Apparatus for recording and limiting torque

Apparatus for limiting the torque applied to a pipe by a set of power tongs wherein said tongs are operated by hydraulic fluid pumped through a feed line to a hydraulic motor in said tongs and returned by a return line, which comprises:

• a hydraulic tension cell attached to said tongs and secured to a permanent attachment, whereby torque applied by said tongs causes hydraulic pressure in said hydraulic tension cell;
• a helical pressure sensor tube hydraulically connected to said hydraulic tension cell;
• an operating arm attached to said pressure sensor tube such that said hydraulic pressure causes said operating arm to rotate;
• a spring arm, cammingly engaged with said operating arm;
• an air valve, said air valve having a valve member engaged with said spring arm such that when said pressure in said pressure sensor tube causes said operating arm to rotate, said operating arm cams said spring arm to close said air valve;
• an air line supplying air to said air valve;
• a normally closed first diaphragm operated valve in said air line downstream from said air valve, said first diaphragm operated valve being operated by said air valve such that when said air valve closes, said first diaphragm operated valve opens;
• a normally closed second diaphragm operated valve connected between said feed line and said return line and operated by said air line such that when said first diaphragm operated valve opens said second diaphragm operated valve opens to shunt hydraulic fluid between said feed line and return line thereby bypassing said motor.