the pivot shaft. If your tech nique is cor rect, stretch ing the quad ring over the pivot shaft
should re quire only a light down ward pres sure.
CAU TION
Do NOT force the quad ring onto the pivot shaft. Doing so may
damage the quad ring, rendering it incapable of providing a
water-tight seal.
Step 6.
When you have pushed the lead ing edge of the quad ring past the wa ter out let slot, let go of
the backup washer and with draw your fin gers. Then push the mount ing flange all the way
down onto the pivot shaft.
Step 7.
Once the mount ing flange is all the way down on the pivot shaft, hold these two parts to -
gether and ro tate the mount ing flange un til the holes in the bear ing hous ing are lined up with
the threaded holes in the mount ing flange.
Step 8.
In stall the four 6-32
×
5/8-in. mount ing screws, snugging them down grad u ally in a cross -
wise pat ter to pre vent the bear ing hous ing from be com ing cocked in the mount ing flange’s
bore. Torque the mount ing screws to 8 in-.lbs.
Step 9.
Ro tate the pivot shaft by hand to make sure there is no bind ing as it turns.
Step 10.
Se cure the wa ter baf fle to the top of the pivot shaft, us ing the pan-head screws pro vided (see
Figure 6-12).
Step 11.
Check again for any trace of bind ing dur ing pivot shaft ro ta tion. This time, hold the mount -
ing flange in one hand and push the wa ter baf fle with one fin ger of the other hand to ro tate
the pivot shaft. The quad ring should pro duce a light, even re sis tance as the pivot shaft ro -
tates. If the re sis tance is heavy or un even, re move the mount ing flange from the bear ing
hous ing as sem bly and check to see that the quad ring has not be come cut or twisted. Check
also for parts that seem im prop erly in stalled or are out of tol er ance.
Be fore re in stall ing this as sem bly on the source base plate, ap ply low va por pres sure (Apiezon L or equiv a lent)
to the O-ring that fits be tween the base plate and the pivot shaft and place this O-ring in the groove in the bot -
tom of the pivot shaft.
Pro ce dure 6: Vac uum Leak Check of As sem bly
Per form this check af ter the gun is fully re as sem bled, ex cept for the cru ci ble cover.
Step 1.
Con nect the gun to a leak de tec tor with a sen si tiv ity of 1
×
10
-9
std. Atm cc/sec or better.
Step 2.
Ini ti ate the in stru ment’s test mode and note its base leak rate (i.e., its leak rate be fore he lium is
ap plied to the gun). This read ing in di cates whether there is any re sid ual he lium in the de tec tor
that should be re moved be fore you test the gun. Al ter na tively, the base rate can be sub tracted
from the test read ing.
Step 3.
Ap ply he lium to all the ex ter nal sur faces of the gun while ob serv ing the leak rate, which
should not ex ceed 3
×
10
-9
std. Atm cc/sec at any point.
Source Disassembly
STIH-270-2PT
0101-9004-0A
5-20
