The orifice meter is the most commonly used differential measurement device used in measuring the volumes of natural gas or liquid streams. The orifice meter consists of static pressure and differential pressure recording gauges connected to an orifice fitting or flange. The meter run has upstream and downstream sections of pipe, which are sized for accurate flow measurement. A properly sized meter tube and orifice plate will provide flow measurement accuracy within plus or minus 2 %.

Measurement records are maintained through the installation of recorders. A circular chart recorder uses a round chart along with a marking device to record the differential pressure within a specified period of time. The temperature can also be recorded with the use of a three-pen recorder that will mark temperature readings on the same chart.

Orifice fittings and meter tubes are available in various sizes, pressure ratings, and end connections. United Process Systems & Supply can provide differential products that meet all requirements and recommendations for accurate flow measurement of liquid and gas in AGA.3 and Daniel 4^th Edition April 2000 version of AGA.3 (API14.3)

Part II specification.