Which side has more power?

[Donman]

Which side has more power?

While surfing an implement and miscellaneous auction Saturday, a friend and I noticed several hydraulic cylinder applications where the two way cylinders appear to be installed backwards. An example would be the main arm lift cylinders on a fel with the rod end on the bottom instead of the top. Common sense would say that the rod end of a two way cylinder has less square inches and therefore would produce less lifting power. Why would they be installed this way? Would they be faster acting because it takes less fluid to fill that end of a cylinder? Can anyone with hydraulic knowledge enlighten us?

 

[chim]

Re: Which side has more power?

One of us is "backwards" and it could well be me. I can do better with a pen and napkin when discussing some of this stuff.

If the ram is fastened to the bottom support, and it needs to extend to lift the bucket, the surface of the end of the rod is the entire ID of the cylinder.

For down pressure, the area is the ID of the cylinder, less the OD of the ram, making it less powerful?...............chim

 

[Tim_in_IA]

Re: Which side has more power?

regardless of which way it is installed it should have the same power, unless you change where it mounts. You are still pushing or pulling with the same force. I would think this had more to do with keeping stuff out of the cylinders such as rain etc so they are more commonly installed ram side out??

 

[hazmat]

Re: Which side has more power?

As others have said orientaion doesn't matter

Extension force = pressure*area of cylinder
Retraction force = pressure*(area of cylinder-area of ram)

 

[CTyler]

Re: Which side has more power?

I don't understand how you would have the same power when retracting. Isn't there less surface area to push against when retracting? You no longer have the full end area to push against. The higher the surface area the more push.

 

[RobS]

Re: Which side has more power?

True, there is less force when retracting as Hazmat has shown in his equation. The force in a given direction has nothing to do with mounting attitude though /forums/images/graemlins/smile.gif

 

[CTyler]

Re: Which side has more power?

Agreed, doesn't matter right side up/down.

I was questioning the statement about pushing or pulling.

After re-reading it though I understand he meant you have the same power for a given direction wether its mounted right side up or upside down.

 

[TonyV]

Re: Which side has more power?

If my old brain remembers the stuff I learned in a first semester college hydraulics course, then F=PA (force equals pressure times area) where force is in pounds. As long as the hydaulic pressure remains constant, then the more area that it works against the higher the force will be. Therefore (this is a word us college profs like to use /forums/images/graemlins/grin.gif) the force acting on the end of the cylinder with the rod must be less than the force acting on the end without the rod. I also recall my old hydraulics prof of making a particular point of this.
(I reserve the right to blame old age on the misinterpretation of these facts as prestented /forums/images/graemlins/grin.gif)

...Tony

 

[Donman]

Re: Which side has more power?

I just realized when reading your replies that the fel cylinder was a bad example because when the cylinder expands it is pushing on the full diameter of the piston whether or not it is upside down. We did see other applications where we thought that more power was needed on the retraction stroke and then the diameter of the rod takes away some of the needed area for maximun power.

 

[DaveNay]

Re: Which side has more power?

</font><font color="blue" class="small">( I just realized when reading your replies that the fel cylinder was a bad example because when the cylinder expands it is pushing on the full diameter of the piston whether or not it is upside down. We did see other applications where we thought that more power was needed on the retraction stroke and then the diameter of the rod takes away some of the needed area for maximun power. )</font>

In strictly theoretical terms, one of the mounting directions will have very slightly more lifting capacity due to the fact that either the rod and piston assembly or the cylinder (bore) assembly will weigh more than the other one. This would mean a lifting capacity difference of perhaps 5-10 lbs depending on the bore dimension and stroke length.

Dave