fuzzy math on log splitter ratings

[sizzami]

I keep reading ads for log splitters with 4" cylinders 3000 lb two stage pumps w/ ratings up to 27 ton according to my calculations the max you get with that set up is 18.85 ton any body know how they come up with these big numbers?

 

[Eric_Phillips]

This is just a guess. Did you take the pressure assuming 4" area? I bet they measure at the edge of the wedge which might have less than 4" surface area.

 

[J_J]

I keep reading ads for log splitters with 4" cylinders 3000 lb two stage pumps w/ ratings up to 27 ton according to my calculations the max you get with that set up is 18.85 ton any body know how they come up with these big numbers?

All 4 in cyl at a pressure of 3000 psi will have the same rating. At 2300 psi, force will be less.

extend force will be 37,699 = 18.84 tons
retract force -------28,274 = 14.13 tons

The two stage rating is for 3 GPM, at 2500 psi, 11 GPM at 650 psi so the relief valve is probably set around 2300 psi.

They also cheat the same way with pressure washers. You only see 3000 psi when you release the handle and it goes into relief. The smaller orifice you use, the pressure increases.

Same thing with peak watts, and avg watts.

The push cycle timing will change depending on the wood being cut. If it goes into slow mode/high pressure, the cycle will time will increase. Return stroke is usually in the low pressure high GPM mode.

 

[AKKAMAAN]

This is a very common problem in the log splitter biz.....there is only a few manufacturers that post ratings that match with the math...

They fault on both splitting force and cycletime....

They dont post system pressure, and post like a 25 ton rating that will require a 4000psi system pressure....Almost all logsplitter components are rated for 3000psi at the most, usually less.....
They also post pump capacity in GPM with out telling at what rpm...that right way to to describe pump capacity is to tell the displacement per rev and the max speed or RPM....

Speeco is one of the worst to mislead....but they also have one the the best customer services out there.....

this has been discussed a lot on arboristsite forum
http://www.arboristsite.com/forumdisplay.php?f=55


BTW, what do you prefere....2-stage pump or 2-stage cylinder?

 

[J_J]

This is a typical example of the specs on a 16 GPM hyd pump. With this data, you can figure the speed, and tonnage. Engines usually run at around 3600 rpm.

2 STAGE HYDRAULIC PUMP
Brand new 2 Stage log splitter pump for faster cycle and larger cylinders. Quality built, needle bearing equipped, case hardened gears. High performance uploading valve, reverse flow check.
Use with 8 HP engine.

SPECIFICATIONS
.776 cu/in displacement low side
0.258 cu/in displacement high side
3000 PSI max
4000 RPM max
First stage 16 GPM @ 650 PSI
Second stage 4 GPM @ 2500 PSI
16 GPM @ 3600 RPM

 

[Reg]

I could do some fun "brochure math".
From cylinder diameter and hydraulic pressure derive the force available at the end of the cylinder.
Divide that by the (small) area of the long thin wedge to get "splitting pressure", a very HIGH number, but not meaningful.

 

[AKKAMAAN]

I could do some fun "brochure math".
From cylinder diameter and hydraulic pressure derive the force available at the end of the cylinder.
Divide that by the (small) area of the long thin wedge to get "splitting pressure", a very HIGH number, but not meaningful.

Actually I think you are pointing out a very important thing about "split-ability"....a long thin wedge, and not so wide, will split easier than than a short, wide, non sharp one.....I think it is very meaningful to concider........
Way more can be done on wedge design.....like reducing initial friction.....


J_J......those specs you are showing is exactly what should be provided, but it is not.....displacement per rev is VERY rare....aswell as all the data on the 2-stage pump.....

 

[Reg]

Actually I think you are pointing out a very important thing about "split-ability"....a long thin wedge, and not so wide, will split easier than than a short, wide, non sharp one.....I think it is very meaningful to concider........
Way more can be done on wedge design.....like reducing initial friction.....


J_J......those specs you are showing is exactly what should be provided, but it is not.....displacement per rev is VERY rare....aswell as all the data on the 2-stage pump.....

Well; "Yes", "No" and "I was joking".
Certainly the wedge can be "sharp" to start the split, but within an inch, more/less, it is good if it flares out and OPENS the log.

Cycle time is meaningless on a lot of wood.
It is possible to grab the wood as soon as it "pops", maybe 4 or 5 inches of stroke, and tear it apart as you toss it to the pile.
I attribute this to the fact that my wedge is WIDE 4 inches back from the edge.
A "blade" would catch on the sides of the opened log as it went through and "plane" big slivers off - not something I would want, but I don't wear gloves (-: