70 is provided mounted in a hole 71 in the handle body 14 and in fluid flow communication with the inlet and outlet to regulate the oil pressure in the tool in a manner well known in the art referring to fig2 7 and 8 the knob assembly is shown in greater detail the knob 9 is mounted to the spool 13 by a roll pin 90 the handle assembly body 14 has a step 93 that extends for more than 180 degrees the roll pin 90 is restrained by the step 93 and the head of a mushroom shaped pin 91 mounted in the handle assembly body 14 this prevents the spool 13 from rotating by itself to turn the knob 9 the operator of the device must depress the trigger 10 all the way in which event the roll pin 90 will be positioned to clear the head of the mushroom pin 91 upon rotation of the knob 9 the knob can then be rotated 180 degrees from the u201c open center u201d position shown in fig7 to the u201c closed center u201d position to provide the operator with an indication of the operating condition of the device i have provided indicia.