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Frequently Asked Questions about hose assemblies

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1.Can rubber hose lines be replaced by Teflon® hose lines?

PTFE hose assemblies are able to replace rubber in a lot of cases. For example if you use regular gasoline from a gas station PTFE would be the better choice for fuel hoses.
PTFE hose assemblies do have much advantages, but they are not the "non plus ultra".The usual PTFE hose for aircraft use is made of an inner tube (PTFE) and a steel wire braid for taking the pressure. PTFE hoses regularly do have a worse bend radius than rubber hoses and they are not that flexible. High frequencies are able to force the PTFE to flow. As a result the inner tube can start to be porous. Please look into the technical data related to your aircraft and speak to your inspector before changing your hose assemblies.

Not only the working pressure is necessary for the correct choose of the PTFE hose assembly, also other features like the bind radius for high pressure PTFE hoses is important. Please refer to the online Stratoflex product catalogues.

The authorization for choosing a PTFE hose assembly instead of a rubber hose assembly is given by the aircraft manufacturer. If the IPC (Illustrated Parts Catalogue) doesn’t show a PTFE hose assembly, it is not authorized and shouldn’t be built in. For aircrafts that do not have any manufacturer left, the responsible from the EASA should be contacted.
NOTE
An inspector is able to assist you regarding this question, but he is not allowed to authorize the use of PTFE.

2.When do PTFE aircraft hose assemblies need to be exchanged?

This decision is made by the aircraft manufacturer. The commonly meaning of an unlimited service time for this hose assemblies is not true. Some manufactures define the lifetime of PTFE hose assemblies with “On Condition”. On Condition is an unclear meaning that leaves a lot of space for interpretation. The responsibility should go over to the owner and the inspector. Meant is the control of built in hose assemblies that are untouched.

This way hose assemblies can only be inspected by their surface, they cannot be inspected properly without being detached. The German Luftfahrtbundesamt handles general statements like on condition by saying: if nobody defines “on condition”, the hose assemblies have usual overhaul intervals.

Usually all hose assemblies are renewed when changing the engine. Also PTFE hose assemblies. PTFE hose assemblies can become dimensionally stable by ageing and high temperature. By disassembling them, the inner tube can be deformed or corrupted. The risk is increasing with the radius of the hoses. Hose assemblies with an inner tube bigger that ½” tend to kink very easily.

3.When do rubber aircraft hoses need to be exchanged?

Even this decision is made by the aircraft manufacturer.
NOTE
Some people think the life cycle intervals (life limits) are only made for aircrafts. This is wrong. Rubber hose assemblies are ageing! Hose assemblies are ageing not only by light, they are also ageing by air or the used medium. Other industrial sectors are also affected. The demand of life limits is a general demand.

4.When does a hose assy need fire protection?

According to JAR 23.1183 all hose assemblies that are exposed to flammable liquids or carry gas or air should be at least fire resistant.
We recommend to put a fire sleeve on every hose assembly that is in front of the fire wall.

5.Should a hose assembly be new, or would an overhaul of the old hose assembly be inexpensive?

PTFE hose assemblies are usually made with pressed fittings. Pressed hose assemblies can’t be disassembled or overhauled.

Rubber hose assemblies are usually made with screwed fittings (reusable). They can be disassembled and the fittings can be reused.
For the most common hoses with straight fittings a use of the old ones is likely the same like taking new fittings. The expense for the disassembling, the cleaning and the check of the old fittings is most times not worthwhile. As a Distributor for Parker Stratoflex – we are buying directly from the manufacturer – we are able to offer a competitive price for our new hose assemblies.
Hose assemblies with elbow fittings are less expensive if the old fittings are used again. Hose assemblies overhauled by WMT are comparable to new made hose assemblies.

6.Do you supply complete sets of hoses in advance - so-called kits? The expenditure for the renewal of the hoses could be lowered thereby.

YES, if the aircrafts hose assemblies were made in the past by WMT.
It’s not a big deal for us to gather information about hose assemblies that we made in the past. Since 1995 all information about assembled hoses is kept in our database. Because all of our hose assemblies are unique all we need to know is the serial number of the hose assembly. You can get it from the second row of the hose label. For example: SL98-230-5 The logic behind this number is SL for hose assembly (Schlauchleitung), 98 for the manufacturing year, 230 is the work order and -5 is the 5th hose of this order.

NO, if we are talking about a first time order.
If we don’t have data about an aircraft, we are not able to build the hose assemblies without receiving the originals. Of course there are some kinds of planes, that make it look possible to sell kids, but the practical work disproved it. Later made changes also within the same model range show new hose assemblies with different length or fittings. Only one wrong delivered hose assembly could result in a relevant delay of the airworthiness of aircraft. Life limits for rubber hoses and a small disposal for hoses of the same kind make this opportunity uneconomical.

7.How long does the overhaul of hose assemblies last?

First of all you are deciding it!
If you send us your order early enough, we are able to deliver within one working day. Depending on the amount of work it could take up to two working days.

If you send us an express package, we are going to handle it like express. If you send it by common post, we handle it with a lead time of mostly two days, that means that we handle express preferred but still work with an acceptable lead time.

8.Can I help shorten the delivery time?

Yes. If you measure your hose assemblies on your own by using our online assistance (Hose Assemblies >> Ordering) and fill out our printed order form. That will save time because we don’t have to wait for the sample hoses. Orders made this way can mostly go out on the same day if we receive them until 11am. On top you can save on your side shipping costs.