Answer / carl_ellis

A bubbler system uses a pneumatic differential relay as a constant flow regulator.  Most bubbler systems include a variable area flowmeter, a rotameter, to indicate the air/gas flow rate and a needle valve for adjusting the flowrate.  

Typical air/gas flowrates for bubblers are 8-30 cc/s (1 to 4 SCFH), a flow rate suitable to create a constant stream of bubbles from the dip tube.

The only 'calibration' of the pressure transmitter in a bubbler system is setting the range of the transmitter's 4-20mA output with a zero-to-span range that takes into account the maximum liquid column head pressure that the transmitter will 'see', which takes into account the specific gravity of the liquid.

Conversion to physical level units (accounting for specific gravity) is done in the receiver (indicator/PLC/DCS/PAC/controller).

Carl Ellis
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