Linear Characteristic
It is the curve in which flow rate increases at a constant ratio with the control signal: half the lever travel gives half the flow. Its greatest advantage is predictability; it lets the operator build a single mental mapping between speed and lever angle, and it simplifies automation calculations.
A linear curve assigns an equal amount of flow rate to every millimeter of lever travel. This is an advantage in jobs where speed must be held roughly constant: running a long boom movement at an even speed, or turning a conveyor at a given speed.
- Suitable jobs: constant speed feeding, repeated cycles, the inner loop of closed loop position control.
- Where it falls short: jobs that demand both very slow placement and high peak speed. With a linear curve you cannot do both well at the same time.
- A linear valve is preferred when designing a closed loop controller because the gain does not change with the operating point.
In practice many machines offer both characteristics and leave the choice to the job. The Soft and Dynamic mode options in AXI's HCT402 kit answer the same need; the mode is changed by connecting the blue wire going to the motor body to negative.
Where this term is used: The Importance of Hydraulic Control: Why Should It Be Commanded by an Electronic Signal?