Aircraft Hoses

Aircraft Hoses

Khagendra kumar yadavM-tech (AME)Hindustan University

contentHose-Introduction

HOSES :SERVICE LIVES

Hose Materials and Construction

Hose Identification

Storage of hose

Hose installation

Hose

A multiple-layered flexible conduit through which fluid is conveyed from one point to another.

Flexible hose is used in aircraft fluid systems to connect moving parts with stationary parts in locations subject to vibration or where a great amount of flexibility is needed. It can also serve as a connector in metal tubing systems.

The hoses have been classified in two groups :

GROUP A : Fuel, Oil, pneumatic and hydraulic pressure

hoses.

GROUP B : All other hoses like hydraulic return line

and instruments hoses etc.

HOSES :SERVICE LIVESShelf Life :

The total storage/shelf life of both types of hoses shall be limited to 10 years from the cure date of manufacture.

During storage, periodic inspection should be carried out once a year for signs of deterioration, weather cracks, signs of corrosion on end fittings etc. and hose pressure tested to 1-1/2 times the working pressure every two years.

Before installation on aircraft pressure test should be carried out at 1-1/2 times the working pressure.

Service Life :

Group A hoses – max. 4 years extendable upto 6 years

Group B hoses – max. 6 year extendable upto 8 years

Hose Materials and ConstructionThe two basic hose materials are synthetic rubber and

polytetrafluoroethylene (PTFE).

To meet the requirements of strength, durability, and workability, among other factors, synthetics are used in place of pure rubber. Synthetic materials most commonly used in the manufacture of flexible hose are Buna-N, neoprene, butyl, ethylene propylene diene rubber (EPDM) and Teflon™.

One material which is widely used for the manufacture of hose for engine and hydraulic systems is polytetrafluoroethylene (PTFE). This material is chemically inert, is unaffected by the synthetic oils and fluids used in aircraft systems, operates satisfactorily at high fluid and ambient temperature and normally has an unlimited shelf life.

Low, Medium, and High Pressure Hoses

Low pressure — below 250 psi. Fabric braid reinforcement.


Used for instruments mounted on panels equipped with vibration isolators and the rudder.

Medium pressure — up to 3,000 psi. One wire braid reinforcement. Smaller sizes carry upto 3,000 psi. Larger sizes carry pressure up to 1,500 psi.


High pressure — all sizes up to 3,000 psi operating pressures.


High pressure hose assembly

• Consist of an Inner tube or lining covered by one or two closely woven wire braids, either moulded or sandwiched between the synthetic rubber of the tube or woven on the surface of the tube.

• The whole may be enclosed by an outer cover, the purpose is to protect the other parts of the hose, to resist abrasion and the effects of weather and in some case, to provide a degree of fire resistance.

Hose IdentificationSynthetic rubber hoses with rubber covers are

identified with the military specification number, the size by dash number, the quarter and year of cure or manufacture, and the manufacturer’s code identification number or federal supply code number printed along their layline(fig A). The layline is a legible marking parallel to the longitudinal axis of a hose used in determining the straightness or lay of the hose.

Synthetic rubber hoses with wire braid cover are identified by bands (fig B)wrapped around the hose ends and at intervals along the length of the hose.

Hose Identification

MIL-H-8794-10 3/71 (06827)

Hose Identification

Sizing

The size of a flexible hose is identified by the dash (-)number, which is the ID of the hose expressed in 16ths of an inch. For example, the ID of a -64 hose is 4 inches. For a few hose styles this is the nominal and not the true ID.

Cure Date

Synthetic rubber hoses will deteriorate from aging. A cure date is used to ensure that they do not deteriorate beyond material and performance specifications. The cure date is the quarter and year the hose was manufactured. For example, 1/89 means the hose was made during the first quarter (1 Jan to 31 Mar) of 1989. The cure date limits the length of time a rubber hose can be stored, in bulk or as an assembly, prior to being placed into service. The storage or shelf life for rubber hose is 4 years. For the hose manufactured in 1/89, the storage or shelf life will end on the 31st of March 1993.

Hose Identification

Storage of hoseAircraft hoses and hose assemblies should be stored uncoiled and supported so as to release stresses.

Temperature : The storage temperature should be between 50 deg. F and 70 deg. F and the distance between the stored articles and the source of heat should be more than 3 feet.

Humidity : The relative humidity in the store room should be around 65 percent.

Light : Rubber parts should not be exposed to strong light e.g. direct rays of sun. The store rooms should be kept as dark as practicable.

Hose installationMachine Tolerance

Hose assemblies must not be installed in a manner that will cause a mechanical load on the hose.

Provide slack or bend in the hose line to provide for changes in length that will occur when pressure is applied.

Motion Absorption

Provide additional bend radius when lines are subject to flexing and remember that the metal end fittings are not flexible. Place line support clamps so as not to restrict hose flexing.

Hose installation

Twisting

Observe linear stripe. The hose must not be twisted. High pressures applied to a twisted hose may cause failure or loosen the nut.

Hose installation

Minimum Bend Radius

Hose rupture or leakage may result from bending too close to the hose/fitting connection.

Hose installation

Hose Strain

Relieve sharp bends, avoid strain or hose collapse, and make cleaner installations by using Aeroquip elbows or other adapter fittings. Provide as large a bend radius as possible. Never use less than the recommended minimum bend radius specified for the hose.

Hose installation

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Aircraft Hoses