Modern gas mass flow meters typically use the thermal or heat transfer technique for dependable mass flow measurement through flow rate ranges with turn-down ratios of up to 100:1. They depend on constant gas density for accurate calibration. The Equilibar precision back pressure regulator can be used to obtain a stable process pressure through a wide range of flow rates.
In the schematic below, a standard or reference mass flow controller is used to provide a known mass flow rate to the flow instrument to be calibrated. The Equilibar precision back pressure regulator keeps a constant back pressure and therefore gas density on both instruments.
The Equilibar Difference
Typical spring-type back pressure regulators operate through a relatively narrow flow rate range, such as 10:1. Below a certain flow threshold, they cannot hold back target pressure and exhibit “under-pressure”. As the flow rate increases to the upper end of their range, the spring compresses and the inlet pressure increases (“Over pressure”). This under-pressure and over-pressure can cause for a very lengthy mass flow meter or mass flow controller calibration, as the knob must be constantly adjusted to keep your gas at constant density.
The Equilibar dome-loaded back pressure regulator doesn’t use a spring, but rather uses a fluid set-point pressure to ensure constant force loading on its diaphragm (see how it works). Unlike other dome-loaded designs, it has unmatched sensitivity down to the ultra low pressure range. It can save significant time and increase the accuracy of your gas mass flow controller calibration.
Improving Controlling Flow with Mass Flow Controllers
The difference between an MFM (mass flow meter) and a MFC (mass flow controllers) is that an MFC has a flow control valve integrated inside. However, there are many technical limitations of these integrated flow control valves, including differential pressure requirements, and chemical/phase limitations. In many cases, an Equilibar back pressure regulator can be used with a mass flow meter as the active flow control valve for demanding applications.
Contact one of our Applications Engineers to help select the perfect back pressure regulator for your fuel cell application.