Static Tap - Rectangular, Component Type
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 ans the concrete conduit
in which the high pressure tap shall be installed. This section shall also incorporate a hydraulic shape
employing one vena contractae. The throat section shall include a second 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 or conduit size.
The tube shall be of the component type with flat invert and crown to prevent accumulation of solids at the
invert and gases at the crown upstream of the throat section. The components shall consist of an inlet
pressure sensing pad and a throat section designed for key licking into the concrete channel.
The inlet pressure sensing pad shall be fabricated of stainless steel plate, ASTM Designation A240 or A167,
Type 304. The throat section grouting member shall be constructed of carbon steel channel, ASTM
Designation A36 to which is welded an inner trim of stainless steel plate, ASTM Designation A240 or A167,
Type 304.
The manufacturer of the Venturi components shall provide the Contractor with dimensions, grouting
instructions and finishing details for the inlet and outlet cones.
The metering element 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 of flow in the flow range indicated in the tabulation.
The Venturi shall be a BIF Model 20184 or approved equal.
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