Hi
Could you explain how to chose a snubber for fluid hammer forces.
Best regards
Snubber selection
- rohr2support
- Beiträge: 455
- Registriert: Mi 14. Sep 2011, 08:23
Re: Snubber selection
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
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
- rohr2support
- Beiträge: 455
- Registriert: Mi 14. Sep 2011, 08:23
Re: Snubber selection
Hi
You are right: The old link is dead. The videos have been reworked from the old flash format and can now be found here:
https://www.rohr2.com/en/rohr2-trainingexamples.html
and this video about fluid hammer and snubber selection can be found here directly on Youtube:
https://www.youtube.com/damper
Thanks for the hint.
Best regards
Rohr2 Support
You are right: The old link is dead. The videos have been reworked from the old flash format and can now be found here:
https://www.rohr2.com/en/rohr2-trainingexamples.html
and this video about fluid hammer and snubber selection can be found here directly on Youtube:
https://www.youtube.com/damper
Thanks for the hint.
Best regards
Rohr2 Support