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APPENDIX A
TM 07661B-14/1
A 2-8. DRY CHEMICAL SYSTEM . The dry chemical system components are located on the left side of the skid frame
and includes the vertically-mounted tank at the center of the unit.
a.
Nitrogen Cylinder Discharge Valve. The nitrogen cylinder valve (1, figure 2-5) is the primary control for the
dry chemical system. This quick-opening valve is mounted on the outlet of the nitrogen N cylinder. Lifting the handle up
90 degrees completely opens the valve and pressurizes the system provided the charging valve in the system is in the
stand-by or open position. Pushing the handle down shuts off the nitrogen supply to the system.
b.
Nitrogen Cylinder Pressure Gage. The 0-3000 psi pressure gage (2, figure 2-5) installed on the quick-
opening valve attached to the outlet of the nitrogen cylinder is on the cylinder side of the cutoff. The gage gives a
continual reading of cylinder pressure, regardless of valve position. Normal reading on the gage when cylinder is fully
charged is 2400 psi at 700F. Minimum pressure indication for fire extinguisher operation is 1700 psi at 70F.
c.
Nitrogen Pressure Regulator. The pressure regulator (3, figure 2-5) for the dry chemical system is slightly
larger than the AFFF system regulator, to provide the larger volume of nitrogen needed for fluidizing the dry chemical
agent and filling the larger void in the dry chemical tank. The pressure regulator (3, figure 2-4) is mounted under the
hose reel frame and connected by high pressure hoses to the nitrogen cylinder and to the dry chemical system piping.
The function of the regulator is to reduce the high pressure nitrogen supply to system working pressure 230 psi. The
pressure regulator is pre-set at 230 psig and should not require readjustment in normal operation.
d.
Charge Valve. The charge valve (4, figure 2-5) controls the pressurization of the dry chemical tank. This
valve is kept in a normally open position to ensure the "ready" status of the extinguisher in event of fire. Normally, the
valve should be closed only when it is necessary to purge the dry chemical discharge and dispensing lines with nitrogen
directly from the nitrogen cylinder. With the charge valve closed, the lines can be purged without pressurizing the tank.
e.
Purge Valve. The dry chemical purge valve (5, figure 2-5) controls the tank bypass line and permits purging
of the discharge lines and dispensing hose with nitrogen directly from the nitrogen cylinder. This valve is normally closed
except when necessary to apply additional nitrogen pressure if tank top pressure is insufficient to purge the lines.
f.
Dry Chemical Control Rod. Located at the front of the unit, the dry chemical control rod (6, figure 2-5) puts
the dry chemical shutoff valve within easy reach for quick actuation of the dry chemical system. The rod connects
through a u-joint to the dry chemical shut-off valve on the outlet of the dry chemical tank. Turning the control rod 90
degrees counterclockwise fully opens the discharge line of the dry chemical tank. To stop the product discharge, the
valve rod is returned to the closed position.
g.
Twin Agent Nozzle. The dry chemical nozzle (7, figure 2-5) is the right hand nozzle of the twin
A 2-10
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