In a parallel installation for a modulating load, which valve is set to the higher pressure?

In a parallel installation for a modulating load, the choice of setting the smaller capacity valve to a pressure that is 2 psig over the operating set point is important for maintaining system performance and efficiency. This approach ensures that the smaller valve can effectively handle the modulating demands by providing a higher differential pressure when required.

When a modulating load is present, particularly in systems where multiple valves manage the flow simultaneously, the smaller valve needs an adequate pressure setting to open fully and to modulate effectively according to the system's variable demands. Setting this valve at a pressure slightly above the operating point allows it to respond to changes in load, enabling better control and reducing the chance of flow oscillations that could lead to instability in the system.

Meanwhile, larger capacity valves often operate at pressures closer to the main system pressure, but the differentiation in settings between larger and smaller valves becomes crucial for load modulation. Therefore, this choice emphasizes an effective strategy for managing different valve capacities within the system while ensuring responsiveness to modulating loads.