LG Series Flow Measurement Throttle Devices0 pages

LG Series Flow Measurement Throttle Devices
Throttle orifice
Injecting nozzle device
Direct-reading throttle orifice flow meter
Venturi tube throttling device
Part one Summary
Preface
Throttle device is the most historic and most extensively used flow measurement instrument. It features itself
simple structure, easy installation, stable performance and high accuracy, etc merits. It can be used for flow
measurement for liquid, steam and gas in modern industries. There are many kinds of throttling devices with a
whole variety (being conformability with Standard GB/T2624, Standard ISQ5167-1-1991, Standard BS1042-1989
and Standard ASME) that are manufactured with advanced calculation methods and precise manufacturing means.
They are applied extensively in petroleum industry, chemical industry, electrical power industry, light industry,
water supply field, gas transmission field etc.
Principle of operation
A throttle element (throttle orifice, throttle nozzle) is installed in a pipe that is full of one way flowing continuous
fluid. When the fluid passes the throttling orifice of the throttling element, the fluid stream forms local
construction. Then the velocity increases, so does the kinetic energy, the static pressure decreases. So, there is
produced a differential static pressure from the fore and the rear of the throttling element, i.e. △P=P1-P2. If the
area of the throttle orifice is F, the mass flow of the fluid is qm, the volume flow is qv the density isρ,according to
the flow continuity law and Bernoulli equation, the following mathematical relations between differential pressure
and fluid flow can be derived:
qm=αF
or qv=αF
“α”is flow coefficient. According to the above equation, if the area of the throttle orifice and fluid density are
constant, flow has direct ratio with square root of differential pressure. If only you have the differential pressure
value, then you calculate the flow value. Throttling device can measuring fluid flow just according to this
principle.
Orifice plate throttle device
Nozzle throttle piece
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