The differential pressure is measured through pressure taps located on each of the orifice plate.Pressure taps can be positioned at a variety of different locations.
FLANGE TAPS :
Flange taps are located 1 inch away from the face of the orifice plate both in upstream and downstream. In most of the cases flange taps are located on the flanges that hold the orifice plate in position.
CORNER TAPPING :
The tapping holes are in the corners of the flange. The tapping will be in angle to the flow direction. This type of tapping is used for pipe lines with diameter less than 2”.
PIPE TAPS :
Pipe taps are located at a fixed distance on the upstream and downstream of the orifice plate. The upstream pipe tap is located at 2.5 pipe diameter from the plate and the downstream pipe tap at 8 pipe diameter from the orifice plate. Pipe tap is also called as full flow taps.
VENA CONTRACTA TAPS (D & D/2 TAPS) :
At vena contracta point, the velocity will be maximum and the pressure will be minimum. The distance of vena contracta must be calculated from application data. On the upstream side it is located at one pipe diameter (1D) from the plate and on downstream side it (Vena contracta) is at a distance of ½ D. Hence it is also known as D & D/2 taps.