Control valve positioners (“positioning controllers”): identify the typical application context where a valve positioner is preferred for reliable stem positioning.

Introduction / Context:
A control valve positioner compares the controller’s output signal with the actual stem position and boosts actuator pressure/force to eliminate positioning error. It is commonly installed where direct I/P (current-to-pressure) action cannot overcome friction, unbalanced forces, or hysteresis.

Given Data / Assumptions:

• Pneumatic or electro-pneumatic actuators are used.
• Mechanical linkages may introduce backlash and friction.
• Process conditions can create large unbalanced torques/forces.

Concept / Approach:
Positioners amplify the control signal locally at the valve, increasing stiffness and reducing dead band. They are particularly valuable for high-load applications: large valves, high differential pressures, sticky packing, long strokes, or fast response requirements. In light-load systems, direct I/P may suffice and a positioner may be unnecessary.

Step-by-Step Solution:

Verification / Alternative check:
Valve vendor guidelines recommend positioners for valves with high shutoff differentials, large diameters, or where stroking speed and accuracy must be ensured.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming positioners are only for split-range or cascaded loops; their primary role is accurate positioning under demanding mechanical loads.

Final Answer:
High loads (large actuators, high friction or long strokes)