Many applications require precise pressure control for a process that is relative to a different pressure in that same process – in other words, differential pressure control. In this schematic, two Proportion-Air QPVs work in tandem to dispense a combination of a sample and a solution. This is differential dispensing.

A counting sensor gathers information at the point of dispensing and sends this information to the PLC. The PLC calculates the command signal supplied to both QPVs. The QPV controlling pressure over the sample is calibrated 0-30 PSI. The QPV controlling pressure over the solution is calibrated -1 to +1 PSI, with the intention of constantly maintaining a specific differential pressure of solution to sample.

QPVs (when calibrated to gauge reference) come standard with an atmospheric reference port. This is the “zero,” or atmosphere point, from where pressure is referenced. The solution-dispensing QPV has its atmospheric reference port tied to the output of the sample-dispensing QPV. This means that the solution-dispensing QPV uses the pressure controlled by the sample-dispensing QPV as its baseline.

Differential dispensing and differential pressure control can be complex. We can help you find a solution that will work for your application.

What is differential pressure control?