Static Tap - Fabricated Insert 30"-96"
The metering design shall be of the differential pressure producing type utilizing pure static
pressure sensed at the inlet and throat sections.
The metering primary shall be designed for welding into the user’s pipe, and the Venturi
manufacturer shall provide details of pressure connection location and welding and the welding
procedure for securing the unit in the pipe. The high pressure connections shall be located in the
containing pipe as shown on the details.
The insert section 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 and protrude through the containing pipe.
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, A515, Grade 55, 60, 65, or 70. the
throat section shall be fabricated of stainless steel, ASTM Designation A182, A240, or A276 Type
304. The entire tube, except the throat liner and pressure connection bushing, 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 drain shall be included on a 90º
plane to the metering tap on the outlet attachment ring.
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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