Pressure Thrust into a larger chamber..

[simmantix]

Hi,

If I have a pipe connecting to a 750mm diameter vacuum chamber via an unrestrained 500 mm diameter bellows, can someone confirm that the thrust pressure that would work to collapse the bellows under vacuum would be based on the diameter of the bellows and not the chamber?

I am pretty sure that it is but this keeps nagging at me. The pressure, as I work it out, should lift about 2 tonne.

Thanks..

Simmantix
---------
Phases of a Project:
Exultation, Disenchantment, Search for the Guilty, Punishment of the Innocent, Praise for the Uninvolved...

 

[simmantix]

Sorry, meant thrust pressure..

Simmantix
---------
Phases of a Project:
Exultation, Disenchantment, Search for the Guilty, Punishment of the Innocent, Praise for the Uninvolved...

 

[BigInch]

Internal pressure causes axial tension and hoop stress tension in the bellows. That won't collapse anything. Thermal loads from increasing temperatures of attached piping is what usually causes axial compression in a bellows.

Independent events are seldomly independent.

 

[LittleInch]

Can you sketch this and post it as I can't quite work out what your system is.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[simmantix]

Just to re-iterate, its a vacuum system with a bellows joining the pipe to the chamber. I want to design the tie-rods or perhaps put in a pressure balancing joint so.. My question is: what is the force acting to collapse the bellows due to the vacuum within the system?

Awful drawing attached..

Simmantix
---------
Phases of a Project:
Exultation, Disenchantment, Search for the Guilty, Punishment of the Innocent, Praise for the Uninvolved...

 

[MikeHalloran]

The pipe and the chamber should be supported, by something other than the bellows.

The bellows does not need tie rods or other funny business, >>>>once installed<<<<, because a bellows under external pressure is stable.

The bellows may be shipped with some sort of tie rods or straps to limit the amount of damage that can be done to it during shipping and handling. Any such restraints should not be removed until the bellows is secured in place between the pipe and the chamber.

If you anticipate pressurizing the inside of the bellows at any time, e.g. for cleaning, or some conjectural process, or just by filling everything with water, or whatever, you should consult with the bellows manufacturer about what sort of restraints, if any, will be required to deal with that nonoperating internal pressurization.




Mike Halloran
Pembroke Pines, FL, USA

 

[simmantix]

Sorry, are you saying a bellows installed at free length will not axially compress under vacuum?

Simmantix
---------
Phases of a Project:
Exultation, Disenchantment, Search for the Guilty, Punishment of the Innocent, Praise for the Uninvolved...

 

[MikeHalloran]

A bellows installed with one end fixed and one end free to translate will indeed shrink axially.

It should not be installed that way; both ends should be fixed to the greatest extent possible. The bellows is there to compensate for the extent to which its ends cannot remain absolutely fixed.

You can use a bellows in a way where one end translates, for example as an aneroid. Its life will be severely limited in that situation.



Mike Halloran
Pembroke Pines, FL, USA