A pressure drop on the regulated low-pressure
gage indicates that the leakage on/off valve is
leaking. This completes your leakage check. You
must bleed the system by turning the high-pressure
regulator to the VENT position until the high-
-pressure gage reads zero and then open the system
bleed valve. This bleeds all remaining lines.
The purpose of the regulated low-pressure
nitrogen system is to supply regulated low-
pressure nitrogen to the N2 input connection and
the in-system leakage rotameters. This system,
shown in figure 2-5, has a range of 0 to 180 psig.
You adjust the pressure by using the mechanically
operated low-pressure regulator. When you open
the low-pressure regulator, nitrogen flows through
the one-way check valve to the back side of the
one-way check valve that protects the high-
A s n i t r o g e n e n t e r s t he
high-pressure lines, it flows to the inlet pressure
on/off valve, the systems bleed valve, the vent
pressure valve, and through the gage guard that
protects the in-systems leakage rotameters.
(Nitrogen also flows into the rotameters and to
the 200- to 230-psig relief valve. However, this
is not considered part of the low-pressure system.
For the nitrogen to flow to the item under test,
you have to open the inlet pressure on/off valve.
T h i s a l l o w s n i t r o g e n t o f l o w t o t h e i n p ut
connection inside the chamber where the item
under test is connected.
PRESSURIZING THE REGULATED
LOW-PRESSURE NITROGEN SYSTEM
When you pressurize the low-pressure nitrogen
system, be sure that the N2 input connection is
capped and the supply cylinder valve is open. Turn
the leakage selector valve to the HIGH position
and the pressure selector valve to the HG
position. Turn the inlet pressure and leakage
on/off valves to the ON position. Slowly turn the
l o w - p r e s s u r e r e g u l a t o r c l o c k w i s e u n t i l t he
regulated low-pressure gage and the N2 input gage
indicate 70 psig. (We use 70 psig because this is
the pressure used to calibrate the rotameter
system.) At this time, return the inlet pressure
on/off valve to OFF. There should be no leakage;
but if any leakage occurs, the small ball in the
high-range leakage rotameter tube will rise.
Figure 2-5.Model 1172AS100 regulated low pressure N2 system.