Abstract: Fluid flow measuring apparatus comprising first and second pipe portions, a housing positioned around the pipe portions, a chamber in the housing, an orifice plate, an orifice plate moving device for moving the orifice plate from a first position in which it is located between the pipe portions to a second position in which it is located in the chamber in the housing and for moving the orifice plate from the second position to the first position, and a sleeve seal for sealing the pipe portions when the orifice plate is in the second position, the housing being fabricated of metal in sheet and/or tubular form, the housing having a pivotable lid, and the orifice plate moving device being such that it can be pivotted to an inoperative position for allowing access to the orifice plate.