Being asked how many turns it takes to close a 6 inch gate valve for the full open position.
The previously given advice of 3 times the nominal diameter plus 2 = number of turns to open/close a gate valve is generally pretty good.
It should be remembered this will not hold true on large valves that have a gearbox installed (either spur gears or bevel gears.) The gearbox should have a nameplate attached giving the gear ratio. This needs to be factored in.
For example, for a 60" valve, the number of shaft turns should be 3 X 60 + 2 = 182 turns. If the gearbox has a 3 to 1 ratio, then the turns figure must be multipled by 3. So, with a 3:1 gearbox, a 60" valve will take 546 turns of the input shaft to fully open/close the gate valve.Manufacturer's data will often list the number of turns to open the valve along with the required torque.  You might have to dig a bit, but it will be there.  bimr has the formula that should apply also, particularly for AWWA rated valves; but most valves have that rating now days.

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