I'm working on a project that is going to require some pretty one off hydraulic cylinders, so I'm on a mission to get schooled in hydraulics. My main concern is sealing on the wall. The tubes will more than likely be aluminum (thick stuff), what should be done to ensure a proper seal? I don't want to have to tear these things apart any time soon.
My next issue is the end caps. What is the best form of sealing on them? I was thinking o ring, but I'm not for sure as I can't seem to find many good pictures. What about around the hole where the shaft comes out? What type of seal here?
I know these may seem like kind of noobie questions, but it's something I can tackle, I just need some help with these issues. Thanks in advance
Andrew

 

The piston usually uses several rubber seals with hard plastic backers, the surface finish is usually pretty polished. If this is not something that will need to hold weight off the ground for an extended period, I wouldn't worry a whole lot about bypass and leakdown, as long as you were able to get the power out of it you need.
The shaft seal is pretty much the same thing, and the shaft is usually chromed to give a smooth surface that repels contaminants. There is also usually an extra lip seal to brush dust and debris off.
The end cap seal depends on design. Most I have seen are a crush washer, usually aluminum or copper, that needs to be replaced whenever the tube is opened up.
If this was my project, I'd be looking for ways to make an off the shelf unit work. McMaster-Carr has a large selection of cylinders, and all the engineering work is done for you.

 

Well, the issue is that is a relatively long stroke, and a narrow bore. And where the cylinder will be mounted is in a weight critical area, and a steel cylinder of the right length, but larger bore would be considerably heavier than it's aluminum counterpart. I figured I could use an actual chromed shaft meant for cylinders. It will be under a pretty light constant pressure, with blips of very high pressures and quite a bit of cycling.

 

What do you have in mind? They have 1 11/16" bore cylinders in up to 12" stroke lengths, but they are only rated to 600psi, maximum pull is 1776lbs, max push is 1884lbs. I think a long aluminum tube would have to be pretty heavy to handle high pressures and keep a sealing surface.
Is this for an aircraft of some sorts?

 

it might get some air time
The cylinder needs to have a stroke of around 20 inches (more than likely less), and the smallest bore that it can do without fear of bending the rod. I'm thinking along the lines of a hardened or chromoly shaft for the final product, but a regular steel shaft would do for mock up/r and d

 

andrew what you need is a hydrolic ram from an airplane. thats what started the hydrolic craze. if you want ill find you the aritical i found along time ago about it. any questions you might have please ask. i spent over 4 years as a hydrolic mechanic for the navy and about 6 years before that installing them on cars.

there are bone yards in cali and arizona that you can buy these long skinny cylinders from. most of these are rated 3000psi as thats minimum mandated by the ffa.

but to answer your ??? o rings with teflon backing rings seal the pistons with teflon on both sides. as for the shaft it is sealed with a o ring and teflon backing on the top side with a felt scraper backed by brass to clean junk of the shaft as it moves back into the cylender. also some are double action and some are single.

 

What are they used for on planes? landing gear?

 

I think I might source it out to a coilover company. The body's of a coil over is pretty much what I need, without the ears for mounting.

 

How about a set of dirt bike forks? Just have to remove the damping rod and all those
parts you won't need but think about the cycling they go through and very rarely
have leaks just out of nowhere.

 

when you get into planes bigger then cessnas they are used on everything from flight contolls to landing gear. when i worked on p3s we had some that had 6inch throws to 18 i think so it just depends on what you get them from.

 

http://www.alliedbearingsandseals.co...t&grp_id=79122

This site should have all the seals you need.


Allso I learned a fun fact the other day about cylenders, That is even if you have no seals on the piston at all the cylender wont creap down, because of the space the rod takes up it makes some sort of pressure diffrence. Most people think when a cylender creaps down it needs new seals but usually its because of a leaking spool valve.

 

I actually have gotten FOA shocks to supply me with some flawed coilovers to do my testing on. Since these go through the same torture I'm building for, they should work great with some modifications. Now just to get it all in the works. My main issue is funding, since the next most expensive parts on my list have nothing to do with the automotive industry, and I don't think anyone will sponsor.