It is important first to determine if you require preload. Preload is used when you expect to be shutting all or part of the sliding core face off on an opposing core face in the mold. This is done when you form a "Window" in your molded part and you must prevent flash in front of the sliding core face. Recommended preload is given in the packing slip as well as in the DME catalog for each size of HLCP cylinder. Please note that when preload is used, the net load capacity of the cylinder is reduced.
When determining the required load capacity, it is good practice to consider the entire face of the sliding core, even the portion that will be under preload. This total area should be multiplied by the peak injection pressure expected to be seen inside the molded part cavity. If you are uncertain as to what the peak injection pressure might be, a mold filling analysis can assist you, or, consider the peak injection pressure offered by the injection machine in total. It is good practice to select a cylinder load capacity (a cylinder size) that exceeds by a sufficient margin, the estimated load that expected to be acting on the piston rod.