Calculating Tightening Torque for Bolt Packing

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    Bolt Torque
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Discussion Overview

The discussion revolves around calculating the tightening torque for bolts used in valve packing applications. Participants explore methods for determining the appropriate torque while considering the effects of packing compression and gland deflection.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests using a torque wrench or measuring bolt elongation as methods for determining tightening torque.
  • Another participant emphasizes the need for the packing to compress adequately to seal without restricting the stem's movement, noting that excessive force can lead to premature packing failure.
  • A later reply questions whether the original poster (OP) is seeking to understand how to measure when the desired torque is reached, rather than how to calculate it.
  • The OP specifies the use of metric threads, particularly M6, in their application.
  • The OP describes the mechanics of the gland arrangement and seeks methods to calculate both the necessary tightening torque and the resulting deflection of the gland arrangement.

Areas of Agreement / Disagreement

Participants express differing interpretations of the OP's question, with some focusing on torque measurement methods while others address the implications of packing compression and gland mechanics. No consensus is reached on the best approach to calculating the required torque or deflection.

Contextual Notes

Participants mention various factors influencing torque calculations, such as the type of packing material and the smoothness of the stem finish, but do not provide specific mathematical formulas or assumptions underlying their claims.

gopinathaengg
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hi, thank u
we r using packing's in our valve.packing's are tightened by bolt.how to calculate tightening torque,while tightening bolt.
 
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Can you elaborate a little? What kind of screws are you using?
 
You do it the same way you would in any other scenario. You either properly lube the bolt and use a torque wrench or measure the elongation of the bolt as it is being torqued (most accurate method).
 
If you are talking about the nut that tightens the packing around the stem of the valve, that is another story. The packing must "crush" enough to make a seal at the stem, but can not be tight enough to stop the stem from moving. Too much force, especially with soft packing (teflon) may cause pre-mature packing failure. The stem that rides on the packing needs to be smooth. the finish is directly resopnsible for packing life and ability to seal at pressure.
If you only calculate the max force needed for the thread size and use this as your baseline, the force may be excessive vs what the product needs.

dr
 
That is true, but I don't think that is what the OP was asking. To me it seemed like they already know the torque they need, they just want to know how they can know when that torque has been reached while tightening.
 
metric threads used for tightening bolt. for example M6
 
packing is pushed by gland arrangement with help of bolt.so while tightening the bolt the gland will deflected.it will occur the gland arrangement is couch the stem. so gland is jam with stem.now i want to calculate the how much tightening torque and also how much deflection will occur in the gland arrangement. any calculation method is available.
 

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