10
Vacuum Sentry
TM
safety Valve
2.
Prepare the new seal by smearing a very light but continuous coat
of a vacuum compatible grease on the O-ring. We recommend
DuPont KRYTOX
R
GPL 206, which is a high quality fluorinated
grease offering low vapor pressure, excellent temperature stability
and is chemically inert. It is important to not skip this step. Tests
have indicated that a dry O-ring nose piece O-ring used in a valve
that has been closed for more than two hours is subject to a
breakaway friction exceeding the modest return spring force.
Note that the return spring has intentionally been designed to
be soft so as to minimize the opening pressure burst, thereby
necessitating a boundary layer lubrication at the nose piece
O-ring to control the breakaway friction between the valve seat
and the O-ring.
3. To replace the seal, position the piston (4) so that the
groove faces upward. Be sure that the bottom of the groove
and surfaces of the new O-ring are free of scratches. If
necessary, a suitable solvent may be used to clean the
groove. Particulate contamination may be blown off with
DUST-OFF
R
or dry nitrogen. Place the prepared O-ring
from step #2 above on top of the groove. Place two thumbs
on the o-ring at points 180
o
apart, and push the o-ring into
the groove. Avoid twisting the O-ring as it is pushed in.
Then push in the opposite intermediate points, and so on,
until the ring is uniformly in place.
Bonnet Subassembly
1.
The bonnet subassembly consists of the bonnet (10), guide
pin (1), and a solenoid valve (18) with fittings. The pin is
press fit into the bonnet. The pin is not replaceable,
therefore if the guide pin is bent, heavily scored, or loose
then the bonnet and the pin will need to be replaced as a
unit by a factory replacement part.
2.
If necessary, the solenoid valve (18) may be removed by
unscrewing from the bonnet. Inspect the small O-ring and
seal surfaces for damage. Replace if damaged.
Reassembly
1. Slide the piston / diaphragm subassembly on guide pin (1).
With the piston (4) facing up so it does not slide off of the
guide pin, place the body (7) down over the piston, flat
surface to the diaphragm. Now invert the body with the
bonnet held close and align the bolt holes. Insert six
10-32 x 7/8 socket head cap screws (9) and tighten to 27
inch-lb torque.
