Long-Stroke Hydraulic Cylinder Mid-Length Support Question

[tkanzlerpe]

I've got an unusual design issue where I need to use a spherical eye to spherical eye single-stage hydraulic cylinder operating primarily under compressive loads. I cannot mount it with trunnions or spherical cap at the gland, but I can support it against buckling (vertical installation, rod-down) if needed. Stroke is 15 ft.

The cylinder manufacturer says that there is a 4:1+ FoS on buckling, but I'm not so confident that it's really that high. For the sake of redundancy, is it possible, or for that matter advisable, to add lateral support (can make that very stiff) by putting either a loose collar around the gland end of the tube (1/2" clearance all around 14" OD), or for that matter, a tight one, though flexure in the installation may make it advisable to let the cylinder 'float' inside the collar.

This isn't just a straight Euler buckling problem, as the tube has a moment of inertia around 3.5 times that of the rod, and the tube isn't under compression in the normal sense.

Anyone have any thoughts?

 

[Jboggs]

I always use an internal stop collar in situations like that. It just basically reduces the effective stroke and stiffens the cylinder in the full extended position. You would probably use a cylinder built for a 17' or 18' stroke with an internal stop collar that limits it to 15'. Can you do that?

 

[tkanzlerpe]

That's already part of the design, but I'm still concerned about the extended length. I just downloaded the NFPA T3.6.37 R1-2010 (Method for Determining the Buckling Load), so I'll experiment with that. The standard does take into account the stop tube length, by the way.