Pressure independent, sometimes referred to as automatic, balancing valves are the next step in the evolution of simplified sizing and selection.
PIBV valves are also sometimes called “automatic” or “dynamic” balancing valves. They are designed to maintain a constant preset flow rate, even when the differential pressure across the valves varies over a wide range. They rely on an internal compensating mechanism to adjust an orifice within the valve so that a calibrated flow rate is maintained within a listed tolerance, typically +/- 10% of the calibrated flow rating. Figure 4-1a shows one body style used for PIBVs.
The internal components in a pressure-independent balancing valve consist of a cylinder, a spring-loaded piston, and a combination of fixed and variable-shaped orifices through which flow passes. The assembly of these components is called the “cartridge” of the PIBV. An example of such a cartridge is seen in Figure 4-1b.
A Y-pattern PIBV is shown in Figure 4-2a. It uses the same type of pressure-regulating cartridge as the valve shown in Figure 4-1a. The Y-pattern valve also allows installers to easily change the cartridge if the design flow rate specification changes. The cartridge can also be removed when the system is being flushed, and then reinstalled.
One example would be a replacement scenario for a hydronic fan coil, wherein the unit being replaced required 2 gpm, but the new unit only requires 1 gpm. Another example would be if panel radiators were retrofitted into a branch circuit to provide heat for a building addition. The original branch flow rate of 2 gpm might not be sufficient, so it could be replaced with a cartridge having a higher flow rate calibration.
The flow cartridge within a PIBV is composed of a cylinder, a spring-loaded piston, and a combination of fixed and variable geometric orifices through which the fluid flows. These variable orifice sizes increase or decrease by the piston movement, contingent on the system's fluid thrust. A specially calibrated spring counteracts this movement to regulate the amount of fluid that will pass through the valve orifices, maintaining a constant flow rate in the circuit.