Agilent Technologies 7000 Triple Quadrupole GC/MS, Maintenance Manual

Page: 137 / 214

Vacuum System
6
Troubleshooting and Maintenance Manual 137
Vacuum Seals
Vacuum seals are shown in Figure 22 .
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. Three of the
O-rings are
lightly lubricated with Apiezon-L vacuum grease: the side plate
O-rings 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 plates 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 MS is turned on for pumpdown to ensure a good seal.
The front and rear end plates are screwed onto the manifold and should not
need to be removed. The GC/MS interface fastens to the manifold with three
screws.
The calibration valve assembly is fastened onto the front end of the manifold
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.
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.
Compression seals
A compression fitting consists of a threaded fitting on the analyzer chamber
and a threaded collar with a ferrule and O-ring. A cylindrical part fits inside
the collar. Tightening the collar presses the ferrule, compressing the O-ring
around the part. The calibration vials use compression seals.