THE HONG KONG GOVERNMENT GAZETTE, DECEMBER 10, 1937.
4. The following precautions should also be taken in connection with the fitting of flexible tubing:-
(i) Before installing the tubing, it is essential to ensure that there are no restrictions or particles of foreign matter in the bore, and the tubes should be washed out with petrol before assembly.
(ii) Each section of flexible tubing must be adequately supported along its length, and provision must be made to prevent chafing of the tube against metal fittings.
(iii) The protective paint on the outer coverings of Petro-flex and Superflexit is liable to wear off in service, and if this occurs, a coating of seaplane varnish or other approved protective coating is to be applied.
(iv) Where radio is fitted, care should be taken to see that the flexible tubing is electrically bonded. Lengths of Petro-Flex and Superflexit tubing are bonded through their end fittings, in the case of the former by means of the locking wire. Instances have occurred in the case of Petro-Flex tubing where the looped portion of the armouring wire has broken off at the point where it issues through the sleeve. This loop serves the purposes of locking the end fitting and also of ensuring electrical continuity.
electrical continuity. When the looped portion is broken, it will, therefore, be necessary to fit a copper or brass clip to the sleeve of the end fitting and to attach the locking wire thereto. In cases where lengths of tubing exceed six feet, it will be necessary to fit additional metal clips which make electrical contact with the outer armouring wire, and which should be earthed to some portion of the aircraft in contact with the main "earth." In no case must the distance between bonding clips exceed six feet throughout the complete run of the tubing. This distance has been determined from a consideration of the highest frequency now being used for radio communication in
aircraft.
(v) When fitting Petro-Flex and Superflexit, particular care must be taken to avoid binding of the union nut and consequent twisting of the tubing, but graphite or other lubricant must not be used for this purpose. Where there is a bend in the tubing, the end adjacent to the bend must be tightened first. No attempt must be made to cure a leaky joint by turning the outer sleeve on the tubing or screwing the union piece further into the tubing.
HONG KONG,
6th December, 1937.
J. B. NEWILL, Director of Air Services.
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