Municipalities and the like have extensive networks of piping to control the flow of water from storage and pumping stations to users. The network of piping includes numerous valves such that portions of the network can be closed off as needed for service while the remainder of the network remains in operation. The piping required for such networks can range from as small as three or four inches in diameter to as much as three feet in diameter. Also, the valves of the system typically remain in an open position or a closed position for very long periods of time. In a typical municipal water system, the valves are located below ground with an access shaft extending from the valve stem to the surface through which an elongate key is extended for turning the stem. Such valves typically include a screw rotated by the stem for opening and closing the valve, and the screw often requires 100 rotations of more to fully open or fully close the valve.
Underground valves are usually subjected to moisture and temperature changes, and the parts of the valve undergo certain deterioration over a Long period of time. Where a valve is infrequently operated, it typically becomes frozen, or locked into its current position as a result of the contamination and deterioration occurring in the valve.
Valve operating machines are provided which are generally mounted to a truck or the like and positioned over the shaft leading to a valve. Existing valve operating machines have a hydraulic motor to rotate an elongate key which extends to the stem of the valve. The motors of the machines are hydraulically operated and include sensors for determining the torque applied to the valve stem, and controls whereby a technician can increase or decrease the torque applied. To loosen a frozen valve without causing damage, the technician should apply torque in alternate directions until the valve loosens. When the technician knows whether the operator is to be rotated clockwise or counterclockwise, he will apply the greater amount of torque in the direction in which movement is desired. Once the valve has been broken free, a smaller amount of torque is required to move the valve, unless deposits within the valve become accumulated on the screw or other portions thereof and cause the valve to jam. Where the valve becomes jammed, the technician should turn the valve in the opposite direction for a short distance, typically one revolution, to loosen residue on the parts of the valve. After loosening the residue, the valve is again turned in the desired direction until the valve is either fully opened or fully closed. Existing valve operating machines include counters, and the technician may know that he has reached the opened or closed position for the valve by the number of revolutions that the valve has turned. In other cases, the technician does not know the number of revolutions required to open or close the valve. In such cases the valve will be turned until forward rotation has stopped, and reversing the valve will not result in further forward movement.
Existing valve operating machines are capable of applying a greater amount of torque to the stem of a valve than many valves are able to withstand. The maximum torque limits of each valve is known and an operator should never apply torque which exceeds the limit of the valve. A technician who is experienced, patient and careful, can operate a valve as described above without causing damage. Damage is caused to the valve, however, where a technician expects a valve to move in the wrong direction and applies an excessive amount of torque in the wrong direction. Damage can also occur to a valve when the valve becomes jammed and the technician causes an excessive torque to be applied to the stem rather than reversing the direction thereof as described above. It would, therefore, be desirable to provide a valve operating machine which would overcome the problem caused by impatient and careless technician. Specifically, it would be desirable to have machines which would loosen a frozen valve by gradually applying a greater amount of torque in opposite directions to the valve. It would also be desirable to provide a valve opener which would detect increases in torque requirements characteristic of jamming and automatically reverse the direction of rotation to thereby relieve jamming.