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This month’s Tool of the Month is actually a refinement of a homebrew tool we came up with while building AN hose for a recent fuel system installation. When you are building braided lines for your fuel system (or any fluid-transfer system, really), leaks happen. They can be due to a bad fitting, a bad assembly, or just bad luck, but they aren’t the end of the world to remedy.
What really sucks, however, is when you identify that leak after hours of reassembling the system you are working on, and the leak is in the most inaccessible spot imaginable, requiring hours of work to undo all the work you just did to fix the root cause of the leak. It’s a lot more convenient if you can identify a leak as soon as you assemble the line. We previously showed you our cobbled-together solution to the issue. Now, we’ve refined it into a full-blown kit, in order to test everything from -4 to -10 AN lines with the associated part numbers.
All you need to make a line tester is an appropriately sized AN plug, AN-to-1/4-inch NPT fitting, and a 1/4-inch NPT Female air line quick disconnect fitting.
The idea behind the tool is that, once you’ve assembled your line, you use an AN plug of the appropriate size in one end of the hose and connect the other end of the hose to a compressed air source. As we found the first time we tried to cobble everything together, is the local hardware store, no matter how well-stocked, is not your friend for these parts. You need actual AN fittings. For those, we turned to the Vibrant Performance catalog to source all of the parts needed to build a complete testing kit.
The key to these testers, in our opinion, is the 1/4-inch NPT male to AN fitting. 1/4-inch NPT is an extremely common air compressor size, and surprisingly, the AN-specific conversion fittings are quite affordable. Since proper assembly of the NPT fittings into an air hose quick disconnect fitting requires Teflon pipe tape, we decided that we should get a separate air hose fitting for each size adapter, and keep them permanently mated.
Assembly is like any other NPT fitting, a couple turns of Teflon tape in the proper direction, and then tightening everything up. The only difference is to make sure not to overtorque the fittings, since at least one of them will be aluminunm. In this case, both are aluminum.
Since we were already on the hunt for a four-pack of female NPT air hose fittings, we also decided to go a step further and look for aluminum fittings, to match the aluminum AN fittings. Most hardware store fittings are made from brass or steel, and while there’s nothing inherently wrong with either of those materials, having both fittings be the same material — aluminum — lets us sleep better at night. So, for a whopping $16, we ordered a kit from Amazon – it even comes with extra Teflon tape.
With the air line fittings in hand, it’s as simple as Teflon-taping our NPT-to-AN adapters from Vibrant, and tightening the two fittings together. Then, we connect the adapter to one end of the hose to be tested and use the appropriately sized AN plug on the other end. Plug the whole assembly into an air supply regulated to 50 or so PSI, and then submerge the plugged end into a container of water to look for bubbles. Once satisfied, flip the adapter and plug and repeat the process on the other end of the hose. Easy as pie.
From left to right: One end of the hose to be tested is fitted with the AN plug. The other end is fitted with the air line quick disconnect to AN assembly, and then plugged into a regulated air supply; we like 50psi. Then, the plugged end is submerged in water to watch for bubbles. Ideally, you'd use a nice clear container, not one that has outlived it's useful life in the kitchen, like we did here.
This easy, efficient test setup is inexpensive enough to just keep on hand, so that you can ensure that whenever you assemble braided hoses, you can easily test them before you spend hours under the car running line and connecting fittings, only to have to start over because something is leaking. All the Vibrant Performance AN fittings and plugs required for the full four-size kit are less than $65 from Summit Racing. Add that to the air line fitting kit from Amazon, and you’re well under a hundred bucks to be able to test anything from -4 to -10 lines. Pretty cheap peace-of-mind, if you ask us.
These are the Vibrant part numbers needed to build testers for lines ranging from -4 to -10. From Summit, all eight pieces come out to less than $63. Meaning that each size costs less than $20 in fittings.
