Firesleeve or equivilant for thin tubing?

[claycookiemonster]

Laying out control cables forward of the firewall, and I blithely assumed I'd slip some firesleeve over one of cables that approached the exhaust pipes. Imagine my surprise to find that 1/2" ID was the smallest firesleeve available! My McFarlane control cables are 5/16" in OD. How do I protect them? There doesn't seem to be anything for such a small hose.

 

[TS Flightlines]

Might be able to help, Clay, I'll look tomorrow.
Tom

 

[erich weaver]

Heat shield on the exhaust will do the trick

 

[DanH]

Firesleeve tends to be overrated as an insulator.

Erich has the right idea...reflect as much thermal radiation as possible before it can reach the subject, sleeved or not. That means a good heat shield at the source (discussed previously) and a reflective surface on the cable sleeve.

 

[rmarshall234]

I just bought some 1/4” from Spruce. Search Black silicone firesleeve..

Where close to the exhaust, I then covered with alum tape.

 

[Reflex]

Clay, great question. I'm working on this very thing right now. I too am using McFarlane's cables. Couldn't find smaller insulation than 1/2". However, with the silicone boots that fit over the end of the cable, the 1/2" looks like it might be OK.

My plan is to use heat shields, insulate, wrap the insulation foil reflective tape, and then safety wire or clamp around the tape at the ends to help hold it in place.

If Tom comes up with better fitting insulation, that would be great.

 

[Freemasm]

Laying out control cables forward of the firewall, and I blithely assumed I'd slip some firesleeve over one of cables that approached the exhaust pipes. Imagine my surprise to find that 1/2" ID was the smallest firesleeve available! My McFarlane control cables are 5/16" in OD. How do I protect them? There doesn't seem to be anything for such a small hose.

Pegasus Auto Racing sells very quality products from my dealings so far. They sell firesleeve and have an aftermarket 5/16" size that I've utilized. Maybe not best the option for you here, but maybe another application for you.

 

[Pilot135pd]

I just went through this situation 2 days ago when I replaced one of those plain "push the botton" mixture cable with a vernier type. If I were doing it all new like you I'd look for something smaller but for my old plane I couldn't find a smaller firesleeve so I used the 1/2" I had laying in the shop and moved on to my other 1000 things to do.

 

[Desert Rat]

To make a smaller diameter firesleeve, you can split it longways then infuse the raw edges with red RTV. Once that dries, roll it up like a soft taco around whatever you're trying to sleeve, hold it in place with a twist of safety wire every couple of inches, then run a bead of red RTV down the seam.

The bonus is that if your cables are already installed you can do this without having to take anything apart.

I just went through this on my throttle cable, but I also installed a heat shield right below it that I made from stainless with a fiberfrax backing, per Dan Hortons excellent recommendation. In the picture below I want to say that sleeve started out as a -9 or something like that.

theres a thread on here from last month about that whole process titled home brew heat shield or something like that

 

[DanH]

Terry, might want to put a shield on the forward pipe too. I know it's just braided cable and tubing out there past the sheath nut, no plastic liner, but there will be conduction. In a perfect world, we want the assembly to conduct heat out along the cable length, not in. Energy always moves high to low.

 

[DanH]

Terry, might want to put a shield on the forward pipe too. I know it's just braided cable and tubing out there past the sheath nut, no plastic liner, but there will be conduction. In a perfect world, we want the assembly to conduct heat out along the cable length, not in. Energy always moves high to low.

Wrap the firesleeve above the pipe in shiny aluminum tape. It will reduce radiated energy absorption by a factor of roughly 10.

 

[wirejock]

Aluminum tape

Terry, might want to put a shield on the forward pipe too. I know it's just braided cable and tubing out there past the sheath nut, no plastic liner, but there will be conduction. In a perfect world, we want the assembly to conduct heat out along the cable length, not in. Energy always moves high to low.

Wrap the firesleeve above the pipe in shiny aluminum tape. It will reduce radiated energy absorption by a factor of roughly 10.

Wow! That's a lot. Do you recommend wrapping fuel and oil lines?

 

[DanH]

Wow! That's a lot. Do you recommend wrapping fuel and oil lines?

Are they near an exhaust pipe?

Serious answer, it depends. Think about it. Heat energy moves from high to low, by three mechanisms, conduction, radiation, and convection.

Most oil lines will be at 170 to 225 F. They are (hopefully) not laying against anything hot, so no conductive transfer. They are probably a long way from the exhaust pipes, as well as cylinder heads, so very limited radiant transfer. The engine compartment air around them, for most RVs, is about the same temperature as the oil. Significant high to low doesn't exist for any transfer mechanism.

Fuel lines are a different deal. Smart builders arrange components minimize line length in the engine compartment, and keep away it from hot stuff. Still, air temperature can be warmer (above 200F at times) than a desired max fuel temperature (less than 140F). High to low; energy moves from air to hose to fuel. So we insulate to slow that energy transfer, with an eye toward keeping the volatile components of the fuel below their vapor pressures...i.e. not form bubbles.

 

[David Paule]

Firesleeve tends to be overrated as an insulator....

A long time ago I had a fuel line with a heat problem, on a non-RV. I used firesleeve and that helped but wasn't quite enough. I added a second larger one over that and the problem went away.

Dave

 

[rmarshall234]

Terry, might want to put a shield on the forward pipe too. I know it's just braided cable and tubing out there past the sheath nut, no plastic liner, but there will be conduction. In a perfect world, we want the assembly to conduct heat out along the cable length, not in. Energy always moves high to low.

Wrap the firesleeve above the pipe in shiny aluminum tape. It will reduce radiated energy absorption by a factor of roughly 10.

Nice to have a rough number associated with the effect/improvement. The installation in the photo would make me really nervous, once had a throttle stick wide open because heat from the exhaust effected it.

 

[Desert Rat]

Interesting observations Dan. I guess I'd wonder- when is something good enough?

I think your suggestion to wrap in reflective aluminum tape is a good one and since I've got a roll on hand I'll likely go ahead on a do that. But, that roll of tape is also about $60 bucks. If I didn't already own it I'd probably take a pass unless a problem actually presented itself.

The heat shield below it is faced with aluminum tape on the hot side for max reflectivity and backed with a layer of 1/16" fiberfrax. I might eventually stick a thermocouple in there and see how hot it actually gets with what I have already.

Regarding the forward pipe; There's an inconveniently located ball joint right at that spot. If I install another heat shield there it's going to make it somewhat inconvenient to lube the joint with mouse milk per Vetterman's recommendation.

That leaves me questioning what I'm actually trying to solve for here. Originally, I was just trying to mitigate the known issue of heat degradation in the cable liner, so in the case of the fwd pipe is the juice really worth the squeeze?

I dunno, it's interesting to ponder stuff like this.

 

[Desert Rat]

Nice to have a rough number associated with the effect/improvement. The installation in the photo would make me really nervous, once had a throttle stick wide open because heat from the exhaust effected it.

I don't want a stuck throttle either, but what makes you nervous about this installation? I'm building an RV7, but the install I depicted is right out of the RV14 build manual, other than what I mentioned above (also excellent suggestions from Dan a month or so ago).

I'm not getting defensive at all, there's quite frequently a better way to do stuff, but I'm genuinely curious how else you think I could improve on this other that what's already been discussed...

 

[Bill Boyd]

Terry, so as not to discourage other frugal builders, there are rolls of 2" wide aluminum tape in the 4 mil x 50 yard range for under ten bucks all over Amazon; it's only slightly more at the local Ace Hardware, and is what I've used on my fuel lines anywhere near the exhaust pipes.

 

[rmarshall234]

what makes you nervous about this installation?

The critical nature of that cable and its extremely close proximity to a heat source. I’m looking at it with an inspectors eye and measuring it against best practices. I’m not going to redesign it or argue that Vans is doing it wrong, I’m only sharing my knowledge and experience - feel free to dismiss it.

 

[Desert Rat]

The critical nature of that cable and its extremely close proximity to a heat source. I’m looking at it with an inspectors eye and measuring it against best practices. I’m not going to redesign it or argue that Vans is doing it wrong, I’m only sharing my knowledge and experience - feel free to dismiss it.

I'm not dismissing your comments at all, I just wondered if there was something particular you saw that I didn't. When I saw how close this all stacked up it made me somewhat uncomfortable as well. However, there's lots of stuff that Vans does that "works" but is certainly not what we would consider a best practice. Making bushings out of soft aluminum tubing is another example that comes to mind.

Anyway, at this point, I don't know what I could do to make this better, except adding aluminum tape over the firesleeve as was suggested Other than that, It would require a complete overhaul of the system, and it's pretty hard to justify that with all the IO390s out there running this setup seemingly without issue.