Cox Precision Sonic Nozzles Series 220

The Series 220 sonic nozzles are mass flow instruments designed for the accurate measurement and control of gas flow. The nozzles can handle flow from 0.04 to 10,000 standard cubic feet per minute.
The internal design of the nozzle consists of a circular arc that leads to the minimum throat area. Tangent to the circular arc on the exhaust side is a conical diffuser section. 
Common applications of the sonic nozzle include use as a calibration standard, gas flow meter, flow controller and flow limiting device.
Standard nozzles are sized according to the inlet pressure available to give continuous and overlapping flow ranges. Sizes range from a minimum throat diameter of eleven thousandths of an inch to a maximum of one inch.
These nozzles may be purchased individually or in sets of seven or ten nozzles, that include the upstream and downstream flow straighteners. Taps are provided in the upstream flow straightener for pressure and temperature sensing.
A pressure tap is provided in the downstream flow straightener to check for a critical ratio across the throat. The nozzles, as well as the flow straighteners, are available with AN-8, AN-16 or AN-32 flare tube fittings, and are suitable for use up to 3000 psia inlet pressure. NPT fittings are available upon request.


The sonic nozzle is similar to a subsonic variable head type flowmeter in that a constriction is present in the flowstream.
As the gas flows through the converging section of the nozzle, the inlet pressure is converted to velocity, which reaches a maximum at the throat. When the fluid velocity reaches the speed of sound at the throat, the flow rate varies linearly with the inlet pressure and is not affected by downstream pressure fluctuations. The pressure drop across the nozzle must be sufficient to maintain sonic flow at the throat. Normally, sonic flow occurs when the downstream pressure is not greater than one-half the upstream pressure. The Cox design improves this ratio so that sonic flow can be achieved in many applications when the downstream pressure is as much as  three-quarters of the upstream pressure. The determination of mass flow rate using the sonic nozzle requires only two measurements— the nozzle inlet absolute pressure and the inlet absolute temperature.