(6)
Do one of the following steps:
(a)
Build a custom compression chamber around the external leak point with a plastic film.
(b)
If it is possible, install one of the pressure cups supplied in the Helitest Wing Kit to contain the helium pressure on the outer tank surface.
(7)
Install tape (SM5126 or SM5127) around the leak area or the pressure cup.
(8)
If building a custom chamber, do the following steps:
(a)
Cut a piece of material, L-P-512, to the size of the chamber formed by the tape, SM5126 or SM5127.
(b)
Set the plastic over the vacuum tape.
(c)
Work the plastic to make sure it sticks well to the vacuum tape.
(d)
Make sure the chamber is as small as possible.
NOTE: A small chamber can contain more helium pressure than a larger one.
(e)
Trim the plastic with a razor knife following the outline of the vacuum tape.
(9)
Do the following steps to connect the helium supply to the custom chamber:
(a)
Wrap the helium injection tube with vacuum tape to form a 2-inch diameter flange 1 to 2 inches from the end of the tube.
(b)
Slice a small hole in the plastic chamber and put the helium tube in the hole.
(c)
Work the vacuum tape flange on the injection tube so it sticks well and seals the plastic chamber.
(10)
If using a pressure cup, attach the helium injection tube to the cup with the fittings supplied in the kit.
(11)
Apply tape, 3M #434 or equivalent, over the plastic chamber or pressure cup and work it well for the best adhesion.
(a) Use a sufficiently large quantity of tape, 3M #434, to reinforce the plastic helium chamber so it can handle more pressure.
(12)
Set up the Helitest Wing Kit and purge the lines with helium to remove air.
(13)
Carefully and slowly apply about 0.2 psig helium pressure to the chamber.
NOTE: Start with low pressure and then slowly increase the pressure. Less helium is necessary for larger leaks than for smaller leaks. Too much helium will flood the fuel tank. Inspect the chamber of rubber cub to make sure there is no leakage. If it leaks too much, rebuild the chamber because the helium can interfere with the detector.
(14)
Put negative ventilation around the helium chamber to draw away leaking helium to make sure it does not interfere with the detector by drifting into the tank.
NOTE: This step is important for successful leak detection. Use positive pressure if negative pressure is not available, but make sure the helium is removed from the area and does not go into the tank where the detector probe is used.
(15)
Permit the helium to soak into the leak path into the leak path for 10-15 minutes before tank entry.
NOTE: Refer to the instructions supplied with the kit.
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NOTE: Time is necessary to push the remaining fuel out of the tank path and start the flow of helium from the external leak point to the internal leak point.
WARNING: KEEP THE DETECTOR AND THE PUMP AWAY FROM THE TANK. INJURY TO PERSONS AND DAMAGE TO EQUIPMENT CAN OCCUR.
(16)
The Helitest detector and the auxiliary pump must be kept away from the open fuel tank at all times.
(17)
Enter the tank with the Helitest Visual Probe (intrinsically safe for Class I, Div I areas).
(18)
Slowly interrogate the inside of the tank around the expected area of the leak.
NOTE: Patience is important. With a systematic approach, slowly move away from the suspected leak area until the exact leak location is found.
CAUTION: DO NOT PUT THE PROBE INTO FUEL PUDDLES. IT CAN CAUSE DAMAGE TO THE INSTRUMENT.
(19) If there is a puddle of fuel in the suspected leak area, use compressed air to dry the area.
(a)
Build rag dams to soak up additional running fuel.
(b)
Completely dry hidden areas.
(c)
If fuel is drawn into the Helitest probe, immediately remove the probe to a safe area and permit the probe to operate until all the fuel is vaporized. 1) Disconnect the visual probe gas line and permit it to run dry also. 2) Replace the wet filter on the visual probe tip with a dry filter. 3) Do not shut the Helitest off while contaminated with fuel because permanent
damage can occur.
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(20) If the leak is not found, increase the helium pressure to 0.6 psig, and then 1.2 psig.
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