Agilent Technologies 5975T LTM GC/MSD, Troubleshooting And Maintenance Manual

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Vacuum System
12
Troubleshooting and Maintenance Guide 193
Vacuum Seals
Vacuum seals are shown in Figure 27 .
Several types of Viton elastomer O-ring seals are used to
prevent air leaks into the analyzer chamber. All these O-rings,
and the surfaces to which they seal, must be kept clean and
protected from nicks and scratches. A single hair, piece of lint,
or scratch can produce a serious vacuum leak. Two of the
O-rings are
lightly lubricated with Apiezon-L vacuum grease:
the side plate O-ring and the vent valve O-ring.
Face seals
A face seal is an O-ring that fits in a shallow groove. The sealing
surface is usually a flat plate. The manifold side plate and end
plate O-rings fit into grooves around the large openings in the
analyzer chamber. The side plate swings into place against the
side plate O-ring, and must be held in place when the MSD is
turned on for pump down to assure a good seal.
The front and rear end plates are screwed onto the manifold
and should not need to be removed. The GC/MSD interface
fastens to the manifold with three screws.
The calibration valve assembly is fastened onto the front end
plate by two screws. The vent valve knob threads into the front
end plate. Small O-rings in grooves in the front end plate
provide vacuum seals.
The diffusion pump baffle adapter has a groove for its O-ring.
The baffle adapter is clamped to the manifold with four claw
grips.
KF (NW) seals
Most of the seals for the high vacuum pumps, foreline gauge,
and foreline pump are KF seals. KF seals have an O-ring
supported by a centering ring. The centering ring can be either
on the inside or the outside of the O-ring. The clamp presses two
flanges against the O-ring, making a seal. KF clamps must not be
overtightened.