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2. Test the combustion tube assembly for leaks as follows:
A.  Fashion a sealing plate from approximately 1/8 inch thick flat stock to seal the combustion head opening in the combustion tube assembly. (Refer to Figure 21-16) Use a rubber gasket under the.plate and attach the plate with six screws.
B.  Make up seals for all remaining openings, except the one used to connect the air pressure source. (Refer to Figure 21-16) Use rubber stoppers as shown.  The combustion air inlet tube can be sealed
best with a drilled stopper and clamp. Other openings should be sealed with expansion plugs. The seal used in the exhaust tube should be formed so that it will not deform the air pressure switch tube which protrudes into the exhaust.
C.  Install plugs and caps in all openings except the one to which the combustion air pressure switch is attached. (Any opening can be used to connect the air pressure source, however, the combustion air pressure switch opening is usually the most convenient.  The drain opening would normally be considered a second choice.)
D.  Connect a regulated air supply to the opening that has not been plugged and apply a pressure of between three and five psi to the combustion tube assembly.
E.  Submerge the combustion tube assembly in water for several minutes while watching for bubbles which would indicate leaks.  No air leakage is permitted from the combustion tube assembly.  No weld or braze repairs are permitted on a combustion tube assembly.
21-40-00 Page 21-43 Revised: February 28, 2002
3. Test the combustion air pressure switch as follows:
A.  Connect an adjustable air pressure line that can be controlled in a range of zero to 5.0 psi (maximum) of water to the switch opening with a water manometer and needle valve in the line ahead of switch. Switch must be tested in 45 degree position as shown in Figure 21-17.
B.  Connect an ohmmeter across the switch terminals to determine the exact instant of switch closing.
C.  Apply air pressure allowing it to build up very slowly from zero.  The switch contacts should close at 0.5 ± 0.1 inches of water which will be indicated on the manometer.
— Note —
The switch cover has a differential pressure tap and this opening must be left open to atmosphere during test.
D.  Make several trials to insure switch reliability.  Be sure to increase and decrease the air pressure slowly in order to produce accurate indications.
E.  If an adjustment is required, rotate the adjusting screw clockwise to increase settings and counterclockwise to decrease settings.
4. Test the fuel line and fuel line shroud tube for leaks as follows:
A.  Using filtered compressed air, apply 20 psi to the shroud drain port located on the surface near the threaded nozzle cavity.
B.  Immerse the fuel feed and nozzle holder assembly in clean water with the fuel inlet and nozzle cavity left open.
C.  Observe for bubbles which would indicate leakage.  If bubbles appear at either fuel fitting, there is a leak in the fuel tube. If bubbles appear externally on the shroud tube or at either end of the shroud tube juncture, the shroud tube is leaking.
D.  In either of the above cases, the complete fuel feed and nozzle holder assembly must be replaced.
5. Spray test the nozzle (refer to Figure 21-18) as follows:
A.  Install the nozzle in the fuel feed and nozzle holder assembly and connect the fuel tube to the fuel solenoid. Connect the solenoid to a 7 psi fuel pressure source.
B.  Connect the solenoid leads to a 12 volt battery. Connect a switch in the line to open and close the solenoid when desired.
— WARNING —
BE SURE TO KEEP THE ATOMIZED SPRAY AWAY FROM FIRE.

C.  With the switch closed (solenoid valve energized) and the fuel line connected, observe the fuel spray pattern. It should be conical in shape with even dispersion in all directions.
D.  Energize and de-energize the solenoid several times.  The spray should shut off permanently each time the solenoid is de-energized.  There should be no sign of dribbling at the nozzle tip in excess of one or two drops.
E.  If the spray pattern is distorted, check for an obstruction and clean the nozzle.  If this fails to provide a normal spray pattern, replace the nozzle.
F.  If the nozzle continues to dribble, the solenoid valve is not closing properly and the solenoid valve must be replaced.
21-40-00 Page 21-44
Revised: February 28, 2002

Figure 21-18. Exploded View of Heater Assembly 
21-40-00 
Page 21-45 
Revised: February 28, 2002 
1I19 

REPAIR OF COMBUSTION TUBE ASSEMBLY.
— Note —
No weld or braze repairs are authorized.

REASSEMBLY OF HEATER. (Refer to Figure 21-18)
　
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