JUNE-JULY 2018 Nov-Dec 2017 - Copy - Page 86

BOOK IN SERIES Linear Resistances in Parallel: Figure 1.9 shows three electrical resistors in parallel and three hydraulic lines in parallel. Equations 1.7 and 1.8 show how to calculate the equivalent resistance in both cases. The calculation in both cases is based on the following two facts:  The effort variable across the resistive elements in parallel is the same.  The total flow variable equals the sum of the flow variables through each element in parallel.  ∆ ∆ ∆ ∆      ⇒   .                            ∆ ∆ ∆ ∆                  ⇒   .               Fig. 1.9 - Linear Resistances in Parallel 86 Nonlinear Hydraulic Resistances: When a hydraulic valve performs its control function, fluid flow through the valve is accompanied by a pressure drop. Valve manufacturers express the resistivity of a hydraulic valve by a term called Valve Coefficient. Equation 1.9 shows the nonlinearity between the differential pressure ∆ p across the valve and the flow rate Q of hydraulic fluid that has a specific gravity SG. A large valve coefficient means the valve passes a large flow for small pressure drop. www.ghmediabusiness.com