The investigation of valve operators' torque production capabilities and optimal handwheel height, angle, and opening technique
This research consists of two projects concerned with handwheel-valve operations. The objectives of poject-1 were to: (1) introduce an ergonomically-modified valve-wrench and compare it to conventional valve-opening methods, in terms of efficiency (time to open valve), perceived physical exertion (Borg-scale), and muscle loading of shoulder and trunk muscles; and (2) determine whether the torque setting (15 Nm and 30 Nm) of the valve affects the preferred valve-opening method. Four methods were evaluated, including using bare hands (BH), conventional wrench-restricted (CW-R, assumes presence of obstructions), conventional wrench-unrestricted (CW-U, assumes no obstructions), and modified wrench (MW). Electromyography (EMG) activities were measured from the right and left anterior deltoids, trapezii, latissimi dorsi, and erector spinae muscles. The EMG activity of each muscle was normalized to the maximum EMG activity of the corresponding muscle’s reference contraction (RC). This study used new RC procedures for the anterior deltoids and trapezii that were associated with higher EMG amplitudes than the RC procedures found in the literature. The valve-opening method that was associated with the lowest overall EMG activities was CW-R, followed by BH, MW, and finally CW-U. According to the time recordings and Borg-ratings, the MW was the most efficient and least physically demanding method in opening the valve. The objectives of project-2 were to: (1) investigate operators’ torque production capabilities and recommend maximum torque limits for different handwheel heights (knee, elbow, shoulder, and overhead levels) and angles (0o, 45o, and 90o); and (2) determine an optimal handwheel height and angle, in terms of operators’ maximum isometric torque exertions and the EMG activities of the same shoulder and trunk muscles as in project-1. The average maximum torque exertions ranged between 51.6 Nm (at overhead 0o) and 74.9 Nm (at overhead 45o) depending on the height and angle of the handwheel. Through calculating the 5th percentile torque strength values of the female participants, this study recommends maximum torque limits ranging between 13.7 Nm and 24.1 Nm, depending on the height and angle of the handwheel. Analysis of the results indicates that the optimum height and angle of a handwheel is at shoulder level and zero degree.
handwheel, valve, torque production, valve-wrench, valve-operations, MVC, EMG, torque exertion
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Engineering Science (Interdepartmental Program)