Patent ID: 8037786

Claim:
A hydraulic system for activating at least one hydraulically actuated clamping die of a power tong, said hydraulic circuit comprising: a power tong, at least one clamping die, a hydraulic cylinder pump, an accumulator, a first check valve, at least one clamping die cylinder, a volume cylinder and an activating valve; wherein said power tong having two housing halves, pivotable relative to each other, and a radially divided drive ring having a first drive ring part and a second drive ring part, said housing halves being arranged to be pivoted between a closed, active position and an open, inactive position, said drive ring being located in said housing halves and supported and connected to at least one driving motor for the rotation of said drive ring about a centre axis and having one of said at least one hydraulically activated clamping die directed toward said centre axis, said hydraulic pump cylinder being articulatedly connected between said first drive ring part and said second drive ring part and arranged to rotate with said drive ring about said centre axis; wherein, said hydraulic pump cylinder being in communication with said accumulator via said first check valve, said accumulator being in communication with said clamping die cylinder through said activating valve; and a volume cylinder; and wherein a hydraulic fluid flowing from said clamping die cylinder is directed into said volume cylinder, said volume cylinder being limited in volume and sized to receive an effective amount of hydraulic fluid for the purpose of withdrawing said clamping die a desired distance.