 |
    |
 |
|
|
Plumber's Nightmare – Part 3
|
 |
|
Getting Hosed
|
Text and photos by Wayne Scraba |
"Hose is hose - who cares?” Hang on one second: Not only are there specific types of A-N hose out there, there are a number of different applications for the stuff. For example, the hose used in a certified aircraft is different from the hose you use in a race car. It might look the same on the outside, but internally, there are major variances.
In order to build a high quality plumbing package for your race car, you have to consider the types of hose commonly used: One (and I'm using Aeroquip hose as the example here) is based upon a braided steel exterior along with an "elastomer" inner liner. Aeroquip incorporates a patented "AQP" material for the elastomer. Basically, this inner hose is a synthetic rubber tube that has a "clean" inside diameter and flows very well. Furthermore, it can withstand continuous operating temperatures from -55° F to over 300° F and is designed to have an operational vacuum service limit of 28 inches/HG (the exception is -32 hose, which has a vacuum service limit of 15 inches/HG). The inner liner is wrapped with a special braid that is in turn bonded to a rubber jacket. Finally, the hose is covered with a stainless steel wire braid and all of these pieces are bonded together. This type of hose is capable of withstanding considerable pressure and heat. And because of this, it can be used for almost all fluid transfer applications except brake lines. Hose of this type is commonly sold by Aeroquip under the AQP Racing Hose model line. Specifications for this type of hose are as follows: AQP Hose Specs... Dash Size Hose I.D. Hose O.D. Maximum Minimum Minimum Weight Operating PSI Burst PSI Bend Radius (per foot) ____________________________________________________ -4 .22 in. .44 in. 1000 6000 2.00 in. 0.11 lbs. -6 .34 in. .55 in. 1000 6000 2.50 in. 0.16 lbs. -8 .44 in. .65 in. 1000 5000 3.50 in. 0.17 lbs. -10 .56 in. .80 in. 1000 5000 4.00 in. 0.21 lbs. -12 .69 in. .94 in. 1000 4000 4.50 in. 0.29 lbs. -16 .88 in. 1.15 in. 750 3000 5.50 in. 0.38 lbs. -20 1.13 in. 1.41 in. 500 2000 8.00 in. 0.49 lbs. -24 1.34 in. 1.70 in. 50 200 9.00 in. 0.80 lbs. -32 1.75 in. 2.09 in. 50 200 12.50 in. 0.98 lbs. Another type of hose that you should concern yourself with has a TFE (Teflon) core. Basically, this hose uses an extruded Teflon tube on the inside that is compatible with all brake fluids. This hose has a stainless steel single wire braid cover. The operating range is between -100° F to + 450° F and a maximum vacuum service limit of 28 inches/HG. Applications include brakes, hydraulic system actuation, high pressure engine instrumentation and so on. Hose of this type is sold by Aeroquip under the TFE Racing Hose model line. Specs are as follows: TFE Hose Specs... Dash Size Hose I.D. Hose O.D. Maximum Minimum Minimum Operating PSI Burst PSI Bend Radius _______________________________________________________________ -3 .13 in. .25 in. 3000 12000 1.50 in. -4 .19 in. .30 in. 3000 12000 2.00 in. One more type of hose, and one that's relatively new is called "Startlite". Essentially, this is a special hose that is up to 45% lighter than standard hose. It is designed with a fire retardant Nomex cover and patented AQP elastomer tube liner (smooth bore construction -- some types of lightweight hose use a convoluted Teflon core, which as you can imagine, can constitute a rather healthy flow restriction). The Nomex cover eliminates the need for firesleeve type protective cover required by stainless braided hose. StartLite hose assemblies are 45% lighter in weight than conventional high performance stainless braided hose assemblies but has an operating pressure of 200 psi in all sizes and a five to one safety margin at + 300 deg. F. All sizes are vacuum rated up to 20 in. Hg.
Startlite Hose can use either standard reusable Aeroquip hose ends or, for the ultimate in weight saving, aluminum crimp, style swivel fittings. Either are available in sizes -4 through -16. Crimped hose ends must be installed using the Aeroquip Pro Crimp 1380 assembly machine (which a number of Aeroquip distributors have on hand). Aside from it's rather hefty buy-in cost, fly weight hose such as Startlite is not as strong as it's stainless-steel braid covered cousins. It simply doesn't have the abrasion resistance. In addition, it doesn't have the ultimate pressure handling capabilities of other more common hose. Specifications for Startlite hose are as follows: Startlite Hose Specifications... Dash Size Hose I.D. Hose O.D. Maximum Minimum Minimum Weight Operating PSI Burst PSI Bend Radius (per foot)
__________________________________________________________________ -6 .34 in. .55 in. 200 1000 2.50 in. 0.08 lbs. -8 .44 in. .64 in. 200 1000 3.50 in. 0.11 lbs. -10 .56 in. .80 in. 200 1000 4.00 in. 0.14 lbs. -12 .69 in. .93 in. 200 1000 4.50 in. 0.16 lbs. -16 .88 in. 1.15 in. 200 1000 5.50 in. 0.25 lbs. We're not done: When searching for hose, you'll often come across genuine "aircraft hose". And this stuff differs from the hose a racer normally uses. The most common is "Medium Pressure Coverless Engine Hose". Using Aeroquip 601 hose as the example, this hose is designed specifically for aircraft power plant and air frame fuel and oil lines. It's available in a wide range of sizes (from -3 all the way up to -32, including the -5 size which is not used in drag racing), and conforms to MIL Spec H-83797. It has an operating range of between -65° F to +275° F. In terms of construction, the inner tube is a seamless, specially formulated synthetic rubber compound. The reinforcement and cover consist of a stainless steel wire braid, which includes a partial inner braid and a full coverage outer braid. In order to identify the hose (and obviously, to placate aircraft mechanics as well as FAA inspectors), a tape showing "Aeroquip 601 - size", a manufacturer's code and a hose cure date is applied to the bright wire outer braid at regular intervals. The specifications for this hose are as follows: 601 Hose Specifications... Dash Size Hose I.D. Hose O.D. Maximum Minimum Minimum Weight Operating PSI Burst PSI Bend Radius (per foot) _______________________________________________________ -3 .156 in. .375 in. 1000 3000 1.75 in. 0.096 lbs. -4 .219 in. .438 in. 1000 6000 2.00 in. 0.120 lbs. -5 .281 in. .484 in. 1000 6000 2.25 in. 0.144 lbs. -6 .344 in. .547 in. 1000 6000 2.50 in. 0.156 lbs. -8 .438 in. .641 in. 1000 5000 3.50 in. 0.168 lbs. -10 .562 in. .797 in. 1000 5000 4.00 in. 0.204 lbs. -12 .688 in. .938 in. 1000 3750 4.50 in. 0.288 lbs. -16 .875 in. 1.156 in. 750 2500 5.50 in. 0.384 lbs. -20 1.125 in. 1.437 in. 500 2000 8.00 in. 0.492 lbs. -24 1.375 in. 1.704 in. 250 2000 9.00 in. 0.672 lbs. -32 1.781 in. 2.094 in. 200 1200 12.50 in. 0.900 lbs.
If you take the time to compare 601 hose to AQP hose, you can see there are many similarities, and as you can see, several differences. You'll also find that the "certified" hose is extremely expensive when compared to conventional race car hose. Why? That's simple. The aircraft end user is paying for a larger amount of checks and balances (in simple terms, quality control measures). Does this mean that the 601 hose is superior to AQP? Probably. Does it mean it's better for a racing application? Probably not. You'll also find that even though the minimum bend radius dimensions are similar between the two types of hose, AQP is generally easier to work with because 601 hose is stiffer.
Another point to consider is this: Aircraft hose such as 601 is designed to function with a "cutter" style of hose end, while AQP isn't. Hose ends which physically cut the hose are more difficult to assemble, and although advertised as re-usable, once installed and then removed, they take quite a bit of work to clean before reuse (cutter hose ends physically cut the hose, and the residue is left on the threads of the hose end). Additionally, the cutting action mandates that the hose be shortened each time the hose end is removed and re-used. Another aircraft hose configuration you'll likely come across is "AE318" or 4000 PSI Wire Braid Reinforced Teflon Hose. This is an advanced high pressure hose that is primarily used on aircraft hydraulic systems (to give you an idea, this hose is used on the B2 Bomber). The hose reinforcement consists of stainless steel braids (-4) and a combination wire braid and spirally applied steel wire wrap in other sizes (-6 through -20). The extruded Teflon tube has a smooth bore which, for all intents and purposes is compatible with most fluids used in aviation or motorsports. Because the Teflon hose has essentially zero moisture absorption, the shelf life is virtually unlimited (keep in mind that other hose configurations can eventually deteriorate). It has a wide temperature range from -65° F to + 400° F. Specifications for this hose are as follows: AE318 Hose Specifications... Dash Size Hose I.D. Hose O.D. Maximum Minimum Minimum Operating PSI Burst PSI Bend Radius _____________________________________________________________ -4 .212 in. .470 in. 8000 4000 3.00 in. -6 .298 in. .580 in. 8000 4000 5.00 in. -8 .391 in. .710 in. 8000 4000 5.75 in. -10 .500 in. .800 in. 8000 4000 6.50 in. -12 .681 in. 1.055 in. 8000 4000 7.75 in. -16 .875 in. 1.320 in. 8000 4000 9.63 in. -20 1.110 in. 1.590 in. 8000 4000 12.50 in.
It's easy to see that this hose has considerable burst pressure capability, right on through the largest sizes. But for a racing application, the pressure capabilities are likely excessive. Another shortcoming for race applications is the bend radius. As you can see, the hose is very stiff and not easily managed. This is outstanding quality hose, but for the most part, overkill for a race car. "AE645" is a Nomex reinforced, convoluted Teflon hose. It's essentially the aircraft equivalent of Startlite, but with some important differences. For example, the inner liner is convoluted instead of straight. This means the inside of the hose is corrugated like a drainage culvert. This is fine for the intended application, however in a race car, there is a need to concern yourself with laminar fluid flow or the flow of fluid near the wall of the hose. Some tests I have been advised of have shown that convoluted hose will flow less than an equally sized smooth bore hose (hence the use of a smooth liner in Startlite). In addition, AE645 can make very tight bends where Startlite can't. The specifications for AE645 are as follows: AE645 Hose Specifications... Dash Size Hose I.D. Hose O.D. Maximum Minimum Minimum Weight Operating PSI Burst PSI Bend Radius (per foot) __________________________________________________________________ -6 .355 in. .575 in. 300 N/A .75 in. 0.08 lbs. -8 .510 in. .760 in. 250 N/A 1.00 in. 0.12 lbs. -10 .600 in. .870 in. 250 N/A 1.50 in. 0.15 lbs. -12 .765 in. 1.075 in. 200 N/A 2.00 in. 0.19 lbs. -16 .980 in. 1.315 in. 200 N/A 3.00 in. 0.25 lbs. With the above, it's easy to see that not all hose is created equal (even within specific manufacturers). Buy the right stuff before you get hosed. For a closer look check out the accompanying photos.
|
