Static Tap - Cast Iron 4"-96"
The metering design shall be a differential pressure producing type, utilizing pure static pressure
sensed at the inlet and throat. The differential pressure shall indicate static pressure change only.
The entrance section shall be a cylindrical section of similar diameter as the pipe in which the
meter is being installed. The high pressure tap shall be installed in this entrance section. The inlet
section shall incorporate a hydraulic shape employing at least two vena contractae to condition
the flow pattern before it enters the throat section. The throat section shall be a cylindrical section
with a length at least 0.50 times the throat diameter. The low pressure tap shall be installed in the
throat section. The pressure recovery section (outlet cone) shall be truncated and have an
included angle of 10 degrees. The metering element shall not have debris collecting cavities or
annular chambers, and shall have a single pressure connection at the inlet and throat. Vent ports
and drains shall be included on a 90 degree plane to metering taps.
The flow meter body shall be constructed of cast iron, ASTM specification for Gray Iron castings
for Valves, Flanges and Pipe Fittings, Designation A-126, Class B. The throat liner and pressure
tap bushings shall be Bronze, Brass or 316 Stainless Steel. The flow meter flanges shall be 125
lb, or 250 lb, rating. The flow meter shall be hydrostatically tested at twice the working pressure
for a period of not less than 10 minutes.
The entire flow meter except the throat liner and pressure tap bushings shall be coated with an
epoxy paint which meets the requirements of NSF Part 61, for contact with potable water.
The manufacturer shall furnish data substantiating meter proportions and performance which
should include: Meter coefficient value and tolerance, proof that the coefficient is constant above
a Reynolds Number of 75,000 and independent of beta ratio and line size, the value of the
permanent head loss as a percent of the differential pressure produced, a flow versus differential
curve for the specific application described, and data showing the effects of typical installations
of fittings immediately upstream of the meter; including increaser, decreaser, and elbow. All
submitted data shall be certified by the manufacturer.
The un-calibrated accuracy of the flow meter installed per the manufacturers recommendation
shall be ± 0.50% of actual flow rate over a range of at least 10 to 1. This accuracy shall be
substantiated by a two times standard deviation calculation of at least 30 calibrated flow meters
of different line sizes and beta ratios. The manufacturer shall warrant the flow meter for a period
of not less than 25 years against defects in materials and workmanship.
The meter shall be a Model 20181 as manufactured by BIF and shall satisfy all project
requirements, or an approved equal.
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