What type of paddle wheel switch are you using? I know of a company that specializes in custom thermal flow measurement. try intekflow.com
Dr. Tim and Dr. Joe
Flow Measurement and Steam Surface Condenser Professionals
As rmw inquired, What is you steam operating pressure at low and high load? If the rated temperature is 900F and you operate at 1005F then the SJAE should operate better at the quoted 930F. Since this is not the observed condition please consider the following.
Air-in-leakage is common at low...