is a controller that helps in stabilising the demand side pressure at a constant level, so that it can be optimised to the lowest possible point of operation thereby reducing the air flow (demand). The reduction in air demand is achieved due to reducing or eliminating the artificial demand in the system. This decreased demand on Compressors reduces their load period and thereby saves energy to improve the system efficiency.
The early forms of ‘Flow Controller’ or ‘Pressure Flow Controller’, used a pneumatic regulator in the pilot airline to balance the air pressure on the diaphragm operated valves to provide stable output pressure.
In their new form, ‘Flow Controller’ or ‘Pressure Flow Controller’ uses single or multi-parallel control valves, pressure sensors on inlet & outlet headers and a microprocessor or PLC based controller. The arrangement uses controlled release of air already available in the upstream side storage to stabilize the air pressure delivered into the main piping header. Pressure at control valve outlet is sensed and air flow is continuously adjusted by modulating the control valve/s to correct the deviations from set point. It works on the principle that when compressed air expands, the pressure decreases and, conversely, when air compresses, the pressure increases. Therefore, if more air is flowing out from the balance point than in, the pressure goes down and the control valve/s proportionately open to release more air from storage to bring it back to the set point. The opposite action occurs if more air is flowing into the balance point than away as the valve modulates closed to hold air back in storage.
The new age Flow Controllers not just operate on the PID control, but also utilise many features of the HMI, touch screen, graphics, IoT, data logging, and communication to a remote monitoring system.
This helps in isolating the supply side from demand side, thereby minimising the impact of pressure fluctuations due to sudden variations in the air demand.
Typical schematic layout of compressed air system with Flow / Pressure Controllers for each zone can be set as per desired different pressure requirements:
The Flow Controller is useful in reducing the artificial demand in a system by precisely supplying only the required amount of air flow to maintain a constant air pressure. It is important to decide the lowest operating pressure point without affecting the production and the Flow / Pressure Controller can be set to supply precisely at the desired pressure level, thereby optimising the flow to the demand side.
Pressure Chart: Without Flow Controller (Supply and Demand Pressures – Black & Red lines)
Pressure Chart: With Flow Controller (Supply and Demand Pressures – Black & Red lines)
Flow controllers work with all types of compressors. A VSD compressor despite providing stable pressure at the generation, the pressure fluctuates at the end-use pneumatic applications and a Flow Controller helps there too.
Since uninterrupted air supply to manufacturing process is the priority for reliable operation of any controlling or energy saving system, the current versions of the Flow Controllers are also designed accordingly. The control valves are ‘fail to open’ and some manufacturers additionally provide automatic bypass valve operated by pneumatic or electric actuator. However, while providing the advantage of uninterrupted air supply to the plant, the Flow Controller may remain in bypassed condition if not attended to.
Also, it is likely that the reason for failure or bypassing of the Flow Controller is lack of understanding. Hence if The Flow Controller can be returned into service, it can restart providing the benefits.
Hence it is important to connect the Flow Controllers to a permanent monitoring system to continuously track their performance.