1. Increase
control system resolution: i.e. fine control.
2. Allow use
of characteristic cams.
3. Minimize
packing friction effects: i.e. high-temperature packing.
4. Negate
flow-induced reactions to higher pressure drops.
5. Increase
speed of response to a change in process.
6. Allow split
ranging.
7. Overcome seating friction in rotary valves.
8. Allow distances between controller
and control valve.
9. Allow wide range of flow variation:
i.e. operate at less than 10% travel under
normal conditions.
10. Allow increased usage of 4-20 mA
electronic signal.
11. Increase fast venting (unloading)
capability.
12. Permit use
of piston actuators.
13. Facilitate operation when the higher
number in the bench-set range is greater than
15 psig: i.e. 10-30 psig, 6-30 psig, etc.
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