# Auto-Sizing Self-Acting Pressure Sustainers/Reducers

From v3.31 onwards, FluidFlow includes a powerful Auto-Size feature which allows engineers to automatically size a range of elements including self-acting pressure control valves. This series of examples demonstrates how self-acting pressure sustainers can be automatically sized. The same approach can be used to size self-acting pressure reducers. To begin, a standard 2 inch butterfly pressure sustainer with an Entry Static Pressure set point of 1.18 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 valve and Figure 2 gives an overview of the performance of this device in this system. Figure 1: Data entry for 2" Pressure Sustainer (Auto Size function set to Off). Figure 2: 2" Pressure Sustainer Model (Auto Size function set to Off). We can see in Figure 2 that the calculated Cv is 67.9 usgpm/psi, the friction loss is 14105 Pa and the mass flow rate has been calculated as 6.13 kg/s. Auto-Sizing Pressure Sustainers. Set the Automatically Size field for the controller to "On" and enter an Entry Static Pressure of 1.18 atm. Note, the field titled Valve Model has now been removed from the Input Editor. The Input Editor for the sustainer should now appear as shown in Figure 3. Figure 3: Data entry for Auto-Sizing a Pressure Sustainer. Figure 4 shows the calculated results for the sustainer. As we can see, FluidFlow has established a Cv of 67.9 usgpm/psi, a friction loss of 14105 Pa and a mass flow rate of 6.13 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 Pressure Sustainer. For further information, a detailed example of automatically sizing components is available at: Design Examples | Auto Equipment Sizing.