Quarter circle orifice plate, originally called quarter circle Koennecke nozzle, is a combination of centric orifice plate and ISA 1932 nozzle, entrance to measuring opening of orifice plate is rounded, in the shape of quarter circle. It exists in three options, in which it depends on the relationship between radius of entry rounding r and construction width E of the quarter circle orifice plate and on the difference between diameter of pipe D and diameter of the quarter circle orifice plate d.

Most often this orifice plate is incorporated in the flange joint. Except for CSN standards, sealing surfaces of the orifice plates can be manufactured in compliance with EN, DIN, GOST and American ASME and ANSI standards or, on request and specification of the customer.

ISO 5167-2 and ISO/TR15377 standards define possibility to use quarter circle orifice plate for diameters up to 500 mm. Quarter circle orifice plate is manufactured in nominal diameters ranging from DN 15 up to DN 500 and, similarly to the centric orifice plate, it can be made in design with chamber or individual tapping. Usual construction width of the orifice plate with chamber tapping is 60 mm; usual construction width of the orifice plate with individual tapping is 40 mm. For pipelines with diameter 40 mm and higher the quarter circle orifice plate is manufactured also as an individual disc designed for placement between flanges with a flange tapping.

The orifice plate can be also manufactured in so-called weld-in design. It contains straight lengths of piping downstream the disc. Placement into pipe by welding has the advantages such as material savings on flanges and subsequently minimized leakage in the flanged joint. Weld-in design of the orifice plates is especially convenient for high-pressure parts of piping systems and distribution or, in piping systems requiring seismic resistance.

Upon agreement with customers, outlets of differential pressure are always customized to various options of primary element attachment to the measuring circuit.

For the production of flanges for orifice plates with chamber tapping there is mostly used carbon steel or stainless steel; the disc is made of stainless steel. For the production of orifice plate with individual tapping, there is mostly used refractory alloyed steel or stainless steel. Upon agreement quarter circle orifice plate with both chamber and individual tapping can be made of special materials based on nickel titanium alloy or, tantalum, orifice plates are made of plastic materials, too.

Quarter-circle orifice plate is manufactured as a working meter.

Quarter-circle orifice plate is used for the measurement of viscous fluid flow (e.g. oils) and in operating modes with low Reynolds numbers. Its advantage lies in construction simplicity similarly to centric orifice plates. Quarter circle orifice plate can be incorporated both in vertical and horizontal piping.