Once the breakaway torque is determined, the next step is applying a safety factor. Some valve suppliers will give the torque rating with a safety factor already included for the application. However, unless clearly stated, end users and installers should never assume that the safety factor is included. In other instances, vendors may supply a safety factor chart as a reference to be used with the stated valve torques.
If neither of these options are supplied by the manufacturer, then the following safety factors may be used as guidelines:
Type of media
Wet or lubricating applications — 20 percent
Dry gas or steam applications — 30 percent
Viscous or abrasive applications — 50 percent
Type of operation
On/Off applications — no additional factor
Proportional applications — 20 percent
Frequency of operation
Daily — no additional factor
Weekly — 30 percent
Monthly — 50 percent
By selecting the appropriate factor from each step and adding them together, a cumulative safety factor can be applied to the breakaway torque.
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