the
pump. To counter this danger, sensitive parts, e.g. bearings, must be protected by a continuous
flow of inert gas. A special gas inlet system is installed in the pumps for this purpose,
through which gas flows into the pumping system via the bearings. In this connection, it is
necessary to ensure that the base pressure does not increase excessively.
2.2 Rotary vane vacuum pump
6
5
Figure 2.2: Operating principle of a rotary vane pump
4
3
2
1
1) Housing
2) Rotor
3) Vane
4) Inlet / Outlet
5) Working chamber
6) Outlet valve
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