Frequently Asked Questions about hose assemblies
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PTFE hose assemblies are able to replace rubber in several 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 many 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 as 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 with your inspector before changing the hose assemblies.
Not only the working pressure is necessary for the correct choice 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 type certificate holder. If the IPC (Illustrated Parts Catalogue) does not show a PTFE hose assembly, it is not authorized and shall not installed. If the TC-holder of the aircraft is no longer active, the responsible department from the EASA should be contacted.
NOTE
An inspector assist in regards to this question, but he is not allowed to authorize the use of PTFE.
Can rubber hose lines be replaced by Teflon® hose lines?
When do PTFE aircraft hose assemblies need to be exchanged?
This decision is made by the type certificate holder. The common 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.
This decision has to be made also by the type certificate holder.
NOTE
Some people think the life cycle intervals (life limits) are only made for aircraft. This is wrong. Rubber hose assemblies age too! Hose assemblies do age not only by light, they also age by air or the used medium. Other industrial sectors are also affected. The demand of life limits is a general demand.
When do rubber aircraft hoses need to be exchanged?
When does a hose assembly need fire protection?
According to EASAs CS23.1183 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.
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.
Should a hose assembly be new, or would an overhaul of the old hose assembly be more economical?
Do you supply complete sets of hoses in advance – so-called kits? The expenditure for the renewal of the hoses could be lowered thereby.
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 original data. Of course there are some aircraft that make it look possible to sell kits, 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 same kind make this opportunity uneconomical.
YES, if the aircrafts hose assemblies were made in the past by WMT.
It’s not an issue to find information about hose assemblies that were 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.
The first decision is yours!
If you send us your order early enough, we are able to deliver within 2-4 days.
How long does the overhaul of hose assemblies last?
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 online or printed order form. That will save time because we don’t need to wait for the sample hoses. Also, there is the benefit of saving in shipping costs.
You can find all relevant information on the Certificates Website (Hose assemblies>>Certificates)
https://www.wmtonline.eu/en/products/hose-assemblies/certificates/
