FIGURE 9-8. HOSE ASSEMBLY INSTRUCTIONS (CAN BE USED FOR
LOW-PRESSURE HYDRAULIC FLUID, AND OIL LINE APPLICATIONS)
LOCATE AND SLIT
COYER WITH KINFE
TO WHE BALLO
TWIST OFF
COVER WITH PLIERS
1. Place hose in vise fine tooth 2. Locate length of hose to be cut desired length using fine off and slit cover with knife to wire hacksaw or cut off wheel. braid. After slitting cover, twist off with pair of pliers. (see note below)
3. Place hose in vise and screw 4. *Lubricate inside of hose and socket on hose counterclockwise. nipple threads liberally.
NOTE:
Hose assemblies fabricated per MIL-H-8790 must have the exposed wire braid coated with a special sealant.
5. Screw nipple into socket using wrench on hex of nipple and leave .005 inches to .031 inches clearance between nipple hex and socket.
NOTE:
Step 2 applies to high pressure hose only.
*CAUTION:
Do not use any petroleum product with hose designed for synthetic fluids,iSKYDROL and /or HYJET product. For a lubricant during assembly use a vegetable soap liquid.
DISASSEMBLE IN REVERSE ORDER Par 9-30 Page 9-25
Par 9-30 Page 9-26 TABLE 9-3. AIRCRAFT HOSE SPECIFICATIONS
SINGLE WIRE BRAID FABRIC COVERED MIL. PART NO.
TUBE SIZE OD HOSE SIZE ID HOSE SIZE OD RECOMM OPER.
PRESS.
MIN.
BURST PRESS.
MAX.
PROOF PRESS.
MIN BEND RADIUS MIL-H-8794-3-L 3/16 1/8 .45 3,000 12,000 6,000 3.00 MIL-H-8794-4-L 1/4 3/16 .52 3,000 12,000 6,000 3.00 MIL-H-8794-5-L 5/16 1/4 .58 3,000 10,000 5,000 3.38 MIL-H-8794-6-L 38 5/16 .67 2,000 9,000 4,500 4.00 MIL-H-8794-8-L 1/2 13/32 .77 2,000 8,000 4,000 4.63 MIL-H-8794-10-L 5/8 1/2 .92 1,750 7,000 3,500 5.50 MIL-H-8794-12-L 3/4 5/8 1.08 1,750 6,000 3,000 6.50 MIL-H-8794-16-L 1 7/8 1.23 800 3,200 1,600 7.38 MIL-H-8794-20-L 1 1/4 1 1/8 1.50 600 2,500 1,250 9.00 MIL-H-8794-24-L 1 1/2 1 3/8 1.75 500 2,000 1,000 11.00 MIL-H-8794-32-L 2 1 13/16 2.22 350 1,400 700 13.25 MIL-H-8794-40-L 2 1/2 2 3/8 2.88 200 1,000 300 24.00 MIL-H-8794-48-L 3 3 3.56 200 800 300 33.00 Construction: Seamless synthetic rubber inner tube reinforced with one fiber braid, one braid of high tensile steel wire and covered with an oil-resistant rubber impregnated fiber braid.
Uses: Hose is approved for use in aircraft hydraulic, pneumatic, coolant, fuel and oil systems.
Identification: Hose is identified by specification number, size number, quarter year and year, hose manufacturer’s identification.
Operating Temperatures:
Sizes—3 through 12:
Minus 65 °F to plus 250 °F Sizes—16 through 48:
Minus 40 °F to plus 275 °F Note: Maximum temperatures and pressures should not be used simultaneously.
Par 9-30 Page 9-27 TABLE 9-3. AIRCRAFT HOSE SPECIFICATIONS (CONTINUED)
MULTIPLE WIRE BRAID RUBBER COVERED MIL PAR NO.
TUBE
SIZE OD HOSE
SIZE ID HOSE SIZE OD RECOMM OPER.
PRESS.
MIN.
BURST PRESS.
MIN.
PROOF PRESS.
MIN.
BEND RADIUS MIL-H-8788-4-L 1/4 7/32 0.63 3,000 16,000 8,000 3.00 MIL-H-8788-5-L 5/16 9/32 0.70 3,000 14,000 7,000 3.38 MIL-H-8788-6-L 3/8 11/32 0.77 3,000 14,000 7,000 5.00 MIL-H-8788-8-L 1/2 7/16 0.86 3,000 14,000 7,000 5.75 MIL-H-8788-10-L 5/8 9/16 1.03 3,000 12,000 6,000 6.50 MIL-H-8788-12-L 3/4 11/16 1.22 3,000 12,000 6,000 7.75 MIL-H-8788-16-L 1 7/8 1.50 3,000 10,000 5,000 9.63 Hose Construction: Seamless synthetic rubber inner tube reinforced with one fabric braid, two or more steel wire braids, and covered with a synthetic rubber cover (for gas applications request perforated cover).
Uses: High pressure hydraulic, pneumatic, coolant, fuel and oil.
Operating Temperatures:
Minus 65 °F to plus 200 °F Identification: Hose is identified by specification number, size number, quarter year and year, hose manufacturer’s identification.
FIGURE 9-9. PROPER HOSE INSTALLATIONS
RIGHT WAY WRONG WAY Do not bend or twist the hose as illustrated.
Allow enough slack in the hose line to provide for changes in length when pressure is applied. The hose will change in length from + 2% to - 4%.
Metal end fittings cannot be considered as part of the flexible portion of the assembly.
The use of elbows and adapters will ensure easier installation and in many installations will remove the strain from the hose line and greatly increase service life.
At all times keep the minimum bend radii of the hose as large as possible to avoid tube collapsing.
Par 9-30 Page 9-28
FIGURE 9-10. MINIMUM BEND RADII
- 3 INSIDE BEND RADII V.S. OPERATING PRESSURE MIL-H-8794 HOSE WITH NO FLEXING 12 - 10 20 200 600 800 1000 1500 2000 2500 3000 OPERATING PRESSURE - POUNDS/SQ. IN. (-3 TO -24 INCLUSIVE) IRES ARE AS FOLLOWS:
MIL-H-STER HOLE WITH 40 NO FLEXING - 48 DASH NO. SEND RADI
3.000
3.375
5.000 3750
4.500 0 #D 100 120 140 160 180 7350
9.415
TOTAL FLEXING RANCE OF INSTALLED HOSE (DEGREES) MINIMUM BEND RADIUS OF HOSE UNDER FLEXING CONDITIONS = "N" X NO FLEXING BEND RADIUS OF EITHER MIL-H-8794 OR MIL-H-8788 HOSE EXAMPLE: FOR MIL-H-8794 HOSE (MEASURED AT INSIDE OF BEAD). RADIUS
MININUM BEND RADI MEASURED AT INSIDE OF BEND DIMENSIONS IN INCHES.
Par 9-30 Page 9-29
Par 9-30 Page 9-30
(1) Teflon hose is used in many aircraft systems because it has superior qualities for certain applications. Teflon is compounded from tetrafluoroethylene resin which is unaffected by fluids normally used in aircraft. It has an operating range of -65 °F to 450 °F. For these reasons, Teflon is used in hydraulic and engine lubricating systems where temperatures and pressures preclude the use of rubber hose. Although Teflon hose has excellent performance qualities, it also has peculiar characteristics that require extra care in handling. It tends to assume a permanent set when exposed to high pressure or temperature. Do not attempt to straighten a hose that has been in service. Any excessive bending or twisting may cause kinking or weakening of the tubing wall. Replace any hose that shows signs of leakage, abrasion, or kinking. Any hose suspected of kinking may be checked with a steel ball of proper size. Table 9-4 shows hose and ball sizes. The ball will not pass through if the hose is distorted beyond limits.
TABLE 9-4. BALL DIAMETERS FOR TESTING HOSE RESTRICTIONS OR KINKING
HOSE SIZE BALL SIZE -4 5/64 -5 9/64 -6 13/64 -8 9/32 -10 3/8 -12 1/2 -16 47/64 -20 61/64
(2) If the hose fittings are of the reusable type, a replacement hose may be fabricated as described in Figure 9-8. See Figure 9-10 for minimum bend radii. When a hose assembly is removed, the ends should be tied as shown in Figure 9-11, so that the preformed shape will be maintained. See Figure 9-12 for minimum bend radii for Teflon hose.
Par 9-30 Page 9-31 FIGURE 9-11. SUGGESTED HANDLING OF PREFORMED HOSE
Par 9-30 Page 9-32 FIGURE 9-12. MINIMUM BEND RADII–TEFLON HOSE (
3) All flexible hose installations should be supported at least every 24 inches. Closer supports are preferred. They should be carefully routed and securely clamped to avoid abrasion, kinking, or excessive flexing. Excessive flexing may cause weakening of the hose or loosening at the fittings.
e. O-Ring Seals. An understanding of O-ring seal applications is necessary to determine when replacement should be made. The simplest application is where the O-ring merely serves as a gasket when it is compressed within a recessed area by applying pressure with a packing nut or screw cap. Leakage is not normally acceptable in this type of installation. In other installations, the O-ring seals depend primarily upon their resiliency to accomplish their sealing action. When moving parts are involved, minor seepage may be normal and acceptable. A moist
Par 9-30 Page 9-33 surface found on moving parts of hydraulic units is an indication the seal is being properly lubricated. In pneumatic systems, seal lubrication is provided by the installation of a grease-impregnated felt wiper ring. When systems are static, seepage past the seals is not normally acceptable.
f. Storage of Replacement Seals.
(1) Store O-ring seals where temperature does not exceed 120 °F.
(2) Keep seals packaged to avoid exposure to ambient air and light, particularly sunlight.
g. During inspection, consider the following to determine whether seal replacement is necessary.
(1) How much fluid is permitted to seep past the seals? In some installations minor seepage is normal. Refer to the manufacturer’s maintenance information.
(2) What effect does the leak have on the operation of the system? Know the system.
(3) Does the leak of fluid create a hazard or affect surrounding installations? A check of the system fluid and a knowledge of previous fluid replenishment is helpful.
(4) Will the system function safely without depleting the reservoirs until the next inspection?
h. Dos and Don’ts that Apply to O-Ring Seals.
(1) Correct all leaks from static seal installations.
(2) Don’t retighten packing gland nuts; retightening will, in most cases, increase rather than decrease the leak.
(3) Never reuse O-ring seals because they tend to swell from exposure to fluids and become set from being under pressure. They may have minor cuts or abrasions that are not readily discernible by visual inspection.
(4) Avoid using tools that might damage the seal or the sealing surface.
(5) Do not depend upon color-coding. Coding may vary with manufacturer.
(6) Be sure that part number is correct.
(7) Retain replacement seals in their package until ready for use. This provides proper identification and protects the seal from damage and contamination.
(8) Assure that the sealing surfaces are clean and free of nicks or scratches before installing seal.
Par 9-30 Page 9-34
(9) Protect the seal from any sharp surfaces that it may pass over during installation.
Use an installation bullet or cover the sharp surfaces with tape.
(10) Lubricate the seal so it will slide into place smoothly.
(11) Be sure the seal has not twisted during installation.
i. Hydraulic System Pressure Test. When a flexible hose has been repaired or overhauled using existing hardware and new hose material, before the hose is installed on the aircraft it is recommended that the hose is tested to at least 1.5 system pressure. A new hose can be operationally checked after it is installed in the aircraft using system pressure.
j. Hydraulic Components. Hydraulic components such as pumps, actuating cylinders, selector valves, relief valves, etc., should be repaired or adjusted following the airplane and component manufacturer’s instructions. Inspect hydraulic filter elements at frequent intervals and replace as necessary.
9-31. –9-36 [RESERVED.]
Par 9-37 Page 9-35 SECTION 3. EMERGENCY EQUIPMENT
9-37. LIFE RAFTS. Inflatable life rafts are subject to general deterioration due to aging.
Experience has indicated that such equipment may be in need of replacement at the end of 5 years due to porosity of the rubber-coated material. Wear of such equipment is accelerated when stowed on board aircraft because of vibration which causes chafing of the rubberized fabric. This ultimately results in localized leakage. Leakage is also likely to occur where the fabric is folded because sharp corners are formed. When these corners are in contact with the carrying cases or with adjacent parts of the rubberized fabric, they tend to wear through due to vibration (refer to TSO-C70b).
a. When accomplishing maintenance, repair, and inspection of unpacked rafts, personnel should not step on any part of the raft or flotation tubes while wearing shoes. Rafts should not be thrown or dropped, since damage to the raft or accessories may result. Particular care should be exercised at all times to prevent snagging, cutting, and contact with gasoline, acids, oils, and grease. High standards of performance for proper maintenance, inspection, and repair cannot be overemphasized, since the lives of passengers could be involved.
b. Inspection and inflation tests, when applicable, will be accomplished during storage and after installation in an aircraft in accordance with the manufacturer’s specifications and/or FAA-approved procedures. Accessory items will be installed during these inspections. A raft knife will be attached by a 24-inch nylon lanyard to the mooring eye located above the carbon dioxide (CO2) cylinder case to enable rapid cutting of the mooring line.
9-38. LIFE RAFT INSPECTIONS. Inspection of life rafts should be performed in accordance with the manufacturer’s specifications. General inspection procedures to be performed on most life rafts are as follows.
CAUTION: Areas where life rafts are inspected or tested must be smooth, free of splinters, sharp projections, and oil stains. Floors with abrasive characteristics, such as concrete or rough wood, will be covered with untreated tarpaulins or heavy clean paper.
a. Inspect life rafts for cuts, tears, or other damage to the rubberized material. If the raft is found to be in good condition, remove the CO2 bottle(s) and inflate the raft with air to a pressure of 2 psi. The air should be introduced at the fitting normally connected to the CO2 bottle(s). After at least 1 hour, to allow for the air within the raft to adjust itself to the ambient temperature, check pressure and adjust, if necessary, to 2 psi and allow the raft to stand for 24 hours. If, after 24 hours, the pressure is less than 1 psi, examine the raft for leakage by using soapy water. In order to eliminate pressure variations due to temperature differences at the time the initial and final reading are taken, test the raft in a room where the temperature is fairly constant. If the pressure drop is satisfactory, the raft should be considered as being in an airworthy condition and returned to service after being fitted with correctly charged CO2 bottles as determined by weighing them. Rafts more than 5 years old are likely to be unairworthy due to deterioration. It is suggested that serviceable rafts be marked to indicate the date of inspection and that soapstone be used when folding them preparatory to insertion into the carrying case. Take care to see that all of the raft’s required equipment is on board and properly stowed. If the raft lanyard, used to
Par 9-38 Page 9-36 prevent the raft from floating away from the airplane, is in need of replacement, use a lanyard not less than 20 feet long and having a breaking strength of about 75 pounds.
b. It is recommended that the aforementioned procedure be repeated every 18 months using the CO2 bottle(s) for inflation. If a single bottle is used for inflating both compartments, it should be noted whether the inflation is proceeding equally to both compartments. Occasionally, the formation of “carbon-dioxide snow” may occur in one passage of the distribution manifold and divert a larger volume of gas to one compartment, which may burst if the mattress valve is not open to relieve the pressure. If the pressure is satisfactory, return the raft to service in accordance with the procedure outlined.
c. Inspect the CO2 cylinder for evidence of cross-threading or stripping.
d. Inspect the CO2 bottle inflation valve cable rigging as follows.
(1) Remove the screws that attach the cover plate to the valve and remove the cover plate.
(2) Inspect the firing line cable ball swage for engagement in the correct recess for either “Upward Pull” or “Downward Pull.” The cable will be wrapped around the sheave approximately 270 degrees.
(3) Reposition the cable ball swage as required. (See Figure 9-13.)
(4) Replace the cover plate. The green dot on the sheave should be visible through the window in the cover plate, indicating a charged cylinder.
e. Check the CO2 cylinder release cable and housing for condition and security.
f. Make sure the safety deflector is removed from the cylinder outlet before connecting the cylinder to the raft. (See Figure 9-13.)
g. Stencil the life raft’s inspection date on the raft.