We have it on three power units that have pivots with corner systems.  All are slightly different setups but generally are supposed to run at 40 psi.  Without the throttle controller we were upwards of 65 or 70 psi when the system was closed and not needing as much water.  We were told to set the upper and lower PSI limits about 5-7 PSI apart so that the controller didn't regulate too much.  It seems to work well.  I just ran one the past few days and every time I monitored it, it was at 40 PSI.  Prior to this it would vary from 40-55.