Hose subjected to external pressure? 2

[btrueblood]

Has anyone had experience with hoses operating (at least some of the time) with an external pressure higher than the internal pressure? I have a device that will be operating submerged at up to 100 psi, and I need to plumb fairly low pressure fluid into it (typically 25 - 30 psi above the case pressure) via a flexible connection.

 

[kcj]

Pressure outward is easy to handle with high strength wires in tension. Pressure inward, compression, is very difficult. A 3000 psi hose may only resist 5 or 8 psi suction before collapsing inward.

Suction hoses have large wire helicals to support against collapse, but I have never heard of anything over -30 in hg (one atmosphere).

How about the undersea and oil rig industries, they must have conductors in these types of conditions.

 

[amorrison]

Thin wall to ID hoses will collapse under external pressure regardless of the material used (this is probably similar a long thin column collapsing - think structural engineering).

Consider a hose with very thick wall to ID ratio.

An example here - second picture

http://www.hyvac.com/Products/Parts/vac_hose.htm

 

[btrueblood]

Thanks to both of you. In general, it looks like a hose flexible enough for my purposes will have to be operated in a way to prevent a high negative pressure from collapsing it. A sister corporation to mine designs parts for subsea use, but they typically use oil-filled hoses/cables to prevent a collapse condition from occurring.

Will run off now and do some experiments with varying hose wall thicknesses and reinforcements. Since the condition is probably going to be a very rare occurrence, especially if cautions to operators are given to prevent it, I'm thinking of doing only a very nominal 100 to 1000 cycles of maximum expected negative pressure, and see how the hose holds up.

 

[zeusfaber]

Don't suppose there's any easy/affordable way you could increase the pressure within the hose and reduce it before use at the other end?

Or is there anything to stop you running the casing dry but pressurised to ambient? (Accepted that there are often lots of good reasons to not want to do this).

A.

 

[turbomachinary]

try bellow fittes hose