TM 55-6610-247-40
Table 2-6. Adjustment Tolerance
STANDARD
EQUIVALENT
SCALE ERROR
ALTITUDES
ATMOSPHERIC PRESSURE
TOLERANCE
MERCURY
FEET
MM
INCHES
FEET
0
760.0
29.92
20
500
746.4
29.39
20
1.000
732.9
28.86
20
1,500
719.7
28.33
25
2,000
706.6
27.82
30
2,500
693.8
27.31
30
3,000
681.1
26.81
30
4,000
656.3
25.84
35
5,000
632.4
24.89
40
20,000
349.1
13.75
130
35,000
178.7
7.04
350
on center pinion as hand staff can
2-10. Replacing Mechanism in Case.
a. Press retaining ring (38, figure 21) into lowest
easily be broken.
groove with locating nib in slot at top of case.
f. Place a 0.005-inch-thick slotted shim on boss of
b. Place ring spring 134 on a flat surface. Note that
casting with hand staff in slot. With tweezers, press
there are three high points located 1200 apart. Spring
center pinion, hub up, onto hand staff until it rests against
should be placed in case so that of three high points, one
shim.
at locating nib faces out toward dial. There are three
g. Replace wheel assembly, pinion up, so gear is in
pads or high spots on underside of top plate mechanism
mesh with center pinion. Lower top bearing plate onto top
assembly 134). These pads should be matched with high
plate insuring wheel assembly is in mesh with hand-staff
points on ring spring. With units assembled in case in
pinion and wheel assembly pivot is in pivot hole.
this manner, stresses on mechanism body will be evenly
h. Lightly press short hand onto hand staff. While
distributed and potential source of barometric pressure
holding top bearing plate in place with finger, lightly flick
errors will be eliminated.
end of hand. An oscillating, springlike resistance to
b.l. Place shim (36A) on top of ring spring (37).
movement indicates correct assembly. Secure top
c. Lower mechanism assembly 136) into case so
bearing plate to top plate with screws.
sector counterweight is next to adjustment knob pinion.
2-11. Operation Check.
NOTE
Operational check is as follows:
Do not replace mechanism top plate
a. Press long hand onto hand staff and place
assembly (34) with top bearing plate or
mechanism in pressure chamber, part no. 16 112.
wheel assembly assemblied. First
b. Decrease pressure at a rate of 3,000 feet per
remove these parts.
minute until an indication of 30,000 feet is reached, them
allow pressure to return to room pressure at same rate.
d. Replace mechanism top plate so aligning pin is in
The hand should move smoothly. A slight hesitation is
sIot of case. Press it down so hole in top plate. fits over
permissible but hand should not hang on an indication,
loss of mechanism body. Secure top plate with retaining
then suddenly jump to the next point. During this check,
ring (33). Replace spring (32) directly opposite knob
instrument should be vibrated.
stem.
c. If any friction is apparent, it is in top plate
e. With a test knob on knob stem, check action of
mechanism assembly. Determine cause of malfunction
parts by rotating mechanism assembly. Action should be
by disassembling top plate mechanism and examining
smooth and slightly stiff without any binding. Improper
for oxidation or dirt on hand-staff bushing assembly,
action of mechanism assembly may be caused by too
bearing holes, and pivots. Also examine gear teeth for
tight a mesh between pinion (43) and gear on
burrs or damage.
mechanism body.
CAUTION
Excessive force shall not be used in
pressing
2-16
