There are many applications where a mass flow controller (MFC) isn’t practical. The media may have aggressive or corrosive chemistry or the pressure ranges may be too high. This demonstration of mass flow control at Equilibar’s laboratory in Fletcher North Carolina shows how a back pressure regulator can be used to control mass flow rates of various media. A pressure reducing regulator (PRR) is used to set a fixed pressure to an orifice. This also sets the density at a fixed value if a compressible gas is being controlled. The orifice may be fixed but is often a variable orifice in applications where wide flow ranges are required. A control valve (example Badger Meter Research Control Valve) might be used here to give a controllable orifice. The Equilibar back pressure regulator (BPR) is used to control the output pressure of the orifice. Between the PRR and the BPR the differential pressure across the orifice is effectively controlled. The laws of physics dictate that differential pressure across an orifice controls the mass flow rate of the media. The nature of the back pressure regulator is to automatically vary its internal orifice to keep the pressure at set point. Changing restrictions farther downstream in the system are automatically compensated for by the normal mechanical workings of the back pressure regulator. In our experiment, the mass flow rate was shown on a Teledyne Hastings mass flow transducer.