Use 3" x 8" or 3.5" x 8" cylinder?

[sixdogs]

I am rebuilding a 5,000 lb 12 ft wide cultimulcher ( a double packer with harrow in the middle) and wonder if I should use a 3x8 or 3.5x8 cylinder on it. The manuals I can find for this are pretty sketchy but they seem to use a 3x8 on a 12 foot and 3.5x8 on a 13 foot unit. Since I'm so close to the 13 ft size my "more is better" thinking says to go with the 3.5x8 size because the unit is so heavy and the 3.5" will be less stressed by the weight and bouncing around of the unit. During transport or driving on the road there is a bar I can use that holds the unit up without relying on the hydraulics.
Can anyone offer any advice on this? Thanks in advance.

 

[gzfrt9]

I have about the same unit. Brillion MD148 13 feer. I use 3.5 x 8

 

[RickB]

I'd be more concerned with the cylinder's rod diameter than the choice between 3" and 3.5" bore. Pick a cylinder with the largest rod and 3000 PSI rating.

 

[J_J]

Maybe something like this.

Surplus Center - 3X8X1.75 DA HYD CYL HEAVY DUTY CROSSTUBE

Surplus Center - 3 X 8 X 2 DA HYD CYL

Surplus Center - 3.5X8X2 DA HYD CYL HEAVY DUTY CROSSTUBE

 

[SSdoxie]

Difference in 3" to 3.5" cylinder piston is 26.5%. It will require 26.5% less pressure to lift the same load, but slow down the extend time at same pump flow 26.5%. If the extend/lift time is not an issue the larger cylinder will have less strain on the hydraulic system.

 

[sixdogs]

I have about the same unit. Brillion MD148 13 feet. I use 3.5 x 8

Actually we have the same size unit. A 12 ft Brillion is really the 148. Guess it's close enough for government work.

 

[sixdogs]

Thanks for the good advice. It makes sense that the rod diameter is an important factor. I used to lnow that but forgot--duh on my part.
Some hydraulic cylinders at the farm stores are rated at 2500 psi and I see some listed that are 3000 but are special order. Why is this and what difference does it make? Thanks again.

And some cylinders are ASAE. Why the difference?

 

[RickB]

2500 PSI used to cover just about all farm tractor hydraulic systems, now not so much. Moving the cylinder to full extension or retraction will build relief pressure in the cylinder. If your tractor exceeds 2500psi relief pressure, you are exceeding the design limits of a 2500psi cylinder. A big deal? maybe, maybe not. You be the judge. Farm supply stores generally sell on price, and a 2500 psi cylinder will usually be cheaper to buy than a 3000 or 3500 psi cylinder. Some buyers don't need the extra rating, some don't know that they need it, and some don't care whether they need it or not.