The Army has two acceptable methods of tube cutting.
accurate and commonly used method is with the standard tube cutting
tool. When properly used, this tool leaves a smooth end on the tube
square with its axis. The second method of tube cutting is by using
a fine tooth hacksaw.
This method does not provide the square cut
produced with the standard cutting tool and necessitates filing the
tube end after cutting a square off the ends.
A variety of tools and methods are available for tube bending, each
having capabilities and advantages applicable to a particular type or
size of tubing.
Regardless of the method used, the object is to
obtain a smooth, even bend without flattening or buckling.
The two most common types of connection used with aircraft tubing are
the MS flareless and the flared connection.
The MS flareless
connection has distinct advantages over the flared connection: it is
easier to construct, has three load points to prevent leaks (as
opposed to one for flared connections), and can be used many times
Flared connections are formed by means
of a flaring tool.
When properly formed, they are capable of
withstanding high pressures and are used extensively in hydraulic
One of two kinds of flares can be used depending on the
type of tubing being used. Single flares are used for all sizes of
5052 aluminum alloy tubing with outside diameters greater than 1/2
inch. Double flares are used on all sizes of tubing with an outside
diameter of 1/2 inch or less. The third type of connection used in
aircraft plumbing systems is the beaded connection.
This type of
connection is not capable of withstanding high pressures and is used
only in low-pressure systems.
Fittings are used in aircraft plumbing systems to connect the various
lines with each other and with the components they operate. Prior to
installation all fittings must be inspected to ensure their surfaces
are smooth and then coated with the appropriate lubricant.
Fitting nuts must always be tightened with torque-indicating wrenches
to ensure the proper seal.
Overtorquing of these nuts can severely
damage the tubing assembly.
Likewise, under-torquing can allow the
line to blow out of the fitting or to leak under pressure.
When a damaged tube is discovered, the ideal solution is to replace
the complete section of tubing.
When this is not possible, minor
dents, nicks, and scratches can usually be