First of all, a manufacturer which cannot provide torque values of their own control valve, then there is something wrong with them. Assuming this is a question from end user (representative) since most suppliers do not want to disclose their valve details to competitors.
What was the reason you want to perform re-tightening? Was it start showing hysteresis hence alarm went on, or is it leaking? If leaking, then the approach usually 2x quarter turn – (partial) stroke valve and repeat until leakage is stopped.
Not to simplify, I’ve did some calculation in the past for manual valves (gland: 1xcord – 3x pre-compressed graphite – 1xcord) using new B7 bolts. Without lubrication/molycote, then values as below. Torque values on the right maximum side is before it reaches maximum sealing stress.
Bolt size Maximal gland torque
3/8” 10 to 25 Nm
1/2” 20 to 40 Nm
9/16” 30 to 50 Nm
5/8” 50 to 70 Nm
3/4" 90 to 130 Nm
7/8” 130 to 200 Nm
1” 160 to 240 Nm
1-1/8” 220 to 325 Nm
For control valve, with PTFE ring, lantern ring and installed one by one with pre-tightening then it will be different values. Usually slightly lower.
However, regardless values provided by manufacturer or independently calculated, once ones see that gland is already relaxed ‘a lot’, corroded bolts, skewed gland retainer, etc., then the tightening approach would be different and mostly depending on workmanship.
Regards,
Danlap
