Repair Of Sub-Assemblies; Piston/Diaphragm Sub-Assembly - Agilent Technologies VPI Series Instruction Manual

4. Inspect the nose piece
imbedded with foreign material

3.2 Repair of Sub-Assemblies

3.2.1 Piston/Diaphragm Sub-Assembly

1. Remove the diaphragm
using a spanner wrench. Inspect the orifices and clean if necessary. Be careful not to
enlarge the orifices, because performance may suffer. Inspect the diaphragm
holes, tears, or accumulated contamination. Discard it if damaged.
2. Inspect the dry bushings
good for several hundred thousand cycles, but they can be replaced when they have
worn out. A worn bushing can be identified by excessive exposure of the sintered
bronze matrix, which is not normally visible. A modest amount of lead /PTFE flakes in
and around the bushing and pin is normal and does not constitute abnormal wear of the
bushing. If there is any doubt about the condition of the bushings, they should be
replaced. Remove by inserting a number 10 machine screw and pulling. There are two
¼ in. long bushings used in tandem. After removal of the old bushings inspect the bore
in the sleeve
the bore, one at a time, flush to the top of the sleeve.
3. To reassemble, place the diaphragm
outer bead up (Figure 6 on page 23). A small amount of vacuum compatible grease
should be smeared on the sleeve side of the diaphragm/sleeve contact area to prevent
puckering of the diaphragm during tightening of the sleeve. Also, if the piston and
sleeve have been degreased prior to assembly, a small amount of vacuum compatible
lubrication should be applied to the male threads of the sleeve to prevent seizing of the
sleeve to the piston. DuPont Krytox
tight. Do not overtighten, this is not a vacuum grade seal.
24
Vacuum Pump Isolation (VPI) Valve
O-ring carefully. It must be replaced if it is scratched or
from the piston by unscrewing the sleeve
pressed into the sleeve
for debris and burrs. Clean as necessary. Press two new bushings into
®
. These bushings are normally
on the piston with the inner bead down and the
GPL 206 is acceptable. Tighten the sleeve hand
from the piston
for