Gland tightening torque

[Daren Samy]

Vendor has not provided torque for gland tightening of 10' control valve. Is there can be any rough idea for torque gland tightening? Many 10' valve gland tightening torques that I know vary from 20Nm to 30Nm depending on bolt size.

Daren!

 

[gerhardl]

The only people with the correct answer is the constructor/factory. But yes, 20-30Nm is a quite normal range.

 

[PeterIgg]

My stock reply to: How much torque to apply to gland packing?" is:
"Until it stops leaking!"
Not a particularly useful response, I'll grant, but the best one I can come up with.
There are SOOOOO many variables with gland packing, not least: the size and number of the gland bolts, the type of packing, the number of rings and the area of the packing. The OEM really has to come to the party with some recommendations, they built and tested (presumably) the valve in the first place, but if you are in the field the state of the threads on the gland bolts will be a major factor and I revert to my original statement. However, without wanting to teach my grandmother to suck eggs, if you over tighten all you will do is make the valve difficult to operate and exacerbate the wearing of the packing.

 

[TugboatEng]

From an operator's perspective tighten until it stops leaking means a valve that can't be closed by hand.

 

[Danlap]

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