I sure wish people would base their observations and opinions on hard data, when it is readily available. I don't mean to discredit intuition and experience altogether, as both can be priceless, but in cases such as this, there are hard facts available. Who are "the hose guys"?

The "stiffness" of new Teflon-lined hose is a lot of crap. I have installed several dozen, and find them to be as flexible or more flexible as rubber hoses. I have pasted in a chart that shows that the 124 Teflon has the same bend radius as the 111 rubber in the larger sizes, and an even smaller bend radius in the smaller sizes. The formatting will probably get hosed (it's a pun) by the mail lists, but Ron should receive it OK. I have included the link so others can view it, as well as other data. The fact is, the smaller OD of the Teflon 124 hoses helps them fit in many tight places with less of a bend radius than rubber would require (or did require). The "stiffness" OWT is related to the tendency of the hose to "take a set" following some time in service. All hoses do this to some degree. As long as the hose remains in the original service, this set can actually help. It means that the hose has adapted itself to its position. No hose, whether rubber or Teflon, should be deliberately bent to opposite extremes when removed for service.

If this isn't enough, consider that regular rubber hose has a nominal five-year shelf life, and a nominal five-year service life. The manufacturers and the FAA have assigned an unlimited shelf and service life to Teflon hose. Personally, I qualify that to be an unlimited service life based on remaining in the original application and position, and on passing visual inspection. The Teflon has the same ID specs as the rubber hose, but often flows more due to the reduced drag in the liner.

Having said all this, I have encountered cases in which replacement hoses had been previously installed with incorrect fittings. If something seems to be bent too tightly, chances are it is supposed to have a different end fitting. Precision Hose Technologies has the tech specs for most planes. If you have a suspected incorrect fitting, they can advise you. There is also nothing wrong with solving a problem by using a better suited fitting. Just be sure that you understand all the factors involved. Hoses that have an angled fitting on both ends have a "clocking" specification, to make sure the hose is not twisted when installed. I normally recommend that the old hoses be sent to PHT for copying; either as-is, when all is well, or with requested changes (something longer or shorter, or with a different end fitting).

CHART:
Precision Hose Technology, Inc

Hose Minimum Bend Radius

Hose Minimum Bend Radius (inches)
Size 111 124 130 156/176 171 193 160
-2 - - - - - 2.00 -
-3 3.00 2.00 - 1.75 - 2.00 -
-4 3.00 2.00 2.00 2.00 1.50 4.00 3.00
-5 3.38 2.00 - 2.25 - - -
-6 4.00 4.00 2.50 2.50 2.50 4.00 4.50
-8 4.63 4.63 3.50 3.50 2.88 6.00 6.00
-10 5.50 5.50 4.00 4.00 3.25 6.00 7.50
-12 6.50 6.50 4.50 4.50 4.00 - 9.00
-16 7.38 7.38 - 5.50 - - 12.00

LINK:
http://www.aircrafthose.com/

Photo of a firesleeved 1/2" ID hose:
124J Stratoflex medium pressure hose



more pictures

124-8J hose with a 524-8CR fitting attached.


----- Original Message -----
From: ron mattson
To: musketeermail@yahoogroups.com ; bac-mail@beechaeroclub.org
Sent: Tuesday, August 30, 2005 2:34 PM
Subject: [BAC-Mail] Teflon Hoses


I am planning on replacing my hoses next month and can't seem to get a good feel for using Teflon hoses. On my Sierra the oil cooler hoses seem to have a short radius bend and with the Teflon hoses being stiffer I am afraid of kinking a hose. When talking to the hose guys they say that if you use Teflon hoses you will need more fittings because Teflon will not make the same radius bend as rubber. Thier opinion is the advantages of teflon do not override the the installation ease of rubber. ( with the hose fire sleeved you have a hard time telling if the hose is about to kink). Has anyone installed Teflon hoses specifically for their oil cooler where it is mounted on a bracket off the firewall about mid engine height. ( 1971 Sierra I0-360 ). By the way I was quoted a slightly lower price for firesleeved Teflon than Firesleeved Rubber.