Boost Venturi Probes are used to amplify the measured velocity pressure in a flowing
fluid. The measured total pressure is unchanged from a Pitot-Static
reading but the
flow is accelerated in the venturi passages, as in a
flow nozzle, so the static pressure
reading is lower than that obtained
with a Pitot-Static probe.
The magnitude of the boost or gain is defined
as: (PT2 - PS2)/(PT1-PS1) where PT2,
PS2 are total
and static pressures measured by the probe and PT1, PS1 are free stream
values as measured by a conventional Pitot-Static probe. The standard Boost
Venturi probes (Types A and B) provide approximate gain figures of 10
and 4.
By amplifying the velocity pressure difference (PT - PS) with
a Boost Venturi, a more
accurate measurement can be made of this difference.
This increase in accuracy will
be achieved, however, only if the
probe's gain is accurately known, and this may
require that the probe
be calibrated under actual flow conditions.
When used for monitoring
a fixed flow, a Boost Venturi gives a lower permanent
pressure drop than
an orifice. These probes may also be used with a differential
pressure
controller to perform flow control and / or limit functions.
TYPE
VA
Large outer venturi encompassing smaller inside venturi for maximum
gain of 9 plus.
TYPE VB
Smaller more compact venturi for maximum
gain of 3 plus.
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