The torque of a hydraulic
wrench does not start from 0, it is also determined by a special pump for a hydraulic
wrench. Because the hydraulic
wrench pump is a two-stage pump or a three-stage pump, whether it is a gear pump or a plunger pump at low pressure and large flow, the overflow is large, the pressure is unstable, and the output torque of the wrench is also unstable. Accurate torque measurement starts from the second stage, the second stage flow is much smaller than the low pressure flow, there is no overflow, stable, the torque can be accurately controlled.