SMART Positioners VALVE maximum differential pressures
The thrust available to close the valve has to provide three functions:
1. To overcome the fluid differential pressure at the closed position.
2. To overcome friction in the valve and actuator, primarily at the valve and actuator stem seals.
3. To provide a sealing load between the valve plug and valve seat to ensure the required degree of tightness.
Control valve manufacturers will normally provide full details of the maximum differential pressures against which their various valve and actuator/spring combinations will operate; the Table in Figure 6.6.10 is an example of this data.
Note: When using a positioner, it is necessary to refer to the manufacturer’s literature for the minimum and maximum air pressures.
Fig. 6.6.9 Two and three port formulae Fig. 6.6.9 Two and three port formulae
6.6.10 Typical manufacturer’s valve/actuator selection chart
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