Static Tap - Fabricated Steel 6"-96"
The metering design shall be of the differential pressure producing type utilizing pure static
pressure sensed at the inlet and throat sections.
The inlet section shall be comprised of a cylindrical section of similar diameter as the pipe in which
the high pressure tap is installed and shall incorporate a hydraulic shape employing at least two
vena contractae to condition the flow profile before it enters the throat section. The laying length
of the throat section shall be at least 0.5 times the throat diameter. The low pressure tap shall be
installed in this section. The outlet cone shall be truncated having an included angle of 10º.
The differential pressure shall indicate static pressure change only. Devices employing entire or
partial Pitot effects, amplifying differential by changing flow direction at the point of sensing
pressure, thus introducing unwanted hydraulic noise, shall not be acceptable. The tube coefficient
shall be constant for pipe Reynolds number of 75,000 and greater and independent of beta ratio
and line size.
The inlet and outlet cones shall be fabricated of carbon steel, ASTM Designation A515, Grade 55,
60, 65 or 70 or equal pressure vessel material. The inlet pressure connection shall be of stainless
steel, Type 304, ASTM Designation A276. The throat section and trim shall be fabricated of
stainless steel, ASTM Designations A167, A182, A240, or A276, Type 304. The end of the tube
shall be as indicated in the piping schedule. The entire tube, excepting the throat liner and
pressure connection bushings, shall be coated with an epoxy paint which meets the requirements
of the United States EPA for potable water applications.
The metering element shall not have debris collecting cavities or annular chambers, but shall have
a single pressure connection at the inlet and throat. In addition, a stainless steel vent port and
drain shall be included on a 90º plane to the metering tap on the inlet section.
The approval data shall state and substantiate the value and tolerance of the coefficient, the effect
of up and downstream piping configurations, the head loss in percent of differential pressure and
shall provide proof that the coefficient is independent of line size and beta ratio.
The accuracy shall be ± 0.75% of actual rate of flow over the flow range indicated in the
tabulation. This accuracy shall be substantiated by a two times standard deviation calculation of
at least 30 calibrated tube coefficients of different line size and beta ratios.
The Venturi shall be a BIF Model 20183 or approved equal product.
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