6 inch gate valve position

[529]

Recently I took a exam asking how many turns does it take to close a 6 inch gate valve for the full open position? I dont know the answer, so I guessed 19 turns of the whell operator since I had no references to go by. Does any one know the answer? Does anyone care? Just curious. BTW the question was civil service exam.

 

[bimr]

Good guess.

How many turns does it take to open/close a gate valve?

The AWWA operating formula for opening/closing a gate valve is 3 times the nominal valve size plus 2 or 3 turns of the operating nut.

Example; 6 x 3 = 18 plus 2 or 3 = 20 to 21.

 

[eddieng27]

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.

 

[MrWizard]

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.

Quite commonly, the valve manufacturer will have this final figure stamped on the nameplate also.

 

[RWF7437]

The reason anyone cares about this is simple. Imagine you are a water system operator and it is 3:00 am. A leak has developed and your job is to isolate the leak by turning off one or more gate valves. Suppose your valve is 6-inch and you have tried to close it. After 25 turns the leak still has not stopped. You now know that the valve stem is broken even though you can't see or feel it. You also know that you will have to turn off other valves in the system to stop the flow.

good luck