Valve Opening Query

I disagree. You have no understanding of the concepts of pressure and torque. If you did then you would be able to recognize the forces required to make a valve operate.

It's a 12" valve with a 485 bolt circle.

Has nothing to do with opening force.

redfred is right. You get zero points for that question.

Better hit the books some more.

It depends on what type of valve it is, and also on manufacturing specifics. It cannot be precisely calculated from first principles alone.

This is best viewed in the idealized case, because then no math needs to be done. Ignore the gear operator ratio. Assume fluid pressure to be zero. Ignore area against which pressure will create force. Assume no o-ring or other sealing device contact pressures. Assume zero friction in all moving parts. Ignore mass of valve parts.

In that case, the valve opening and closing torque will be 0 lb-ft.

Is that an exact figure or will it be 'more or less'? -- JHF (just stirring the stuff!)

As per API code opening Torque requirement should not exceed 35kg-m (350Nm) irrespective of size and rating . . . if it exceed go for gear operater . . .

Thanks