Snubber selection

ROHR2 Dynamic calculations, questions and discussions
ROHR2stoss - Structural Analysis with Dynamic Loads using Direct Integration
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r2user
Beiträge: 135
Registriert: Mi 14. Sep 2011, 10:18

Snubber selection

Beitrag von r2user » Mo 26. Sep 2011, 14:55

Hi

Could you explain how to chose a snubber for fluid hammer forces.

Best regards

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rohr2support
Beiträge: 393
Registriert: Mi 14. Sep 2011, 08:23

Re: Snubber selection

Beitrag von rohr2support » Mo 26. Sep 2011, 15:01

The snuber selection is a multi step process:

1. At first a calculation without shock absorbers is carried out. You should check that the displacement at the location where you plan to use the snubber is at least 5 mm. Otherwise the snubber will not have a big effect.

2. The support load (from dynamic load) on a rigid support that is inserted at the place of a shock absorber is calculated.

3. A shock absorber is selected, defined for max. support load calculated in 2.

4. The stiffness of the shock absorber is estimated, e.g. as defined by LISEGA: c=FN/S with FN as max. load and S = travel range of the shock absorber under max. load (ca 3-6mm)

5. Insert this stiffness into the snubber in the pipe stress model and check loads and movements. At the shock absorber a travel in the size of S (see 4.) should appear.

Generally:
- shock absorbers near anchor points are useless – forces will find their way directly through the pipe to the anchor point and the movement at the pipe is too small to have an effect on the shock absorber.
- Parallel shock absorbers do not work. The load will not be distributed on several shock absorbers: the first shock absorber will block and hinder the blocking of the next ones.
This is also valid for several shock absorbers in axial direction along a long straight line. Exception: pairs of shock absorbers at special heavy duty clamps working in that way, that the blocking of a Shock absorbers increases the movement of the 2nd shock absorber.
-The support stiffness (steelwork behind shock absorber) must be more rigid than the shock absorber in blocked state (calculated as shown in step 4 above)
-when the travel range is below the clearance of the shock absorber (ca 0.5mm) the shock absorber will never work
-shock absorbers can not absorbe static loads.

There is a small animation showing the optimization of a system with additional rigid supports and a snubber.
http://training.rohr2.com/html/damper.html

Best regards

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