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What should you do if you install a new hose and it leaks? If the old hose didn’t leak, your first assumption may be that the new hose must be bad, but this is not necessarily true. Identify the Leak The first thing that you need to do is properly identify the source of the leak. A hose leak usually occurs along the length of the hose, or where the hose exits the socket. Common leaks include: • Connection leaks • Leaks between the fittings • Leaks behind the nut When installing a replacement hose, leaks usually occur at the connection. Two conditions that may cause a connection leak are: • Connecting the new hose to an old fitting • When both fittings have hard mating surfaces, such as steel against steel. This is especially true when it is stainless against stainless. Why fitting connections leak The aircraft flared fitting seals by the mating of two flat surfaces against one another. If the two surfaces are not perfectly flat against one another, then the surfaces only make contact at the high points. Fluid then flows through the spaces. The surfaces need to be either: 1. Perfectly flat and parallel to one another, or 2. Able to deform to fill in the voids. The high points must get squished flat. Perfectly flat and parallel surfaces don't exist. Every surface has some roughness or blemishes. But the closer to perfection the better, since sealing surfaces need to be as good as possible. The sealing surface on the hose is new, so it's probably in good condition. But what about the sealing surface on the male nipple? Chances are that it wasn't replaced. The male nipple is most likely deformed as it had to be to seal the old hose. The fact that the old hose didn't leak means that the surfaces have deformed and sealed. The deformations in the older surface are going to get in the way and prevent sealing of the new hose. The harder the surfaces, the more likely you will have connection leaks. O-rings were invented for this situation. O-rings make one surface hard and one surface soft. The soft O-ring squishes and fills in any microscopic voids and distortions. Conical Seals With the trend towards using steel fittings, the use of conical seals is increasing. Years ago, when most fittings were aluminum on aluminum or steel on aluminum, conical seals were never required. A conical seal places a soft surface between our two hard sealing surfaces. This soft material deforms and fills in the voids. They are easy to use and inexpensive.

Hose fitting sealing surface