Selection of Oils for Mechanical Rough Pumps
Whenever selecting mechanical pump fluids for use in Mass Spectrometers,
it is important to select the fluid with the lowest vapor pressure.
The vapor pressure of the oil is important because it determines
the ultimate vacuum the pump can achieve. Lower vapor pressures
will allow the user to minimize backstreaming, significantly reduce
pumpdown time and maximize vacuum. The major three mineral based
oils used for rough pumps in mass spectrometers include Inland
19, Invoil 20 and Inland 45. Any of these pump fluids can be used
in all Edward, Alcatel, Welch and other mechanical rough pumps.
|
Comparison of Rough Pump Oils |
| |
Inland 19 |
Invoil 20 |
Inland 45 |
Inland TW |
Fomplin Y06/6 |
| Vapor Pressure |
3 x 10-5 torr |
3 x 10-6 |
1 x 10-7 |
1 x 10-6 |
3 x 10-6
|
The selection of a specific grade of pump oil utilized depends
on the users needs including the mass range of the mass spectrometer,
the system cleanliness required, the sensitivity required and
the cost the user is willing to pay.
-
Inland 19 is the basic mineral oil used in most mass spectrometer
vacuum pumps. It has been engineered for use with all mechanical
vacuum pumps, providing for minimal backstreaming.
-
Invoil 20 is a better grade of mineral oil for use in mechanical
rough pumps. It has been distilled to remove the majority of the
light fractions present in the base oil. These light fractions
represent weak links in oil and tend to provide a source of attack
for reactive gases. In addition they can easily migrate into the
vacuum system to increase mass spec background. Invoil 20 will
provide for better pumping efficiency, lower vacuum and longer
vacuum pump life in comparison to Inland 19 or similar oils.
-
Inland 45 is the newest and best grade of oil for mechanical vacuum
pumps for mass spectrometers. It is a highly refined and distilled
pump oil which will provide for optimum vacuum levels and minimal
mass spectrometer background. It is recommended for mass spectrometers
such as high resolution instruments which require the cleanest
system, highest vacuum levels and optimum pumping efficiency.
This oil is now recommended for the H.P. mass spectrometer systems.
-
Inland TW mechanical pump fluid is specifically recommended for
applications where exposure to reactive or corrosive gases is
prevalent, such as electrospray and particle beam.
-
Fomblin PFPE oils are non-flammable chemically inert fluids for
use in areas where there are high levels of oxygen or where serious
corrosion is a problem. This oil is identical to Krytox. Several
manufacturers recommend this pump fluid for uses such as in the
H.P. Particle Beam mass spectrometer.
See also Inland vacuum fluid shelf life.
See individual mechanical pump oil pages for part numbers and
prices
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