AIRCRAFT FUNCTIONAL TESTING AFTER REPAIR

FUNCTIONAL TESTING AFTER REPAIR

Following repair, and before in­spection plates, cover plates, or upholstering are replaced, test the entire system.

Open the cylinder valve slowly and observe the pressure gauge on a high-pressure system. A pressure of approximately 1,800 psi (at 70 °F) should be indicated on the gauge. (Cylinder pressure will vary considerably with radical temperature changes.)

(1)       Check the system by installing one of the mask hose fittings (minus the mask) in each of the cabin wall outlets to determine whether there is a flow. If a demand mask is used, check by breathing through the mask and, if appropriate, clean the mask according to paragraph 7.9.4.

(2)       Check the complete system for leaks in accordance with the procedure outlined in paragraph 9-49b(2)(d).

(3)       If leaks are found, close the cylinder valve and open an outlet to reduce the pressure in the system to zero.

The following checks may be made for a pressure drop check of the system.

(1)       Open the cylinder valve and pres­surize the system. Observe the pressure gauge (a pressure of approximately 1,800 psi at 70 °F should be indicated). For the light weight ICC 3HT 1850 cylinders, pressurize the sys­tem to approximately 1,850 psi at 70 °F.

(2)       Close the cylinder valve and wait approximately 5 minutes for temperatures to stabilize.

(3)       Record the pressure gauge reading and temperature and after 1 hour, record the pressure gauge reading and temperature again.

(4)       A maximum pressure drop of 100 psi is permissible.

NOTE: Conduct the above tests in an area where changes of temperature will be less than 10 °F. If a leak oc­curs during the 1-hour period, suit­able corrections would be required, or reconduct the test under conditions of unvarying temperatures.

SERVICE REQUIREMENTS OXYGEN CYLINDERS: Standard-weight cylinders must be hydrostatic tested at the end of each 5-year period. This is a Department of Transportation (DOT) requirement. These cylinders carry an ICC or DOT 3AA 1800 classification and are suitable for the use in­tended: The lightweight cylinders must be hy­drostatic tested every 3 years, and must be re­tired            from    service           after    24 years         or 4,380 pressurizations, whichever occurs first. These cylinders carry an ICC or DOT 3 HT 1850 classification and must be stamped with the approval after being in­spected.

CAUTION: Use only aviation breathing oxygen when having the oxygen bottle charged.

Charging High-Pressure Oxygen Cylinders: The following are recommended procedures for charging high-pressure oxygen cylinders from a manifold system, either per­manently-installed or trailer-mounted.

CAUTION: Never attempt to charge a low-pressure cylinder directly from a high-pressure manifold system or cylinder.

(1)       Inspection. Do not attempt to charge oxygen cylinders if any of the follow­ing discrepancies exist:

(a)    Inspect for contaminated fittings on the manifold, cylinder, or outside filler valve. If cleaning is needed, wipe with stabilized trichloroethylene and let air dry. Do not permit the solvent to enter any internal parts.

(b)    Check the hydrostatic test date of the cylinder. DOT regulations require ICC or DOT 3AA designation cylinders to be hydro­static tested to 5/3 their working pressure, every 5 years. Cylinders bearing designation ICC or DOT 3HT must be hydrostatic tested to 5/3 their working pressure every 3 years, and retired  from service15 years or 4,380 filling cycles after the date of manufac­ture, whichever occurs first.

(c)    If the cylinder is completely empty, do not charge. An empty cylinder must be removed, inspected, and cleaned before charging.

(2)       Charging:

(a)    Connect the cylinder valve outlet or the outside filler valve to the manifold.

(b)    Slowly open the valve of the cylinder to be charged, and observe the pres­sure on the gauge of the manifold system.

(c)    Slowly open the valve of the cyl­inder on the manifold system having the low­est pressure and allow the pressure to equalize.

(d)    Close the cylinder valve on the manifold system and slowly open the valve of the cylinder having the next highest pressure. Continue this procedure until the cylinder has been charged in accordance with 

.

(e)    Close all valves on the manifold system.

(f)     Close the valve on the filled cyl­inder and remove the cylinder from the mani­fold.

(g)    Using a leak detector, test for leakage around the cylinder valve threaded connections. (If leakage is present, discharge the oxygen and return the cylinder to the facil­ity for repair.)

(h)    Let the cylinder stabilize for a pe­riod of at least 1 hour, and then recheck the pressure.

(i)      Make any necessary adjustments in the pressure.

Charging of Low-Pressure Oxygen Systems and Portables. For recharging a low-pressure aircraft oxygen system, or port­able cylinders, it is essential that the oxygen trailer or cart have a pressure-reducing regu­lator. Military types E-2 or C-1 reducing regulators are ` satisfactory. These types of regulators reduce the large cylinder pressure from 2,000 psi to a line pressure of 450 psi. (A welding pressure-reducing regulator is not satisfactory.)

CAUTION: When refilling the low pressure system or portable cylinders, open the oxygen filler tank valve slowly to allow the system or portable cylinders to be filled at a slow rate. After the refilling operation is com­pleted, check for leaks with a leak de­tector.