Meaning
Resistive torque profile generated during the central portion of a valve stroke. Measured in Newton meters or foot pounds, running torque accounts for the friction between the stem and the packing as well as the contact between the closure element and the seals. It remains lower than the breakaway torque but constitutes the primary load during the middle portion of the stroke.
Actuation Sizing
Motorized operators must provide sufficient output to exceed the maximum running torque across the entire travel. If the power supply drops or the fluid viscosity increases, the running torque may rise and stall the motor. Engineers size the gearbox to handle these sustained loads without overheating the drive components.
Process Influence
Media properties such as density and the presence of solids significantly alter the resistive force of the internal parts. High velocity flow can create a dynamic imbalance that increases the running torque as the valve nears the closed position. Slurries create a grinding effect on the seats that raises the power requirement compared to clean water service.
Operational Efficiency
Minimizing friction through surface polishing and the use of high quality lubricants reduces the energy needed for each cycle. A lower running torque allows for the selection of smaller, less expensive actuators and reduces the wear on the internal drive train. Regular maintenance of the stem packing ensures that the resistance remains within the original design parameters.
