You use the Manual Loader function block in applications where an operator adjusts the process input manually (that is, no automatic control) and you want a measurement or calculated value related to this adjustment to be available for display or alarming.
Application example: Manual valve adjustment
When the upstream and downstream operating conditions are constant, the flow through a regulating valve is relatively constant. For such cases, if the flow rate occasionally is set by an operator, the valve can be positioned manually using an indication of the flow rate (such as flow rate, downstream pressure, or other indication). Alarming on this indication might be important to alert the operator that the operating condition has changed. The following figure shows the function block diagram for this example:
