Validity of Isometric Strength Tests for Predicting the Capacity to Crack, Open, and Close Industrial Valves

Abstract

Cracking, opening, and closing valves are physically demanding tasks required of chemical plant process operators. This study determined if isometric strength tests predicted the capacity to: 1) crack valves; and 2) fully open or close them. The study involved three interrelated steps: 1) compete task analyses to define the torque required to crack valves and the total amount of work required to open or close industrial valves; 2) develop valve turning simulation tests; and 3) complete laboratory studies to define the level of isometric strength demanded for valve turning performance. A total of 405 valves at two major chemical plants were measured to find the torque required to crack, open, and close industrial valves. These data were used to develop two job simulation tests, one measured valve cracking capacity, and the second the endurance needed to open or close a valve. An electronic torque wrench measured valve cracking capacity in eight different ways, and a valve turning ergometer measured the subject's endurance to work for 15 minutes at a power output of 1,413.5 foot-pounds/minute. The sum of isometric grip, arm lift, and torso lift strength tests (ɛIS) measured strength. The isometric strength and endurance work valve tests were administered to 26 men and 25 women. The isometric strength and valve cracking tests were administered to a second sample of 118 men and 66 women. The correlations between ɛIS and work test performance were 0.65 and 0.83 for valve cracking and valve endurance tests respectively. Logistic regression models defined the strength level needed to crack valves and completely close valves.