Methods and apparatus to partial stroke test valves using pressure control

A valve positioner comprising:

• a travel controller to:
• define a target travel position for a first valve coupled to the valve positioner via an actuator;
• and
• monitor a position of the first valve;
• a pressure controller including a fluidly-actuated second valve to:
• control, during a partial stroke test, an output pressure of the positioner towards a first pressure set point to actuate the first valve towards the target travel position as the output pressure is controlled towards the first pressure set point;
• and
• control, during the partial stroke test, the output pressure of the positioner towards a second pressure set point after the position of the first valve reaches the target travel position, the second pressure set point to actuate the first valve towards an initial position of the first valve associated with the position of the first valve before the partial stroke test;
• and
• a limiter to define a pressure threshold associated with the second pressure set point and to define a threshold displacement of the first valve from the initial position, the pressure controller to generate an alert indicating that the first valve is stuck if the output pressure passes the pressure threshold associated with the second pressure set point while the position of the first valve is outside the threshold displacement from the initial position.

A tangible computer readable storage medium comprising instructions that, when executed, cause a machine to at least:

• generate a first pressure set point for a valve positioner coupled to an actuator to actuate a first valve, the valve positioner including a fluidly-actuated second valve;
• control, with the fluidly-actuated second valve, an output pressure of the positioner towards the first pressure set point to actuate the first valve in a stroke direction;
• define a target travel position associated with a partial stroke test of the first valve;
• measure a position of the first valve;
• generate a second pressure set point after the position of the first valve reaches the target travel position to actuate the first valve in a return direction towards an initial position of the first valve associated with the position of the first valve before the partial stroke test;
• control, with the fluidly-actuated second valve, the output pressure of the positioner towards the second pressure set point;
• define a pressure threshold associated with the second pressure set point;
• define a threshold displacement of the first valve from the initial position;
• and
• determine that the first valve is stuck while controlling the first valve in the return direction if the output pressure passes the pressure threshold associated with the second pressure set point while the position of the first valve is outside the threshold displacement from the initial position.