Jeffersonville, OH | Tazzerblue - 1/9/2026 17:08
that might explain the extreme pressure for that era. Anyone know why the industry settled on 2000-2250? and now around 3000?
Well, the Allis is a fixed displacement piston pump, 3-4 pistons running off a camshaft in the center housing of the tractor if memory serves correctly.
Everyone else seemed to settle on Gear, or some vane, pumps around the same time or after, and a typical gear pump is only good to around 2000-2500PSI...hence the lower ratings.
Deere Open Center systems used a radial piston pump for whatever reason they chose that, and I'm sure it can handle higher pressure than a gear pump, but I honestly don't care enough about those Deere models to remember what pressure they are set...sorry LOL
Around 1970 White/Oliver/Minneapolis-Moline started to go to an axial piston pump on their larger tractors, though I believe it was just pressure compensating, and not flow....I don't remember exactly when this change from gear pumps to axial piston pumps happened, because I think it was different depending on model.
1973 Allis went to the first pressure and flow compensating systems on the 7030/7050 tractors, and the rest of the industry followed eventually...some much later than others.
Smaller tractors still use gear pump, and Open Center systems because they are much cheaper, simple, and reliable...but the high flow, large demand or VARIABLE demand stuff all uses a Variable Displacement Axial piston pump as far as I know.
There's your history lesson from a guy who wasn't there but has been around...I'm not getting into a pissing match if my dates are off a bit and your favorite brand did it first, this is what I remember off my head!
EDIT: In case you don't want to read all that, Gear and Vane pumps typicallycan't handle pressure higher than 2500psi, Piston type pumps can!!!
Chris
Edited by c_mayer 1/9/2026 16:26
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wd 45 Allis Chalmers hydraulic pressure question/ HOW much PSI did they put out?
