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737-300/400/500MAINTENANCE MANUAL
(c) If the external leak location is the boundary between the wing tank and the center tank, look for leaks in these two tanks (Fig 601).
NOTE: It is a good procedure to put one person in the wing
____ tank and one person in the center tank. These two persons must look for internal leaks in the fillet seals on each side of the rib. Examine the full length of all of the fillet seals. It is possible for the head pressure of the fuel in the tank to cause fuel to show at an external location that is higher than the internal leak location.
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(7) The person in the tank must tell the person out of the tank when to blow air through the external leak.
NOTE:____Agree on a system of knocks. For example, the person in the tank knocks one time to start the backblowing, two times if he finds the leak, three times if the leak is not found.
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(8) The person out of the tank must use an air supply with a nozzle to blow air through the external leak location (Fig. 604).
NOTE: The external leak location can be a hole in the
____ aerodynamic smoother, a bad fastener, or an open seam in one of the spars, or the side-of-body rib.
(a)
If the leak is small, it can be necessary to use the maximum pressure (100 psi, 690 kPa).
(b)
If the leak is larger, it is easier to find the leak with less pressure (for example, 50 psi [340 kPa] or less).
(c)
Look for bubbles that show the location of the leak.
(d)
It is also possible to feel for blowing air to find the leak.
(e)
Find all leak locations on the internal surface of the fuel tank.
NOTE: It is possible that three or four internal leaks are
____ related to one external leak location. Make a signal to the person out of the tank to stop the backblowing procedure when you find all of the leaks.
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