One key challenge in product filling machines is to handle the rapid change in flow rate during the start-up and shut down of a filling line. For example, if a filling line has 20 parallel nozzles, it might take several seconds during machine start-up for each of the positions to become active as empty containers gradually begin advancing through the machine. The opposite situation occurs at machine shut-down as the last container works its way through the positions. During these ramps up and down, the header flow rate can vary dramatically.
Variable frequency pump drives (VFD) are very useful for controlling pressure under varying conditions, but unfortunately require several seconds to change speeds. These VFD drives are not always able to handle all the challenges that are presented by these filling applications.
Other challenges are presented to the process engineer when viscous fluids or non-Newtonian fluids are involved. These systems need to be designed to process high flow rates of Clean-In-Place chemicals as well as relatively lower flow rates of viscous materials.
High Speed Pressure Control for Filling Machines
For challenging filling applications, one solution is to install a high speed back pressure regulator near the exit of the nozzle manifold, as shown in the schematic above.
The primary requirement of this approach is to install a circulation line back to the inlet of the pump. While this is sometimes complicated, the advantages can be significant for applications experiencing persistent pressure fluctuations.
The Equilibar back pressure regulator (BPR) is a high precision device that responds in approximately 1 mS to pressure changes at its inlet. The speed and precision are driven by the use of compressed air as a 1:1 pilot signal on the top of dozens of parallel orifices. (how it works)
If the BPR can be mounted extremely close to the manifold, it may be possible to run with a fixed air pressure pilot. For example, to control the manifold at 2 bar, a 2 bar air signal would be supplied to the dome of the BPR.
However, for many applications, such as viscous fluids or installations where the BPR is not located directly at the manifold, a two-loop electronic pressure controller would be recommended (as shown). This closed-loop approach assures that the manifold pressure sensor sees the desired pressure by making slight adjustments as needed to the pilot pressure on the dome to offset friction effects throughout the system.
Equilibar engineers are highly experienced at designing systems for this type of demanding application. Contact an engineer today to discuss your product filling challenge.