In our last segment, we began our look at AN plumbing. We spun the clock back and determined the origins, and then went right into figuring out the “dash number” sizing system. To recap, you can determine (approximate) AN sizing by placing the AN number over 16 and dividing. Thus, a #6 hose over 16 equals 3/8-inch, or 0.375-inch. We also pointed that most automotive and aftermarket products are constructed with pipe threads, which rely upon interference fit to seal. AN products seal by way of the cone at the joint. The AN seal is much more reliable than the pipe thread seal and joints between AN components are easily disassembled and reassembled without the need for extra sealants. The difficulty arises when you have to mate the two (pipe thread to AN). What follows is a look at the mechanics of an AN fitting. The accompanying photos will also show you several (of many possible) pipe-thread-to-AN solutions companies such as Earl’s Performance offer. Check it out!
So what sorts of fittings (hose ends) are available? Different manufacturers offer different fittings; however, Earl’s Performance offers the largest cross section of available types. For the most part, straight, 30-degree “elbow” bend, 45-degree elbow bend, 60-degree elbow bend, 90-degree elbow bend, 120-degree elbow bend, 150-degree elbow bend and 180-degree elbow bend fittings are the most common. For most racecar and hot rod applications, straight, 45-degree and 90-degree bends are the most common. What’s with the “bent tube” part of the equation? Simple. In fittings with elbows or bends, the tube that joins the halves of the hose end (hose side and 37-degree flared side) is bent. The amount of the bend in degrees is what identifies the fitting.
That’s not the end of it, however: You can make a 90-degree bend with an AN fitting in more than one-way. One is a bent tube fitting (mentioned above). Another is a forged 90-degree fitting. When you think about it, a forged 90-degree fitting has the highest flow restriction of all fittings, as the fluid in the fitting must make an abrupt 90-degree turn. Basic straight fittings constitute the lowest flow restriction. If you need a bend in the system, if at all possible, use a bent tube fitting (this type of fitting incorporates a metal tube between the hose socket and the AN threaded end). These fittings have superior flow characteristics when compared to the forged 90° bends (forged 90-degree bends are the sharp right angle fittings you see). Forged 90-degree fittings (and 90-degree adapter fittings) should only be incorporated as the last resort where clearance is an issue.
While there are some exceptions, you can get the above fittings from Earl’s Performance for hoses sized AN 4 through AN 16. Earl’s “Swivel Seal” hose end fittings are designed to swivel. That means you don’t have concern yourself with orienting (indexing) the hose end prior to assembly (that isn’t the case with all hose ends). Another benefit of swiveling hose ends is the fact you can assemble them between respective components with ease. Plenty of hose ends are designed to be reusable, but most folks who use them will tell you while that’s possible, the fittings will usually get beat up after more than one install-remove process. They’ll work, but they likely won’t be too pretty. However, Earl’s offers replacement sockets. That means you can replace the typically beat up parts instead of throwing away the hose end.
As pointed out above, and shown in a preceding chart, AN fittings (hose ends and adapters) are engineered with straight threads. As we mentioned earlier, AN fittings do not rely upon an interference fit. Instead, the hose ends seal by way of a 37-degree flare or taper. The male fitting side has a 37-degree flare on the nipple, past the straight threads. The female fitting side has a 37-degree flare on the pocket, again past the threads. In operation, you tighten the fitting by way of the straight internal threads; the male and female 37-degree flares meet and tighten with the threads. Presto. Instant seal. It’s a brilliant idea.