bent pipes are the same diameter throughout the entire pipe.
For example, a stock bend will constrict the pipe through
the bend, but a mandrel bend remains the same diameter even
through the bend radius. Notice in picture below, the Stock
bent pipe (A) is smaller in diameter through
the bend, while the Mandrel bent pipe (B)
does not change in diameter.
consistent diameter of the Mandrel bend reduces the restriction
by roughly 25% as compared to factory bends. The result:
Mandrel bent pipes give you up to 25% more flow than
compression bent pipes.
bending can create a bend much tighter than non-mandrel pressure
bending. Bending companies refer to the bending dies as mandrels
or shoes. Technically the mandrel is a part of the tooling set
but does not exist in most bending applications. The mandrel
actually goes inside the tubing and is held by a mandrel rod
to support the tubing at the tangent point of the bend. The
mandrel is then extracted after the bend is complete or within
the last few degrees of bending.
results in the tubing being the same diameter through the
straight tubing as in the bend radius. So if you started with
2" pipe and bent it into a 180-degree bend, it is still
2" through the entire bend radius.