self contained, passive top link

[Brad_Blazer]

If the top link load is tension only which seems reasonable for your application the single valve should work. I was thinking more of a general purpose top link which sees loads in both directions.

115psi is the absolute pressure of the 100PSI preload. Actually, working against a void only counts for the (cylinder - rod) area. The preload pressure against the rod area is gauge pressure since the far end of the rod is exposed to atmosphere.

If there is no preload the only resistance to compression is Patm * (Acyl - Arod). That's about 50lb for a 2.5" cylinder.

One more consideration. Even if you don't normally require compressive force, if the cylinder is locked near full extension as you have it valved and it inadvertently gets compressed, all of the oil will be pumped into the reservoir.

 

[PILOON]

It would cost a mere few $$ of plumbing to experiment as follows:

Fill the cylinder and lines with a needle valve plumbed in the line.
The needle valve will control the speed of 'let down' or dump.
Sure there is a differance in volume between sides of the piston due to the shaft but I doubt if it matters enough to even notice.
Also the lines could be long enough to position the valve handy to the driver's location.
As a load increases there might be some sag as the fluid compresses but that should be minimal.
Operation would then be; (with valve open) manually lift the rig, close valve to hold position and open valve as required to control the dump action!

I know it can work as I once rigged a plow using a single action cylinder hand pump and needle valve.
Also a hand pump and single action cylinder would work (or modify the double action to single action.)

 

[Brad_Blazer]

If you just want to use 1 valve, plumbing for single action with a reservoir is probably the way to go.

 

[ford860]

Okay, so now I'm intrigued again. I've included an image of what I had envisioned for the self-contained hydraulic top link. I trust the experts (and there seem to be few) to critique the design and offer improvements.

I know this or a similar design will work, but need your help.

Many thanks in advance.



Ford860

 

[ford860]

Oh yeah,

Please feel free to make fun of the illustration. I like AKKKAMAAN's better.

 

[Brad_Blazer]

That's a fine illustration - What is that, an old Case?

I would get rid of the tee and put a vent filter on the left end of the cylinder in your drawing. Oil in the left end doesn't do much besides make the system more complicated. The reservoir needs to be vented too.

 

[ford860]

Brad,

I understand both of your recommendations; yes, it's a simpler system. But, will the cylinder wall be subject to scaring if the "left" side does not have more than a thin film of oil in it?

Thanks,

Ford860

 

[Brad_Blazer]

Check out the breather vents at the bottom of this page and the stated function. I don't have personal experience but I think a thin film should be enough as long as rain can't get in the breather.
http://www.baumhydraulics.com/files/catalog/h26.pdf

 

[ford860]

Thanks Brad,

I actually ordered one just like it yesterday from Burden Surplus Supply.