Static Tap - Rectangular, Fabricated
The metering design shall be of the pressure differential producing type utilizing pure static
pressure sensed at the inlet and throat sections.
The inlet section shall be comprised of a rectangular section of similar dimensions as those of the
conduit. The high pressure tap shall be included in this section. This section shall include 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 shall be at least 0.5 times the equivalent
throat diameter. The low pressure tap shall be located in this section. The outlet section shall be
truncated, having an included angle of 10 degrees.
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 about 75,000 or greater and independent of beta
ratio of line size.
The tube shall be fabricated with a flat invert and crown to prevent accumulation of solids at the
invert and gases at the crown. The inlet and outlet sections shall be fabricated of carbon steel,
ASTM Designation A276, Type 304. The throat section shall be fabricated of stainless steel,
ASTM Designation A167, A240, or A276 Type 304. The ends of the tube shall be as indicated
in the tabulation.
The entire tube except the throat and pressure connection bushings shall not have debris
collecting cavities or annular chambers, but shall have single pressure connections at the inlet and
throat.
Prototype testing of a model having hydraulic similitude shall be included.
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 % of pipe velocity head and shall
provide proof that the coefficient is independent of line size and beta ratio.
The accuracy shall be ± 1% of actual rate in the flow range indicated in the tabulation.
The Venturi shall be a BIF Model 20184 or approved equal.
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