rotameter tube, it indicates a leak. If no leakage
is indicated during this test, continue.
Return the leakage selector valve (F) to the
HIGH position and turn the leakage on/off valve
(G) to the OFF position. By slightly cracking the
cap at the N2 input connection, you can bleed any
pressure indicated on the N2 input pressure gage
(27)
At this time, a line with two bayonet fittings
must be attached between the low-pressure
connection (19) and the 200-CCM leakage con-
nection (20) inside the chamber. This line is used
to check for any leakage through the leakage
control valve (E). Leakage is indicated on the
o v e r b o a r d r o t a m e t e r ( G ) . I f n o l e a k a g e is
indicated, remove the side attached to the leakage
connection (20) and attach it to the reference tap
connection (21 ). (This sets your test stand up to
perform the differential pressure system test.) The
reference tap connection (21) is also located
i n s i d e t h e c h a m b e r . P l a c e a c a p o v e r t he
piezometer and turn the pressure selector valve
(D) to the H2O position. Slowly open the leakage
control valve (E) until the pressure/suction
manometer (4) indicates 9.0 inches of water (in.
H2O). Fully closing this valve (E) may be
necessary after you reach 9.0 in. H2O. No leakage
should be indicated on the high-range leakage
rotameter (8).
Turn the leakage selector valve (F) to the LOW
RANGE position. No leakage should be indicated
on the low-range leakage rotameter (7). Close the
leakage control valve (E) and turn the leakage se-
lector valve (F) to the HIGH RANGE position.
Now disconnect the line at the low-pressure con-
nection (19). Bleed the pressure from the pressure/
suction manometer (4); then reconnect the lines.
If you find this system has no leakage, your
test stand is set up to perform the differential
pressure indicating system leakage test.
DIFFERENTIAL PRESSURE
INDICATING SYSTEM
The schematic for the differential pressure
indicating system is shown in figure 2-7. The
purpose of this system is to sense the difference
in pressure between the outlet of the component
being tested and the surrounding atmosphere,
w h e t h e r a t s e a l e v e l o r a l t i t u d e . Y o u u se
this system when you perform safety-pressure,
pressure-breathing, and flow-suction tests. Three
manometers on the test stand indicate differen-
tial pressure: the pressure/suction manometer (4),
t h e H G m a n o m e t e r ( 5 ) , a n d t h e i n c l i n ed
pressure/suction manometer (25).
With the pressure selector valve (D) in the H2O
position, pressure or suction is sensed in the
Figure 2-7.—Model 1172AS100 differential pressure indicating system.
2-8
