Control valve characteristic guidelines
 


Constant delta pressure 

Decreasing delta pressure with increasing load, delta pressure at maximum load > 20% of minimum load delta pressure. 

Decreasing delta pressure with increasing load, delta pressure at maximum load & 20% of minimum load delta pressure. 

Increasing delta pressure with increasing load, delta pressure at maximum load & 200% of minimum load delta pressure. 

Increasing delta pressure with increasing load, delta pressure at maximum load > 200% of minimum load delta pressure. 

Source: Control Engineering with data from Fisher Controls 
 
 
Flow measurement signal to controller is:  Location of control valve in relation to measuring element is:  Wide range of flow setpoint  Small range of flow but large delta pressure change at valve with increasing load 
Proportional to flow  In series  Linear  Equal percentage 
In bypass *  Linear  Equal percentage  
Proportional to flow squared  In series  Linear  Equal percentage 
In bypass *  Equal percentage  Equal percentage  
* When control valve closes, flow rate increases in measuring element. 
 


Liquid process 

Gas process, small volume, less than 10 ft (3 m) of pipe between control valve and load. 

Gas process, large volume [process has a receiver, distribution system, or transmission line exceeding 100 ft (30.5 m) of nominal pipe volume], decreasing delta pressure with increasing load, delta pressure at maximum load >20% of minimum load delta pressure. 

Gas process, large volume, decreasing delta pressure with increasing load, delta pressure at maximum load &20% of minimum load delta pressure. 

Source: Control Engineering with data from Fisher Controls 
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