Flow measurement using orifice plate

Hi ,

May be this will help

Flange Taps

Flange taps are holes drilled into a pair of flanges. Flange tap holes are not recommended when the pipe size is below 2 inches.

Pipe Taps

Pipe taps are located at 2 1/2 pipe diameters upstream and 8 diameters downstream from the orifice plate. Exact location of the taps is not critical. However, the effect of pipe roughness and dimensional inconsistencies can be severe. The uncertainty of measurement is 50 % greater with full flow taps than with taps close to the orifice. Pipe taps are not normally used unless it is required to install the orifice meter on a existing pipe, or other taps (such as radius taps or vena contracta taps) cannot be used.

Corner Taps

Corner taps are used when the pipe size is 2 inches or less.

Vena Contracta Taps

When an orifice plate is inserted into the flowline, it creates an increase in flow velocity and a decrease in pressure. The section downstream of an orifice bore shows an increase in velocity and decrease in a pressure at a point called a "vena contracta point." The location of the vena contracta point is between 0.35 to 0.85 of pipe diameters downstream of the plate, depending on the beta ratio and Reynolds number. Vena Contracta taps are located 1D upstream and at the Vena Contracta location downstream. Vena Contracta Taps are the optimum location for measurement accuracy. They are not used for pipes less than 6" in diameter.

Regards

Jose John

may I ask a question?

does the tapping points affect the reading (thats logical) but how it affects the reading? or in another way vena contarcta tapping is not like flange tappings so the drop in pressure at a same flow for the two types will be different, where can i find that effect in Bernoullis equation?