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
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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.
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