Views: 5 Author: Site Editor Publish Time: 2020-02-08 Origin: Site
Piping and flexible hoses are used, among others,for hydraulic power transfer the control of vitally important aircraft systemssuch as nose and main landing gears, rudders and control surfaces, and assupply lines for fuel, oxygen etc. the installation of piping and flexiblehoses therefore requires utmost care.
Piping and flexible hoses taken from provisioningstore must be protected by caps, must have an inspection stamp and – unlessotherwise agreed – should be wrapped in protective foil. If protective caps aremissing or if the packing is damaged, they must be rejected for repeatedcleaning. Piping and flexible hoses must not show any signs of damage,corrosion or contamination.
The workplace and tools must be clean as even thesmallest traces of foreign particles can endanger the tightness of connections.
1. Minimum distances
Piping and flexible hoses shall be installed in sucha way that they do not touch one another or adjacent components.
If the minimum distances are not specified in themanufacturing documents, the distances specified in this process specificationshall apply.
For the minimum distances between piping/flexiblehoses and the structure, refer to Fig.1.
In case of components with relative movement, thespecified minimum distance (see Fig.2) shall be observed, even in the mostunfavorable state of movement.
For minimum distances between pipes and thestructure at attachment points, refer to Fig.3 and 4 and Table 1.
The minimum distance between clamp block/pipe clampand the beginning of the next pipe bend is 10 mm(see Fig.5).
For the minimum distance between individual pipes,refer to Fig.6, Table 2 and Table 3(only for hydraulics).
2. Protection against vibration and chafing
If the minimum distances between pipes specified inthe manufacturing documents cannot be observed, lacing tapes, spacers or clampsshall be used to avoid vibration and chafing.
Preference should be given to the installation ofclamps.
The tying or attachment points shall be marked onpipes by means of making tapes or marking varnish (red or white).
It is not permitted to tie hydraulic pipes withpipes of other systems (air, fuel, water etc.) or with electrical cableharnesses.
3. Handling of piping and flexible hoses during installation
Care shall be taken when transporting piping andflexible hoses from the provisioning store to the location of installation. Allprotective measures shall be taken to avoid damaging of piping and flexiblehoses. For this purpose, they shall be placed in special fixtures or on a softsurface (e.g. blankets or rubber mats).
4. If the work is interrupted or if the pipescannot be installed at this stage due to other jobs, re-install the protectivecaps.
5. Lubrication of threads, installation of seals etc.
6. Installation of piping and flexible hoses
When installing piping and flexible hoses, it mustbe taken into account that it is not permitted.
- Toplace objects (tools, test equipment, components etc.) on piping or flexiblehoses or to suspend objects from them.
- Todraw or to pull objects (tools, test equipment, components etc.) over piping orflexible hoses.
- Tograb hold of piping or flexible hoses and to sit, lie or stand on them.
7. Installation ofpipes with non-detachable connections during section assembly
The work steps –except d), e), f), i), and j) – shall be carried out as described in 5.8.1.
8. Installation of flexible hoses
Reinforced flexible hoses tend to kink easier than wired flexible hoses, this applies especially to hose sizes -12 and -16 and to flexible hoses of short lengths. The same applies to flexible hoses of size -20 and -24 with braids made of corrosion-resistant steel. Therefore , these flexible hoses shall be installedwith great care.
Hoses are identified with a yellow shrinkable sleeve marked "5.080 psi" or "1.000 ps".
If it must be suspected that flexible hoses have kinks, they shall be inspected for damage asshown in Fig. 25.
If damage as shown in Fig. 25 is detected, the inner PTFE hose shall be inspected. This is done withthe naked eye if the lighting conditions are sufficient. If this is notpossible, use must be made of instruments like borescopes.
If recesses or white folds are detected on the inner PTFE hoses or if an area appears to be unevenand not smooth, the hoses shall be replaced.
9. Installation of hoses
The flexible hoses shall be installed in such a way that they can not kink. The length of thestraight hose end next to the fitting must be at least twice the hose diameterin length. Twisting the hoses during installation must be avoided by all means.
The minimum bend radius given for flexible hoses must always be observed. The flexible hosesshall be bent slowly and carefully. As soon as the flexible hoses start toflatten in the bending area, the bending operation shall be stopped.
During installation,flexible hoses should be bent only in one direction to avoid twisting of theinner hose reinforcement. The bending operation should as far as possiblefollow the already existing hose bending direction to avoid kinks. 90°fittings shall bepositioned in hose bending direction before being tightened.
Flexible hoses should always be attached first at their less accessible end. This end should at firstbe tightened only manually. Install the hose correctly and tightened manuallythe other end of the hose as well. Then tighten the connections to thespecified torque for tightening screw connections of flexible hoses.
Use two jaw wrenches for straight fittings in plug-in unions or grommets. Use a jaw wtench totighten the union nut while using the other wrench to hole the hose hexagon toprevent a twisting of the hose. Three jaw wrenches shall be used for flexiblehoses not to be connected to plug-in unions or grommets.
After tightening andsuccessfully pressure testing screw connections, these shall be marked as described.