The LMI pumps are Diaphragm type pumps. The diaphragm is driven by a solenoid atached to its center. The mechanical stress can become quite high.
For high pressure applications you should consider Hydraulic Diaphragm pumps (DOSAPRO Milton Roy, the owner of LMI, has this kind of products)...
We don't find ORP usefull for chlorine control. The ORP is a non-linear function of pH and Chlorine (and, off course, is also affected by other dissolved chemicals).
We find it acceptable for two uses: a) as a cheap device for detecting the presence of low levels of chlorine. b) as a cheap...