There is a "Catch 22" going on there. I'm not as familiar as Old Magnet is with all the stats, so just have to guess on this. Now THAT can get me in trouble quickly, but here goes.

If you increase the size of the cylinder to deal with low pressure but at the same time decrease the leverage advantage to get the movement you want, you've effectively negated any gain from your bigger cylinder.

The volume of fluid required may be actually be equal. You need so much movement with so much force and you choose between long thin cylinders with no linkage or short fat cylinders and long linkage. If you only have so much pressure you're sort of boxed in. Or you use massive cylinders to get the stroke and then need a HUGE pump flow to keep the speed of the action right. As time went on pressures have certainly gone up........no question about that.

It does seem that lower pressures are the culprit. You could always just have a bigger pump if flow was a problem. But you probably can't get past seal issues in the pump, more than likely. Higher pressures would require more precise (or expensive, even if possible) machining and design. Metallurgy may have also been an issue. Dirt and corresponding wear would be more critical.

There may have been cylinder seal problems too. Higher pressure would require better seals, and materials could have been a problem there too.

I seem to recall that some of the seals in my Cletrac cylinders are actually cast iron.....like a piston ring.....along with cups?? Mind is failing. But those are small cylinders. They're also newer, maybe the early fifties? Never mind. When were O rings developed?

That's what we need! A hydraulic history expert! Anyone out there?

Even with all that being possible, (remember, I'm just guessing on ALL of this), the linkages seem border line insane. Searching for a better mouse trap? Patent obstacles? Huh?

Then there's this: I worked with an engineer on developing some exercise machines, and he really enjoyed complicated solutions. I mean REALLY complicated. My favorite was his solution for a seat adjustment requiring more levers, pawls, springs, pivots, machining and overall crap than I could ever explain. Rube Goldberg would have been proud. It was an engineering marvel, but totally nuts. We discovered a counter-solution that was a lever, a spring, and some notches on a rod. Maybe they just had bad engineers. Ha!

MikeA

Hi MikeA,
Think your summary is pretty much on target:D
As far as history of hydraulics, I think it pretty much has its roots in War II.
The old "43" tin can I was on had assorted hydraulic systems, gear pumps, medium pressure hydraulic assisted steering (can't remember the pressure, think it was 1,200 to 1,500 psi.) Aircraft hydraulics was also coming on fast.

For some reason Cat got hooked on vane pumps....which limited pressures.
Believe I read some where there was concern for cold starting loads and the vane pumps offered near zero low speed starting pressures.

Considering some of the early Cat dozer applications and the fact that the #40 scraper was the only crawler pulled scraper to go hydraulic you could hardly say they were innovators in the field. Took a long time to overcome the "cable" mind set I guess.

One of the big reasons for maintaining the operating pressure in the 1000 to 1500 pound range was the state of the art in piston seal technology of the time. There is not a lot you can expect out of horse hide.

Yes, I would agree, seal materials were pretty limited.....but getting back to the original topic there doesn't seem to be much logic for some of the goofy linkage, like the D4 for instance. Didn't take long before that same limited hydraulics was doing the direct blade control on the D6-up in the same era.

Still seems like a Rube Goldberg application (D4) to get a hydraulic dozer mounted on something that was never intended. Didn't take Dakota and others long to figure it out.

You are right, the D-4 linkage is definitely designed by Rube and built by Goldburg. It would be interesting, over a nice cold beer, to hear a retelling of the original design thinking.

Early crawlers were not designed for dozer blades this resulted in the hydraulic rams being mounted outside the track frame and the need for linkages etc. Many large crawlers used cable controlled blades into the 1950s

My D47u came with a Bros dozer from CAT in 1953. It always seemed to me to look much more modern than the CAT built blades. It used longer and smaller hydraulic cylinders so it seems to be the opposite approach. There isn't any strange linkage and it all worked off the standard #44 hydraulic pump. It was my father's understanding that the dozer was built for the military and then released for civilian use as dozers were "rationed" during the Korean war. It's also quite easy to remove the dozer compared to the CAT ones. All you do is pull two pins at the hydralic cylinders and then undo the back half of each pivot point. I think the cable dozers with the wild framework are the strange animals.

I've not seen one like that before. It's definitely going towards a more modern approach, but then it's also a little newer than some of the craziest ones. The Kay Bruner on mine is probably older.......not sure what age but the tractor is a 1937.