1.What medium (fluid) do you want to control?
With regard to its chemical-physical reaction behaviour, it must be checked whether the valve parts in contact with the medium are compatible with the medium itself.
- How high is the maximum operating pressure?
The valve must be able to shut off the highest pressure in the application.
3.What are the process data?
For optimal sizing of the valve orifice there are some issues to be cleared up. At first there is the scope of the required maximum flow rate, Qnom, which typically has to be controlled. The valve’s maximum flow rate can, however, actually be higher, and the figures of the pressure values at Qnom must be measured immediately before and after the valve (p1, p2). These values are often not identical to the inlet and outlet pressure of the overall system, because additional flow resistances have an effect both before and after the valve (pipes, shut-off valves, nozzles, etc.).
If the inlet (p1) and outlet pressure (p2) cannot be determined, both must be estimated taking all pressure drops into account. Information on the medium temperature (T1) and the standard density (pN) of the medium at 273 Kelvin (0 °C) and 1013 mbar (1 bar) also helps in calculating the valve orifice. Whether or not the minimum flow rate can be adjusted (Qmin) is checked using the achievable turn-down ratio of the valve considered.