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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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