Pull-off force: hose, pipe, clamp

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Discussion Overview

The discussion revolves around the pull-off force in a hose-pipe-clamp assembly, particularly focusing on the effects of clamp torque on the connection's performance. Participants explore the mechanics of how torque influences the interaction between a rubber hose and a soft plastic pipe, as well as the implications of these interactions in practical applications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that a study showed negligible changes in pull-off force with a 10% reduction in clamp torque, questioning if higher torque might deform the pipe and reduce friction between the hose and pipe.
  • Another participant asks for clarification on how this thread differs from a previous discussion, emphasizing the need for a diagram to aid understanding.
  • Participants discuss the differences in focus between this study and previous ones, highlighting the absence of grooves in the current assembly and the material differences (plastic pipe vs. steel pipe).
  • One participant expresses frustration at being questioned about their use of forums for proprietary work, asserting their engagement is driven by personal interest rather than necessity.
  • A participant describes the mechanics of hose behavior under tension, explaining how pulling on a hose can lead to a reduction in diameter and a constant surface area, which contributes to a positive feedback mechanism in the connection.
  • Another participant asserts that minimal initial clamping is sufficient to initiate the positive feedback effect, suggesting that additional clamping beyond a certain point may not be necessary.

Areas of Agreement / Disagreement

Participants express differing views on the effects of clamp torque on the pipe's deformation and the necessity of additional clamping. There is no consensus on the implications of these factors for pull-off force.

Contextual Notes

Participants reference previous discussions and studies, indicating a complex background that may influence their current views. The absence of a diagram is noted as a potential limitation in understanding the mechanical interactions being discussed.

jbenedet
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Was surprised by a study recently where we tested 6 samples for pull-off force at a 10% reduction in clamp Torque and noticed negligible shift in results. Is it possible that at higher torque the clamp is deforming the pipe, reducing the surface contact (friction) between the hose and pipe?

The pipe is a soft plastic, the hose is rubber, the clamp is steel. The pipe is inserted into the hose and a clamp is torqued down over the connection.
 
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It’s similar but different. This is a study focused on the torque of the clamp. The other was for clamp position. This assembly also has no groove unlike the other example and is a plastic pipe, instead of a steel pipe. I am being careful not to provide proprietary information while still including enough info to work through the concept. Also, the community provided good ideas/brainstorming based on the info I provided previously. It was helpful. Thanks.
 
jbenedet said:
It’s similar but different. This is a study focused on the torque of the clamp. The other was for clamp position. This assembly also has no groove unlike the other example and is a plastic pipe, instead of a steel pipe. I am being careful not to provide proprietary information while still including enough info to work through the concept. Also, the community provided good ideas/brainstorming based on the info I provided previously. It was helpful. Thanks.
Do your managers know that you are having to resort to Internet forums to do your proprietary work? Are you working as an ME?
 
berkeman said:
Do your managers know that you are having to resort to Internet forums to do your proprietary work? Are you working as an ME?
This is so incredibly out of line it’s ridiculous. I’m not “resorting” to anything. I’m thinking about this because I enjoy it, not because I can’t get my work done.
 
It is often the case that you can more easily push a hose on, or off a pipe, but you cannot pull it off. When you pull on a hose, the tension causes the hose becomes slightly longer, while the diameter of the hose is reduced. The surface area of the hose effectively remains constant. That is the source of the positive feedback.

The hose must be clamped sufficiently to the pipe, that the internal fluid under pressure, does not penetrate between the pipe and the hose, under the band of the clamp.

jbenedet said:
Is it possible that at higher torque the clamp is deforming the pipe, reducing the surface contact (friction) between the hose and pipe?
No.
Very little initial clamping is necessary to start the positive feedback multiplication. Once the clamp is snug, additional clamping will be unnecessary.
 
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