do you know the tricks and the tiny mistakes that often go
unnoticed when building hoses?
| Firesleeve cut too short |
| all hose types
with Firesleeve |
Firesleeve needs to be cut longer than the
hose. The longer the hose or the tighter the Firesleeve the longer it
needs to be. Firesleeve cut too short will pull back from the fitting when
the hose is bent. This exposes the fitting. In a fire the fitting is the
weak point and needs to be fully protected. Such a hose no longer meets
its fire rating and should be fixed or removed from the aircraft.
|
end of socket should not be exposed |
| Nut and nipple assembly not fully
screwed into socket |
| all hose types - common problem |
If you don't have the correct tools it can be hard to get the nut and nipple
screwed together to the correct gap - especially if you stop turning half
way on. If you leave too much gap the fitting doesn't fully grip the hose.
Either get the correct tools or have someone who does fabricate your hoses.
If you inspect hoses and you see one with excessive gap then red tag the
hose - it's not airworthy.
|
Gap should be the width of the thin feeler gage in lower
portion of photo |
| Socket backed out of hose during
nipple-nut assembly |
| Stratoflex 156 or Aeroquip 601 hose |
A common problem. If you install the socket and then screw
the nut-nipple onto the socket you just pull the socket back out of the
hose. Then when the hose sees pressure, or some time later after vibration
shakes things loose, the fitting falls off. You must screw the nut-nipple
into the hose by clamping the nose and socket in place--not just the socket.
Place a back-off mark on the hose to check for any socket movement after
assembly. |
White back-off mark shows that hose didn't slip out of
socket during fitting installation. |
| Rubber flap cut into hose inner tube |
| Stratoflex 111 or Aeroquip 303 hose
(MIL-H-8794) |
The hose nipple is larger than the hose inner tube. As you screw the
nipple into the hose a bulge is formed in front of the nipple. The mandrel
is used to compress the bulge. The two
critical elements are the mandrel diameter and the speed at which you turn the nipple-- as the
bulge must move forward in front of the nipple--
Hand mandrels are undersized and therefore tend to cut
flaps. A proper sized mandrel is only 1 to 2 thousands smaller than the
inside diameter of a new nipple. Hand mandrels are usually 10 to 15
thousands smaller. More information on mandrels
You must be able to inspect the inside of the hose - either by
sighting down the hose or dropping a sized ball through the hose.
|
check the inside
of the hose for flaps and obstructions |
| Socket turned too far during installation |
|
Stratoflex 111 or Aeroquip 303 hose (MIL-H-8794)
|
When screwing the socket onto 111, 303 or
Mil-H-8794 hose you must stop immediately when the socket bottoms out on
the end of the hose. If you keep turning the threads the socket pressed
into the hose cover is stripped. This is the most common reason for this
type of hose blowing the fitting of the end of the hose. Common
if you turn the socket with a wrench or a machine so you can't feel the
hose bottoming in the socket.
|
immediately stop when hose bottoms out in socket |
| Socket turns on hose when screwing nut-nipple assembly onto
hose |
| Stratoflex 111 or Aeroquip 303 hose
(Mil-H-8794) |
The hose is ruined if the socket turns or even starts to turn when
screwing the nut-nipple assembly onto the hose. During a pressure test the
fitting will blow off the end of the hose at a low pressure rating. You
can't save it - start over. |
if the yellow socket turns then hose is ruined |
| Collapsed inner tube from improper assembly |
|
Stratoflex 111 or Aeroquip 303 hose (Mil-H-8794) |
This occurs when the nipple grabs onto the hose inner tube and tears if
from the hose. The inner tube ends up wrapped up inside hose. If you hear any crackling noise as you screw the nut-nipple
onto the socket, stop -- you have ruined the hose. Occurs most often
with -8 hose size.
Often the person assembling the hose thinks the hose is defective. Nope. It's not the hose - its the
technique. OK, so you've been making hoses for 30 years. The hose you buy
now is not the same as it was even 10 years ago. Learn and adapt to
changes. The hose nipple is larger than the
inner tube. Any lubricant you put on the nipple/mandrel is wiped backward.
The nipple sees dry rubber. If you stop turning the rubber grabs onto the
nipple. When you start turning the stuck rubber tears itself free from the
hose. |
|
| Improper assembly lubrication |
|
Stratoflex 156 or Aeroquip 601 |
Improper assembly lubricant can prevent fitting
from sealing or properly attaching to hose by creating a hydraulic lock.
Follow the manufacturer's instructions for assembly. |
During fitting installation hose inner tube squeezes
into area inside rectangle. If oil fills this area the inner tube cannot
squeeze into recess and fitting will leak or vibrate off of hose. |
Always use the hose manufacturer's publish instructions on how to
assemble hose assemblies
