venturi flow meter

venturi flow meter   Summary Throttle device is the most historic and most extensively used flow measurement instrument. Its features are 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 throttle devices with a whole variety (being
conformability with Standard GB/T2624-2006, Standard ISO5167-1-20031, Standard BS1042-1989 and Standard
ASME) that are manufactured with advanced calculation methods and precise manufacturing means. They are
applied extensively in petroleum, chemical, power, light industry, water supply field, gas transmission field etc. Principle of operation A throttle element (like throttle orifice, throttle nozzle, etc) 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 shrink. Then the velocity increases, so does the kinetic energy, the static pressure decreases. So, there is a differential static pressure from the fore and the rear of the throttle 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 is ρ, then 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. That is to say, if you have the differential pressure value, then you can calculate the flow value. Throttle device can measuring fluid flow just according to this principle. Table 1 Throttling element code and meaning

Code	Meaning	Code	Meaning
Y	Standard orifice plate	I	Eccentric orifice plate
Q	1/4 circle orifice plate	S	Segmental orifice plate
X	Small caliber orifice plate	Z	Raw cast contracted section (throat) Classic Wenturi Tube
T	Taper inlet orifice plate	J	Machined contracted section (throat) Classic Wenturi Tube
M	ISA1932 ejection nozzle	H	Iron plate welded contracted section (throat) Classic Wenturi Tube
C	Major diameter ejection nozzle	W	Wenturi ejection nozzle

Table 2 Pressure measuring code and meaning

Code	F	H	Z	D	T
Meaning	Pressure measuring with flange	Pressure measuring with angle joint ring chamber	Pressure measuring with drilling hole	Pressure measuring with two distanced holes	Special pressure measuring

Table 3 Nominal diameter code and meaning

Code				01		016		02		026		03		04		05		06		08		10
DN			mm	10		15		20		25		32		40		50		65		80		100
			in			1/2		3/4		1		1-1/4		1-1/2		2		2-1/2		3		4
Code				12		15		20		25		30		35		40		45		50		60
DN	mm			125		150		200		250		300		350		400		450		500		600
	in			5		6		8		10		12		14		16		18		20		24
Code					70		80		90		91
DN		mm			700		800		900		1000
		in			28		32		36		40

Table 4 Nominal pressure code and meaning

Code		01	02	03	04	05	06	10	11	15	16
PN	MPa	1.6	2.0	2.5	4.0	5.0	6.3	10.0	11.0	15.0	16.0
	Class		150			300			600	900
Code		25	26	42
PN	MPa	25.0	26.0	42.0
	Class		1500	2500