TABLE OF CONTENTS This appendix derives the equations used for presenting the graphs for installed valve characteristics for linear and equal percentage valves, Figures 3-6 and 3-7. We will use the following symbols:
| C V | Valve coefficient | |
| C L | An index of the resistance to flow offered by the line and fittings, plus the internal friction of the pump. | |
| C E | An equivalent index, analogous to C V, representing the combined effects of C V and C L | |
| F | Flow rate, gallons per minute | |
| m | Valve position, percent open | |
| R | Valve rangeability ( R = 50 used for Figures 3-6 and 3-7). | |
| ? | Ratio of minimum to maximum pressure drop across valve | |
| ? P V | Valve pressure drop, psi | |
| ? P L | Dynamic pressure drop loss due to pipe friction and internal pump friction | |
| ? P T | Available system pressure drop, psi | |
| ? | Fluid specific gravity. |
An idealized model for a valve installation is shown in Figure B-1. Here the following assumptions are made:
The supply pressure (blocked discharge pressure of pump) and discharge pressure are constant. The difference, ? P T, represents a constant available system pressure drop.
The pressure drop due to internal friction loss in the pump and the pressure drop due to friction loss through the pipe and fittings can be combined into a single pressure drop, ? P L. This pressure drop varies with flow.
The pressure drop through the valve, ?
