Dall Flow Tube
About Dall Flow Tube
The Dall flow tube consists of two
conical reducers inserted into the fluid-carrying pipe. It has a very
similar internal shape to the venturi tube, except that it lacks a
throat. This construction is much easier to manufacture than a venturi
tube which requires complex machining, and this gives the Dall flow
tube an advantage in cost over the venturi tube, although the
measurement accuracy obtained is not quite as good (approximately
±1.5%).
Another advantage of the Dall flow tube
is its shorter length, which makes the engineering task of inserting
it into the flow line easier. The Dall tube has one further
operational advantage, in that the permanent pressure loss imposed on
the system is only about 5% of the measured pressure difference and
thus is only half that due to a venturi tube. In other respects, the
two instruments are very similar, with their low maintenance
requirement and long life.

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