Van's Air Force
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Aeroquip VA-134 Oil Cooler Hose Service Life
- Thread starter dekagram
- Start date
I Think this old AC has been superseeded, but AC20-7N spelled it out. It mainly applied to H8794 hose (Aeroquip 303, Stratoflex 111 and others). Teflon is considered non-life limited under normal operating conditions.
Tom
Tom
I would like to add this:
While this old AC serves as a guideline that we've used for years, we know that many have not. And not just in experimentals (where there ISNT an actual criteria, but does have acceptable standards taken from GA aircraft), but in GA aircraft as well. We've seen many hoses that had date codes more than 20 years old that finally were taken off aircraft. Looked ok visually, until you did the 'Rice Krispies" test---you know that snap, crackle, and pop sound of the rusted steel (not stainless) braid breaking under the the cotton outer cover. Liners cracked both externally and internally, and honestly was a failure that was waiting to happen.
What is even more puzzleing to me is that very few wing supply hoses on GA aircraft get changed. Same deal, although they arent under pressure only suction, but fuels still flow through them. I've seen some on planes built in the 70's where the tank hoses were the originals. So 45-50 years +- of fuel, with different additives over the years that have affected the hose liners, and they dont warrant replacement? And--supposedly the planes go through an annual inspection AND sign off?
We've taken the position (some agree, some dont) that 8 years in service for rubber lined hoses and they should be replaced. I personally think that AC20-7N was set up for planes that flew ALOT, thus their replacement cycle of 5 years or at engine overhaul whichever came first. 400 hours average per year based on a 2000hr TBO is alot of flying. I dont know of many experimentals flying that much per year ---maybe some are. But, I say most have replaced theirs with teflon anyway, and the normal service life replacement time goes away, but still inspect them. Just did some that had 2006 date codes.
Since there wasnt a guideline for experimentals, we adopted the position of the GA industry. We took it a step further and were proactive in using teflon assemblies to provide a arguably safer, more cost effective alternative for hose assemblies. Lets face it, changing hoses every 5-8 years can get expensive, and even upgrading to teflon can be expensive too, generally 1 time. Some builders do their own from 'race car' products. Nothing against that, except that EVERY race car hose manufacturer (Specifically Earls and Russell) have disclaimers about using their products on any aircraft. When you purchase these products from the online race car parts stores, they dont know what youre putting them on.
The other option was to use certified assemblies, either H8794 (303/111 hose) or teflon, with the higher cost involved, and supposedly the service life replacement criteria. Rotax has/had a 5 year replacement cycle on its rubber assemblies, and a has changed alot of them to teflon. We've been advocating the use of teflon assemblies for years, not because its cool or sexy, but because of the safety and performance advantages. Of course, that is an arguable point, that I wont go into here.
So in answer to Greg's question, experimentals dont have a set criteria, but use accepted standards, and that would be 5 years in service for rubber lined hoses per AC20-7N.
Tom
While this old AC serves as a guideline that we've used for years, we know that many have not. And not just in experimentals (where there ISNT an actual criteria, but does have acceptable standards taken from GA aircraft), but in GA aircraft as well. We've seen many hoses that had date codes more than 20 years old that finally were taken off aircraft. Looked ok visually, until you did the 'Rice Krispies" test---you know that snap, crackle, and pop sound of the rusted steel (not stainless) braid breaking under the the cotton outer cover. Liners cracked both externally and internally, and honestly was a failure that was waiting to happen.
What is even more puzzleing to me is that very few wing supply hoses on GA aircraft get changed. Same deal, although they arent under pressure only suction, but fuels still flow through them. I've seen some on planes built in the 70's where the tank hoses were the originals. So 45-50 years +- of fuel, with different additives over the years that have affected the hose liners, and they dont warrant replacement? And--supposedly the planes go through an annual inspection AND sign off?
We've taken the position (some agree, some dont) that 8 years in service for rubber lined hoses and they should be replaced. I personally think that AC20-7N was set up for planes that flew ALOT, thus their replacement cycle of 5 years or at engine overhaul whichever came first. 400 hours average per year based on a 2000hr TBO is alot of flying. I dont know of many experimentals flying that much per year ---maybe some are. But, I say most have replaced theirs with teflon anyway, and the normal service life replacement time goes away, but still inspect them. Just did some that had 2006 date codes.
Since there wasnt a guideline for experimentals, we adopted the position of the GA industry. We took it a step further and were proactive in using teflon assemblies to provide a arguably safer, more cost effective alternative for hose assemblies. Lets face it, changing hoses every 5-8 years can get expensive, and even upgrading to teflon can be expensive too, generally 1 time. Some builders do their own from 'race car' products. Nothing against that, except that EVERY race car hose manufacturer (Specifically Earls and Russell) have disclaimers about using their products on any aircraft. When you purchase these products from the online race car parts stores, they dont know what youre putting them on.
The other option was to use certified assemblies, either H8794 (303/111 hose) or teflon, with the higher cost involved, and supposedly the service life replacement criteria. Rotax has/had a 5 year replacement cycle on its rubber assemblies, and a has changed alot of them to teflon. We've been advocating the use of teflon assemblies for years, not because its cool or sexy, but because of the safety and performance advantages. Of course, that is an arguable point, that I wont go into here.
So in answer to Greg's question, experimentals dont have a set criteria, but use accepted standards, and that would be 5 years in service for rubber lined hoses per AC20-7N.
Tom
