The Primary Element shall produce a differential pressure, which is proportional to the square of the flow rate through the device, utilizing static pressure sensed at the inlet high pressure tap and the low pressure throat tap.
The Primary Element shall be fabricated in accordance with A.S.M.E. specifications and recommendations. The inlet section shall consist of a straight pipe section of like diameter to the preceding pipeline, and an entrance cone with an A.S.M.E. specified 21 degree angle of convergence. The throat shall be a straight cylindrical section at least 0.5 times the throat diameter. The outlet section shall be an exit cone with a A.S.M.E. specified 15 degree angle of divergence. Recovery cone may be truncated as permitted by A.S.M.E. standards. Recovery cone may also be elongated to further minimize permanent pressure loss.
The Primary Element shall be furnished with two pressure sensing taps; one in the straight inlet pipe section (upstream tap) and one in the throat section (downstream tap). There shall be no annular chambers or slots within the Primary Element.
The Primary Element body shall be constructed of either rolled ASTM A 285 C carbon steel or _______________, and the throat section constructed of 304 Stainless Steel or _____________ The Primary Element shall have a discharge coefficient that is constant over the normal range of flow; independent of Beta Ratio or line size.
The Primary Element shall have an uncalibrated accuracy of +/- 0.75% of actual flow for the range specified. The device shall be a Lambda Model 3500 or approved equal.