Our manufacturer is offering 850 mm wrench length due to high torque to operate the valve & we are afraid that such a long wrench will interfere when installed in the line. We checked the design STD API 609 but it is not clear as to what should be the max allowable torque. Our manufacturer is offering hand wheel operation but my end user requires wrench operation only. Please advise how to determine the max allowable torque for this valve (butterfly valve 6”, CL 150, BS 1400 ALLOY AB2, SHORT WAFER, FLANGELESS, WRENCH OPERATED)