The On-Off Perforator allows the operator to run a BHA into a wellbore, circulating without restriction down the tool-string.  When the operator choses to switch pumping operations to the Abrasive Perforator, a drop ball is pumped to the BHA, shifting the flow.  This stops all fluid flow below the Perforator.  Once the abrasive perforating operation is completed, a second drop ball can be deployed to the BHA.  This changes the fluid flow path again, stopping flow to the Abrasive Perforator, back through the tool-string below.

The general use is for Confirmation/Milling runs, where the operator may wish to have the option to cut a perforation interval at the toe of the well, and still have the milling BHA operational while POOH without having to make a second run to TD.