# Auto-Sizing a Differential Pressure Controller

From v3.31 onwards, FluidFlow includes a powerful Auto-Size feature which allows engineers to automatically size a range of elements including differential pressure controllers (DPC). This series of examples demonstrates how a DPC can be automatically sized. To begin, a standard 2 inch DPC with an Exit Static Pressure set point of 1.05 atm has been modeled in a 10.0 M long 2 inch Schedule 40 steel pipeline. This allows us to establish the flow rate, pressure loss and Cv for this size of element in this system. We can then benchmark our automatically sized element against this base model. Figure 1 shows the data entry for the 2 inch DPC and Figure 2 gives an overview of the performance of this device in this system. Figure 1: Data entry for 2" Differential Pressure Controller (Auto Size function set to Off). Figure 2: 2" Differential Pressure Controller Model (Auto Size function set to Off). We can see in Figure 2 that the calculated Cv is 88.9 usgpm/psi, the friction loss is 10264 Pa and the mass flow rate has been calculated as 6.84 kg/s. Auto-Sizing Differential Pressure Controllers. Set the Automatically Size field for the controller to "On" and enter a design Exit Static Pressure of 1.05 atm. Note, the field titled Valve Model has now been removed from the Input Editor. The Input Editor for the controller should now appear as shown in Figure 3. Figure 3: Data entry for Auto-Sizing a 2" Differential Pressure Controller. Figure 4 shows the calculated results for the controller. As we can see, FluidFlow has established a Cv of 88.9 usgpm/psi, a friction loss of 10264 Pa and a mass flow rate of 6.84 kg/s, i.e., exactly matching the results from Figure 2. The element has therefore been automatically sized successfully. We can now select a suitable valve model from the database (2" butterfly valve) or request a proposal from a vendor. Figure 4: Auto-Sizing a 2" Differential Pressure Controller. For further information, a detailed example of automatically sizing components is available at: Design Examples | Auto Equipment Sizing.