Water flow meters that use an inferential method of flow measurement can use a simple formula or correction factor (K factor) since it is known that there are not going to be great enough changes in the flow profile in good flow conditions . However this may not be true in very large pipes where in house initial flow calibration for those sizes has never been possible.
Averaging pitot tube flowmeters will normally depend upon modern day differential pressure transmitters to do the calculations. They can also be supplied with options such as temperature inputs.
These DP transmitters are standard products which have built in calculations for a myriad of pressure based flow measurement. Coupled to 3 way manifold valves, the user has the option to isolate, equalize and vent pressure.
The averaging pitot can be found in various steam, liquid and gas applications. They offer better accuracy than a standard pitot static tube for small and large size pipes and even rectangular or square ducts.
Some of them are designed to be able to hot tap into pressurized pipes and others can be designed for auto insertion ( installed and removed under full pipeline pressure) which has great advantages to those who want to inspect the mechanical tube as part of preventative maintenance or retract the device during a pigging operation.