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That's a great recommendation. The most common question we get is the difference between Teflon and Conductive Teflon. You can tell the difference based on the internal color of the hose. However, we have seen some manufacturers of imported non conductive hose color it the same as conductive. That's why it's important to buy from a supplier you trust. The more questions that you ask of vendors/suppliers, the better informed you can be about the decisions you make. On the outside, stainless braided hoses all visually look about the same. What's inside is what counts. The same thing is true with fittings.... Crimp versus Reusable, Swivel or not, Material (whether its actually a certain material or just a plated coating), and thread type are all things to look into when deciding what to put on your aircraft. As has been mentioned many times, if you use high quality materials and they are assembled properly, you should have a long lasting assembly. |
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The "at home" safe process is to fill the hose with fluid, for the quickest pressure relief, and then use a "Compressed Air Flow Safety Shut Off Valve" on the inlet to the test kit (search on that...about $30 device). One should probably have this handy device to prevent "whip lines" on a compressed air system anyway. I use water, also in the water filled bucket, so if there is a failure the pressure relieves quickly. In the spirit of actually experimenting...I purposely partially assembled a fitting with only slight compression on a test hose. At 150 psi, the fitting did finally come off after waiting about 10 minutes, but it was a "pop" and that was it. My take-away was that the Earl's Speed Seal system is a pretty solid design. And yes, I agree, the whole process should be about the "experience of building". I personally enjoy doing the whole thing, from the big things like the airframe and engine, down to hoses and servos - all the way down to those little HD pins on the Garmin D-sub connectors. It's all part of the process of recreation and education. Bob Noffs: not sure if you were being serious or not, but just in case... here's the link for AN8 hoses. Pick your ends and length... AN Plumbing AN8 pre-made hoses |
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Also: Since this topic is really interesting. How does ONE satisfy the "condition" of a Teflon SS braided hose? I mean lets say every year you look at them and from the outside they look the same. I assume this is the reason Cert. hose just get replaced every X years to be sure? What is the proper method to determine when the hose need to be replaced? |
Lets compare apples to apples----conductive hoses verses non conductive. Aluminum nuts, and brass collars, and probably brass stems, verses 304 stainless steel fittings and stainless collars. GRANTED---- some guys are shopping to get the lowest possible costs available. Some like the whole process of building their own hoses, engines, avionics, etc. Absolutely nothing wrong with that in my view. Actually we welcome it in alot of cases. BUT---we've found that the majority of builders dont want to do those jobs. They want to do the install, and move on. So there are vendors that specialize in such things as hoses and fluidlines, engines, avionics and wiring harnesses, fuel tanks, and yes even building the airframe.
WE set out to fill that void----and its not for everyone. We are NOT the cheapest, nor the most expensive, and dont want to be either. We have MANY friends on VAF that have never bought anything. Yes we are still friends, and talk to them as if they spent a bunch of money. Its about people, and products and offering what we have and can do. Tom |
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Ron, If you're using the Speed Seal system with Speedflex Conductive Telfon hose and Stainless hose ends, it is a very solid system. That is the one we recommend to customers who want to do it themselves. You won't save any money by going that route, but you will be able to say that you built all your own hoses. I agree with you.....this stuff is fun and some people thoroughly enjoy it. Others don't. If you are filling your hose up with fluid ahead of time it is a hydrostatic test, which is the correct way of doing it. You don't have a method to purge the air from the line before testing but with a 150psi test it won't much matter. The video of the test showing how to use their equipment does not show a hydrostatic test, but rather just filling the line with compressed air. That is a good way to turn an improperly attached fitting into a projectile. The link to the AN8 pre-made hoses is something completely different. We could absolutely build hoses with those components and sell them at that price, but we choose not to for a wide variety of reasons. There are places to save money, but I can tell that you are a person that is concerned with quality. If you weren't, you wouldn't be utilizing Speedflex hose and Stainless Ends. As Tom mentioned, we have both spent hours talking to builders who never buy a thing from us. Ultimately, we want to see safe airplanes being built. Experimental aviation is a community with the opportunity to make lifelong friends. Quote:
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Do I think that the typical RV owner doing his own maintenance will do that pressure testing...probably not. |
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When you test a hose to proof pressure you ensure that the end fittings are secured to a level that will preclude the possibility of the fittings failing under normal levels of vibration and flexing. Testing the hose to 150 psi does not provide that security. All you're doing is satisfying yourself that the actual operating pressure of the hose will not push the end fitting off....but it's not the actual operating pressure on fuel lines that represents the real threat....it's the vibration and movement of the flexible hose into the fixed end fitting. |
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Now, flying airplanes, let alone building them, is perceived by many as dangerous as well, so based on that, I suppose I have to agree with you that building, testing and using your own hoses is also dangerous. But then again, according to the CDC, two thirds of all injuries happen in the bathtub or shower, so I should probably avoid those too. ;) |
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The link is to pre-made hoses constructed of Earl’s Speed-Seal braided hose with aluminum fittings, both crimped and pressure tested - to the same pressures I believe you stated. Perfectly adequate for the installation. And if you’re saying that only steel or stainless steel fittings can be used, then Beechcraft needs to have their type certificates pulled as nearly every fitting on my Baron is a ‘D’ fitting (aluminum). The only steel ones in the IPC called for are on the lower brake hose that connect to the caliper. |
The Mil Spec for H8794 hose ends from -3 to -6 use steel nipples and nuts, with aluminum collars. -8 and above use all aluminum fittings. These are the resuables for 303/111 type hose. 'MOST' Certified teflon assemblies will use stainless or CRES hose ends, at least up to -8.
In answer to the question on testing a teflon hose after its been in service, it get alittle complicated. Mot teflon hoses will take a set through temperature and pressure cycles, making it conform to its installation routing. So if the routing has a curve in it, the hose after extended use may stay in that curved pattern. Removing the hose for reinstallation requires supporting the hose so it maintains the installed shape. Dont try and straighten it out, then reinstall it because the liner may fracture and leak. For the same scenario, trying to pressure test a teflon hose that has taken a set, is an issue especially if you try and go to the proof test pressure . The hose will naturally want to straighten out and may fracture the liner. So, most long time inservice teflon hoses are replaced. What that interval is is dependent on the application, the temps and pressures involved, and the amount of movement the accessories have. Obviously, hoses that move under higher pressures like on retract landing gear should be inspected and replaced at high cycles. For our purposes, most teflon hoses have no service life. When it gets down to it, the aircraft manufacturer can specify what goes on the aircraft. In Rons case, Beechcraft specified that aluminum hose ends be used, or a Mil Spec equivelant with aluminum hose ends. In the experimental world, the kit manufacturer can specify what to use, but its generally up to the builder to use the specified parts. As we all know---some do, some dont, some opt for quality reliable assemblies from well known sources, some, well lets just say we've seen some pics of hose assemblies that really makes you wonder. Tom |
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1. Speed Flex hose and Speed Seal Reusable fittings are high quality and come in Aluminum, Steel and Stainless. Certified hose manufacturers typically use SS or CRES for -8 and smaller size hose. On our pre made assemblies we choose to utilize stainless on our -8 and smaller assemblies for quality and longevity even though it is more expensive than aluminum. For -10 and larger size fittings we utilize Aluminum hose ends. This creates a pricing structure that is very similar to the cost of a high quality do it yourself hose. 2. There is nothing wrong with Beech utilizing aluminum fittings. Every manufacturer has the leeway to specify what their engineers feel is adequate for the job. The Baron is a great plane. We utilize aluminum fittings also in our larger size hoses because it is the most appropriate material for the application. 3. Pressure testing to 150PSI is a good leak check. It is not a good "proof" test. There is a difference. With that said, mechanics have assembled 303 hoses for years with the only leak check being a functional check once it is installed on the aircraft. 4. Like many manufacturers, Earls has a variety of different products at differing qualities for different applications. The link provided for pre-made hoses is not the same quality of components as some other products that Earls offers. It is a low cost option. As such, the components are manufactured differently. |
I have always enjoyed assembling 303 hoses, new or replacements, using the official assembly mandrels and proper assembly lube. Then followed by the old compressed air blow through test to check for a rubber "flapper" blockage. Never pressure tested.
I had a staInless braided fuel line on my Nanchang leak like a soaker hose just like the video linked to in previous post here. But worse. Ugly. The previous owner had assembled his own hose from hotrod supplies. The hose looked great on visual inspection but was a pasta collander pouring out fuel the full length. A contributing factor was the aircraft used metric fittings with non-standard flare angles which gravitated one towards the hotrod and industrial hose side. This fuel leak was scary stuff and I decided then and there that I wouldn't use any of the stainless braided fuel hose or shiny faux AN fittings from automotive suppliers. The fittings may be the proper dimensions and flare angles to match AN sizes but some appear to be cast prior to cleanup and anodizing. And there is no mention of alloys used. I still make my own 303 hoses if I am reusing end fittings, but have switched over to TS Flightlines for new assemblies. I just did the firewall forward on my RV-8 and mailed the old hoses to Tim and company for replacement. I am very satisfied with the quality and fit. A side benefit is they are asethically pleasing to look at. If I were doing a pre-purchase inspection on an RV with these hoses in my opinion I would expect it to enhance the resale. I do have a bit of pause based on the Teflon taking a set over time and the potential for an unitiated owner and/or mechanic to flex or crack the Teflon lining if inspecting the hose the same way they have traditionally done with rubber. Jim |
Jim---need metric hose ends for your Nanchang? Well this isnt RV related, except the fact that Vans uses a Rotax in the RV12s, and it does in some cases use metric fittings. SO maybe the moderators will give me alittle leeway here.
One of my pet projects was to design hose ends for both teflon and H8794 (303/111 common hose) in aviation metric. Believe it or not, its NOT the same as the industrial versions we see on a regular basis. YEP---minor differences in the ball head, but its enough to have a potential issue. Because of our work with Rotax and a few European Warbirds, Steve and I decided to work on a metric set of hose ends to fill the void. Long story short, lots of research and samples back and forth from Germany, pictures and specifications from the Smithsonian, and some OE metric hose ends from Rotax, we have designed metric DIN hose ends for teflon hose. Have a few prototype samples under lock and key with an armed guard. Dont have them all other than drawings done, but we started with -8, (18mm) because it was common to Rotax and their European oil tank. WE 'may' produce these in volume, IF we can justify the expense by sales volume. OH----the other thing I was going to do--is produce the hose ends in a reusable version for modern H8794 hose thats common around the world. With everything going on-I put that away for a while. OH---if someone has a 'special' situation (dont know why) and needs a 'creative hose end' solution, let us know. Tom |
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This is what Tom Swearengen of TS Flightlines has to say on the topic: "Pressure testing....slightly more involved than just a leak check at 120psi under water. You want to take it to the rated working pressure OF THE HOSE, then a safety margin." And this is what Steve Tschurwald of Aircraft Speciality has to say: "Regarding pressure testing...a 150psi pressure test will give peace of mind, but will not serve as a proof test for the fittings. We could crimp a hose that would hold at 150psi that would fail over time under under normal operating pressures and vibration." Now maybe these people who are actually making a living out of fabricating aviation hoses might just know a thing or two. Personally it doesn't worry me one bit if you do not want to utilize aviation best practice in pressure testing your home-made hoses, but it does worry me that you might encourage other builders on VansAirforce to adopt a fundamentally unsafe practice. |
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I think TS Flightlines and others in the hose business are providing a very useful service and a high quality product, but I (and presumably others) have used them out of convenience, rather than because of demonstrated safety concerns over DIY hoses. |
I have built all sorts of hoses and have a pressure test setup I fabricated with an old bottle jack and pressure gauge. You'd almost have to be brain dead to misassemble an Aeroquip 303 hose and 491 fittings. The majority of certified aircraft fly with 303 hose so its nice to stock just a few sizes of hose and reuse the fittings. New 303 hoses are very flexible and I believe these hoses transmit the least vibration to the airframe for fuel and oil lines connected to the firewall or engine mount, when compared to stainless braided lines. I have used stainless braided lines on my airplanes but they're heavier and overkill.
A few weeks back I found a truck air brake line lurking under some firesleeve for the fuel line on a Cherokee 6. That got replaced with 303 in a heartbeat. |
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You're absolutely right that a lot of certified aircraft utilize 303 hose. A lot are starting to migrate to Teflon as the standard on many new installations now also. https://www.lycoming.com/content/engine-hoses "Lycoming has phased in Teflon hoses with silicone-coated fire sleeves. These are the only hoses which are available for field replacement, and they will be found on engines shipped from the factory." - Quote from link above. 303 is an ok hose and was the standard for a long time....but it is definitely NOT lighter than stainless braided teflon hose. a -6 303 hose has a weight of .228lbs/foot. Conductive Teflon hose is slightly less than half that weight and a lot less bulky. The minimum bend radius on 303-6 and the conductive Teflon -6 hose we use is the same at 4". The OD of the Teflon hose is less than .45" whereas the 303 hose is .672. That is due to the much thicker wall on the 303 hose. Again, there is nothing wrong with 303 hose, but it is heavier and bulkier than conductive Teflon with a much shorter life. A truck air brake line huh? I'll add that one to the list of interesting stories we have heard. :) Sadly it's not anywhere near the craziest. |
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What concerns me is that there are people, based on the statement above, who clearly do not understand the engineering involved and create an environment of fear, uncertainty and doubt within a community where education, knowledge sharing and encouragement should be the hallmark. I have no issue with being called defensive - I am defensive against misinformation, group thinking and the "it's what we've always done" mentality. It's apparent that there are many people who prefer not making their own hoses and many who want to do it themselves - with drivers being everything from tooling, skill, money, time, fear, and many more I'm sure... (the basis for my statement previously regarding "never ending debate"). But rather than tell folks NOT to do it themselves and dissuading people, instead, let's pursue the design parameters, performance requirements and processes to let people decide how to proceed without impugning their decisions. |
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