Power tongs and control system

Abstract

A control system for power tongs comprises two tongs torque limiters, one of which limits tongs torque to a very low (hand-tight) level; the other limits torque at full makeup to, for example, 2000 ft. lb. The hand-tight torque limiter is manually or automatically disabled after the hand-tight level is reached. The system enables the operator to verify that the threads are properly engaged before applying full torque to the connection. The tongs have a very high reduction ratio, so that torque rises very slowly and can be more accurately controlled.

I claim: 
     
       1. A control system for a power tongs comprising a snub line for restraining the tongs, a first snub line tension transducer for generating signals proportional to tongs torque in the hand-tight range,   a second snub line tension transducer for generating signals proportional to tongs torque in the full makeup torque range,   first means responsive to said first transducer for halting tongs operation at a preset hand-tight torque level,   second means responsive to said second transducer for halting tongs operation at a preset full makeup torque level, and   means for disabling said first means.   
     
     
       2. The system described in claim 1 wherein said tongs have high and low speeds and a gear selector for choosing between said speeds, and said disabling means is controlled by said gear selector.   
     
     
       3. The system described in claim 2 wherein said disabling means is actuated to disable said first means only when the tongs are operated in the lower of said two speeds. 
     
     
       4. The system described in claim 3 wherein the ratio between said high and low speeds is at least 4:1. 
     
     
       5. The system described in claim 4 wherein the overall gear ratio between the tongs motor and the tongs jaws is about 250:1 in low speed and about 60:1 in high speed. .Iadd. 
     
     
       6.  A control system for a power tongs comprising means for restraining the tongs from rotation,   a first transducer operatively connected to said restraining means for generating signals proportional to tongs torque in the hand-tight range,   a second transducer operatively connected to said restraining means for generating signals proportional to tongs torque in the full makeup torque range,   first means responsive to said first transducer for halting tongs operation at a preset hand-tight torque level,   second means responsive to said second transducer for halting tongs operation at a preset full makeup torque level, and   means for disabling said first means..Iaddend.