OS 81 Positions 1-3: Extension of OS 80
Positions 1-3 of this option switch are not for branches; they are an extension of Option Switch 80: Dimensions (To Valve Centers), whereby dimensioning to the centers of valves and instruments can also be done by bore range. Option Switch 80 controls dimensioning to the centers of valves and instruments by end type.
In the following example, OS 81 Pos 1-3 = 24 and OS 80 Pos 4 = 1, which gives dimensions to the socket weld valve and instrument centerline for all bores up to and including 1-1/2 inches.
In the next example, OS 81 Pos 1-3 = 24 and OS 80 Pos 4 = 1, which gives dimensions to valve ends for 2-inch bore. That is, the valve is outside the bore range set in OS 81, so it does not get center-dimensioned.
OS 81 Positions 4-6 and Positions 7-8: Branch Dimension Function
Branch dimensioning functions are controlled by Option Switch 81 Positions 4, 5 and 6 and Positions 7 and -8. In the following example, OS 81 Pos 4, 5, 6 = Blank and OS 81 Pos 7, 8 = Blank, which gives full branch dimensioning regardless of the branch bore and the number of components in the branch.
In the next example. OS 81 = 48 000, which suppresses branch dimensioning on branch bores of 3-inches or less regardless of the number of components in the branch.
The following example sets OS 81 = 2 048 000, which puts branch dimensioning back on again because the branch has more than two components.