Hard stop or cylinder stop

[6sunset6]

What is the opinion on what should happen at the end of a cylinder stroke. Should the motion come to a hard stop mechanically before the cylinder bottoms out or should the cylinder bottom out first. I guess the question is which prolongs the life of the cylinder?

 

[J_J]

The piston is going to hit something.

Even if you put a stroke limiter inside the cyl, it will still hit the stroke limiter and stop, the same as if the piston bottomed out. Same pressure.

 

[oldnslo]

The style or method of stopping a cylinder and or load depends on several variables in no particular order:
Cylinder velocity
Load on cylinder
How is cylinder mounted: rod up, rod down, horizontal, etc.
Cylinder type and mounting method.

example(s):
A 4" bore cylinder mounted rod up with 1000 lb load traveling at 1 inch per second probably does not care how it is stopped since inertia is not that great for that size of a cylinder.

a 1" bore cylinder mounted rod down with 1000 lb load extending at 30 inches per second would probably destroy the cylinder in short order if allowed extend fully till it hard stopped at that velocity.

I realize these two examples are at the extreme ends of design but I am hoping this illustrates some of the decisions that should go into deciding how to mount and or stop a cylinder.

I have seen a few cylinders with ends pulled off the rods when extremely heavy loads creating high cylinder velocities hit end of stroke.

 

[6sunset6]

That's helpful This is a crusher jaw (see crushing concrete in projects) two possibilities a 3.5 diam or 5 diam on 7gpm stroke is 10 inches so it might range from 3.5 sec to 5.8 sec . Both are relatively slow so I think it will not matter much.

 

[glastron23]

How is cylinder mounted: rod up, rod down, horizontal, etc.
Now there's an interesting question??? what is the best way to mount a cylinder???? Rod up or rod down??? and WHY??? should be a good read!!!! LOL

 

[6sunset6]

It's rod down. It fits better that way. Although rod up would keep the shaft away from crushing material. I was going to cover it with some sort of sliding cover , like a stove pipe .

 

[CalG]

If the mechanism is at a position of compromised mechanical advantage, stop the cylinder.

If the mechanism is in a robust position, use the mechanism.

You won't hurt the hydraulic cylinder by running it to the end of stroke in either direction. (Unless the cylinder has some sort of deficient design.)

The connecting linkage is everything. I have seen linkage arrangements that deflect the hydraulic cylinder in bending at the end of stroke. THAT is example that is best met with a cylinder stop!

 

[banjodunn]

G'day cylinder should always stop before machine stroke stops it, I have seen way too many cyl rods bent because the operation of the machine stopped and the cyl was still trying to push.


Jon

 

[6sunset6]

Now that makes sense. Thanks

 

[oldnslo]

How is cylinder mounted: rod up, rod down, horizontal, etc.
Now there's an interesting question??? what is the best way to mount a cylinder???? Rod up or rod down??? and WHY??? should be a good read!!!! LOL

In a dirty environment some people believe that rod down is the best approach. This allows the dirt to be scraped or wiped off the rod easier when the cylinder is being retracted. I.e. dirt does not build up as easy on the end cap.

Properly designed, mounted, and supported a cylinders extend force should never bend the cylinder rod. What usually bends the rod is an external force. An example of this is the curl cylinders on an FEL. I don't believe I have ever read of a rod being bent while trying to dump the bucket and lift the front of the tractor off the ground. Now add the extra force of the tractor backing up and the bucket lip hitting something solid and you can easily bend the rod.