Rubber hose life? Silicone hoses?

"Sean, do you recall if the "two year" grace period before the five year clock starts appears in any of the Rotax documentation?  I searched through the Line Maintenance Manual but only saw the "five year" period mentioned."

I researched this when putting my Sonex into the air with a  brand new (4 years since purchase)  912ULS. I was either told by my local Rtrax agent or saw it written (in this Forum?).

Homebuilder misjudging the time to engine install/start  is such a common problem, Rotax has responded to by advising a "grace " period before the clock starts. Have you checked your engine warranty document - might be there.

One of the Forums gurus will known the answer for sure.

Dear Michael,

when I had a new engine installed by an aviation company (2022), all the rubber hoses were of course replaced.
However, some silicone hoses (water) were not because they were hard to obtain and the old ones were still good. They were soft and were fine on the outside.
The previous engine had old hoses, e.g. the fuel line. The previous owner said: "They'll last a few more years". And that's how it was (I wouldn't trust that today)!
How old were the hoses on my old plane (the plane was in continuous operation)?
I don't know exactly, but according to the repair records and the delivery bills for the spare parts, it can be assumed that some of the rubber hoses were at least 10-15 years old and older, and the silicone hoses were no younger.
A car is not an airplane. But the hoses installed in the car don't know that. It is unreasonable to drive a car until it stops. Even with a car, you decide how the hoses look (flexible) and if not, then they are replaced. I don't know of any fixed rules as to after which years the hoses in a car are replaced.

What do we learn from this?

1. The hoses, whether rubber or silicone, usually last much longer than ROTAX specifies (with standard industrial quality - this cannot always be said for China quality)

2. The ROTAX tension clamps or the tension clamps in general can only build up a certain amount of tension due to their design. If the tube and hose do not fit together exactly, e.g. if the hose is slightly larger or high pressures are to be expected, then the clamps are useless. When I work on a hose, I replace each clamp with a screw clamp.

3. if the engine has/need a Form 1 (EASA) or the engine must be certified (I don't know the rules in the US) then you don't need to think. ROTAX and the state authorities have done the thinking for you. Replace all hoses and document every hose. Practical experience: At home, a historic airplane was grounded because the hoses were only in operation for 5 hours but the 5-year deadline had expired. Nonsense to the power of 3 - the hoses are in new condition - I inspected them myself - costs approx. 10,000 €.

4 - If you have the freedom to decide for yourself (here in Germany if you have a Microlight) then you can think for yourself. Let common sense have its say.

5. if you are an Aviation company or you are working on an engine for others then you are not allowed to think for yourself. Do it the way ROTAX or other authorities prescribe.

Nobody can tell you how long hoses will last. That depends on many factors. Materials that change in composition during operation or simply due to age are of course subject to an ageing / annual limit. However, this should hardly be the case with high-quality materials. However, since nobody can look inside the materials, I fully understand if ROTAX specifies such replacement rules. If you ask in a ROTAX forum, what answer do you expect?

Greetings

Hi HKK

"2. The ROTAX tension clamps or the tension clamps in general can only build up a certain amount of tension due to their design. If the tube and hose do not fit together exactly, e.g. if the hose is slightly larger or high pressures are to be expected, then the clamps are useless. When I work on a hose, I replace each clamp with a screw clamp."

I do not agree with this advice

"If the tube and hose do not fit together exactly," Do not use hose/tube that does not have the correct ID, to suit the spigot/barb OD. A slightly small ID hose can be used but never a larger ID.

Correctly specified hose,  push fitted onto a  proper spigot/barb, should not require pressure from a hose clamp to seal them.

Clamps are for security (preventing the hose slipping off) not for leak prevention.

The automotive world has moved to constant tension spring (CTS) clamps for most hose fittings.

Rotax have moved to CTS clamps for all coolant hoses.

CTS clamps are less likly to cause damage to the hose and are more than adequate to secure the hose in place.

I use fuel injection clamps on my oil & fuel lines. They come in various designs however all feature smooth edges and some method to prevent damage to the tube ie 360 degree pressure and a protective inner sleeve.

We change hose and do preventive maint. because like a car we can't pull over to the curb and you may be flying over some nasty territory. Remember an ounce of prevention is worth a pound of cure. OR I don't want to injure or kill myself or my passengers OR pay thousands of dollars to fix something that didn't have to happen. 

When a use a screw on clamp I use the fuel injection clamp pictured to the left in the Sean's last post. I NEVER use serrated worm drive clamps. That's just old outdated tradition and a failure to be more progressive. I use Oetiker clamps for fuel, fuel injection clamps for oil hose and if I use a worm drive clamp on a 25mm (1") coolant hose then I use a Wurth Zebra clamp. It has raised rips and does a far better job in sealing in a good 360 degree clamp pressure and it doesn't cut into the hose or strip out and come loose.

The number one problem I have found during a hose change is way too many people over clamp the hose which cuts into the inner liner. So when someone says I can look at a hose and tell it's okay that must mean they took all their hoses off and out of the fire sleeve and unclamped them to look at the inner liner because the outer shell and middle of a hose usually isn't the problem. I have pictures of these cut up hoses on the inside where they were over clamped.

Hi Roger/HKK,

I use constant tension spring clamps, like the one shown, on all my coolant hoses.

I love them! - Quick and easy to install/remove (with the correct tool), light weight, 360 degree constant pressure, secure, can not be under/over tightened (so no damage to the hose) and can be reused multiple times (how many 5 year intervals are we expecting?).

Thes clamps have been used, in the automotive world, for at least the last 15 -20 years - no leaks. Rotax has, in recent times, supplied new engines with this style of clamp on the coolant hoses.

If you go down this route, be very careful with selecting the correct size for the OD of the hose, you want to clamp😈