Wednesday, February 01, 2012

Hose Flap

Hose Flap
Hose Flap from MIL-DTL-8794 hose

Stratoflex 111 or Aeroquip 303 Hose Assembly
I wrote an article a while back called "The Battle of the Bulge" that goes into some detail on how flaps are prevented, inspected for, and created. Here I want to go into some detail on how to inspect a hose assembly to detect a flap.

For straight hose assemblies you sight through the hose. Be sure to look into both ends, not just one end. The reason you need to look through both ends is that when you are sighting through the hose assembly you are looking for a flap at the far fitting. A small flap at the near fitting might be missed. Also, sighting through both ends is somewhat like taking a "second" look. Also, use a plug gauge like the one shown here.
Hose Plug Gauge for MIL-DTL-8794 Hose
For hoses with angle fittings where you cannot sight through the hose or use a plug gauge, you drop a ball through the hose. The ball is sized to be just a little bit smaller than the hose fitting inside diameter. For example, a dash 8 111 style hose assembly with 90 degree fittings takes a ball diameter of 0.320 inch. Caution: ball size changes for each type, size, and fitting style hose.

The third method of inspecting for flaps is to flow the hose and inspect how the stream of fluid leaves the hose. This is done during cleaning and as preparation for pressure testing the hose assembly. Typically, a TSO hose shop will use all three methods as part of their quality control system.

Minimum Diameter at the bulge When Hose is Assembled with Adapters per  MIL-H-8794D (obsolete)
-3 .080
-4 .132
-5 .200
-6 .260
-8 .350
-10 .450
-12 .575

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