CREDIT TO “ROD”:
My understanding is that all rubber hoses are to be replaced every five years unless they are the Teflon type (Teflon hoses). If they are still real pliable, and have no signs of cracking, and are out of the weather, can that five years legally be extended to another couple of years (shelf life versus service life)? A friend of mine changed out all his engine hoses to Teflon type, I believe; do they make them for the gear too?
Search strings: Hose replacement, new hoses, oil lines, fuel lines, replace my hoses
BOB STEWARD, A&P-IA:
There is no “legal” involved, as they are not life or calendar limited parts per Beech. Calendar-based hose replacement is “recommended” industry practice. Anyone who has the forward mounted oil cooler had better try and flex those hoses. They’ll likely sound like rice crispies crackling. That long stretch running past the exhaust pipes gets cooked, even with firesleeve on the hoses. I rescued one plane out of a cow pasture; the hoses burst in flight, spraying oil on the windshield (amazing how leaky the cowl is), and filling the cockpit with smoke.
I don’t see why the Teflon would not work for the gear. I don’t personally care for them, as they are quite a bit stiffer than the Aeroquip 303 or the Stratoflex 111.
I don’t accept the “unlimited life” suggestion on the Teflon. Everything wears out eventually. It might be double or even triple the life of the rubber hoses, but I’d still replace them after 20 years if I found them on
a plane.
Firesleeving is a good idea, if the hoses are inside the cowl; a waste of money if they are in the cabin.
TECHNICAL EDITOR’S NOTE, MIKE RELLIHAN:
To further expand on Bob’s comments, I’d like to mention that most sources seem to promote a five year shelf life limit on rubber-based hose, and a five to seven year in-service life. In reality, most A&P experience is that if the hoses are properly selected, are firesleeved when warranted, and are properly installed (good support, no stretch, no twist, etc.), a ten year service life is probably reasonable. Nearly all the reported failures on original hoses have come from installations that were 15 years old or older; some as old as 35 years (which is remarkable). To qualify this life expectation, this assumes that the hoses are being examined for correct function and condition, no seepage or leaks, proper installation, and are not being frequently removed and reinstalled. Variances naturally warrant more frequent replacement.
Firesleeving is known to provide some degree of added heat protection. It is also supposed to provide a safety factor against severe leakage. This works only if the firesleeve is correctly installed, with metal banding securing the ends, plus sealant. The idea is that the sleeve will temporarily contain a serious leak, with only minor seepage or swelling showing a warning of a failing hose. Hopefully you will have time to spot an oil hose or fuel hose leak, before it bites you in flight. Note that firesleeve installed with bare safety-wired ends won’t provide much leak protection. You aren’t getting the full value of your firesleeve dollar, if it isn’t correctly applied. Since leakage is usually quickly spotted in the airframe, and isn’t as great a risk when aft of the firewall, most folks don’t consider firesleeve worthwhile outside of the engine compartment.
Teflon tube hoses have an unlimited shelf life. While the FAA and the manufacturers consider them to also have an unlimited service live, many of us consider their service experience to have been too short to conclusively show that. My personal experience is that they are nearly as flexible as standard hose when new, but that they typically “take a set”, and harden somewhat, in service. This is particularly true in hot oil service. Once in service for some time, one of these hoses will typically retain its installed shape when removed, much like an age-hardened rubber hose. I can’t help but wonder what is happening in the liner when a stiff tube has to be repeatedly flexed to get it in and out (for example). My personal conclusion at this point is that the Teflon hoses probably do have an unlimited life in many applications. An example might be a flexible fuel line between fuselage and wing. They are also probably long-lived when they remain in the same application and position, aren’t bent beyond their specs during removal and installation, and are very seldom removed and reconnected. I would be much more skeptical of hoses that have been switched between fuel and oil, have been installed with different positioning, are subject to vibration having large excursions, or which are frequently removed and reinstalled.
Advantages and disadvantages:
To my knowledge, the readily available Teflon hose is rated only for medium-pressure service, with an upper limit of 1,500 PSI. This makes it rather marginal for brake lines, and unsuitable for retract systems. I do not use or recommend it for either of these applications, though I know it has been successfully used in brake service.
In addition to service life, the Teflon has the advantage of being significantly smaller in OD for a given size ID. The internal fitting and tube size still meets standard specs, and the actual flow rates often exceed the rates of standard hose, due to the low-friction lining surface. When coupled with the option of extruded firesleeving (molded onto the outer stainless steel braid of the hose and hose ends), the smaller OD can make a dramatic difference in tight spaces. For example, the oil cooler lines wind up being nearly one-half the outer diameter of standard firesleeved hose. This can be a huge advantage on tightly cowled homebuilts, and a significant advantage on many certified planes.
The smooth extruded firesleeving looks much neater than the usual wrinkled firesleeve, requires no end banding, and is much easier to keep clean.
Precision Hose Technologies sells to A&P’s and FBO’s at a discount, and will sell direct to BAC members at the FBO discount price. The A&P/FBO price spread is intended to reimburse those agencies for their work in research, order processing, and payment handling; they are also assuming responsibility for getting the right thing. They certainly earn and deserve the price difference, as with any other service provider. PHT does maintain a kit reference file, and can provide a firewall-forward hose kit for nearly any make and model. I always consider it to be worth the shipping cost to send in your old hoses instead. Having them copy your old hoses has several advantages. If you want one longer or shorter, you can say so. You can also request a different end fitting, such as a 90-degree in place of a straight fitting, if it will help with some fit or clearance problem. Copying also helps ensure that any previous changes are accommodated in the new hoses; you never know when some earlier change was made in the hoses, for some good reason. The original kit specs may or may not reflect what you really have and need.
One last thing. All new hoses should be pressure tested before being placed in service. Few field fabricators have that capability. It probably makes little difference in something like a fuel pressure gauge vent line. However, (for example) I don’t plan to trust my life to a set of oil cooler hoses that were field-fabricated and installed untested. I know that they can be fine, and that thousands are no doubt successfully flying today. At the very least, if you will be flying field fabricated hoses, do a high-speed but aborted takeoff attempt (assuming enough room, of course). This will let the engine almost reach peak RPM while still cool (thus max cold oil pressure), along with max fuel pressure. Then taxi back in and check everything out before flying. This is a good idea even with factory hoses, to verify the quality of the installation. Just keep in mind that factory hoses are proof tested to at least 150% of the maximum rated working pressure, and often to 200%. That means that a factory Teflon hose rated to 1,500 PSI has usually been tested to 3,000 PSI, and will be in oil cooler service at a maximum 100 PSI. If you install an untested field assembly and do a run-up and aborted takeoff test, you have tested it to 100 PSI… your normal working pressure. You have no clue what the safety margin is.
If your A&P or shop wants you to handle getting certified hose assemblies (complete with certification ID bands and paperwork), and they will be supervising your installation of these hoses, and you are willing to assume much of the responsibility for handling shipping of your old hoses (and getting back the right new ones), you can contact PHT to get a price and place an order. This is another money-saving benefit for BAC members.