Comparing stuff is always interesting, so when two weeks ago I wrote my post about the "longevity monster" - Parker's PV plus series PV140, I thought that it would be great to compare its internals to its "similarly sized" European brother - the Rexroth A10VO140.
Of course, the A10VO is medium-duty, and is a lot cheaper, so the comparison could never be direct. It would rather serve as a means to show how seriously heavy-duty design can differ from medium, but, unfortunately, I didn't have an A10VO140 in the shop on that day... Right until the very next day, when one of them popped up, as if by magic! I am using this opportunity to showcase the parts side by side, and also (after doing some simple math) uncover another "longevity ace" that the PV140 has been secretly holding up her sleeve all this time.
Let us start with the swash-plates and their bearings. You don't need to know anything about pumps or mechanics to be able to tell which one is heavy-duty:
I mentioned in the previous article how I liked the segment-based slipper retaining system of the PV, and these pictures show why - look at the typical wear of pin/ball guide system, these needles bite pretty hard, don't they?:
Here's the end plates, the shafts and the valve plates, and the servo pistons:
Maybe end-plate-wise, and even valve-plate-wise this could be a tie (even considering the ripple chamber of the PV and all) but the shaft and the servos leave no doubts about who is "strongest" here. But the biggest "surprise", so to speak, comes from the rotary groups:
Hold on for just a minute, something doesn't add up here! Why the hell are these pistons so large? It's 28 mm in diameter vs 25. That's a lot. If you calculate the areas - it's 4.9 cm² vs 6.2 cm²! And the PV barrel looks bigger as well. Just have a look at how the PV Piston towers of the A10VO's.
The things become clear if you do as you always should when you have doubts about a pump - check the tech catalog and the respective parts list.
The catalog will tell you that the PV series has several frame sizes and that frame 4 comes in two displacements - 140 and 180 cm³, and then if you check out the parts list - you will see that both displacements use the same parts for the rotary group and that the only part that is different is the small displacement limiter, so the 140 is actually a limited 180. Now let us go just a tiny bit further and add some math to the mix:
Since I have the barrels with me, I measured the "b" for both of them, and it is precisely 100 mm for the Rexroth A10VO140 and 104 mm for the PV140. Now, if you do the math for the 25 mm and the 28 mm pistons and the 140 cm³ displacement, you will see that the max swash-plate angle for the A10 is 17.6º, and for the PV140 is only 13.7º. If you consider the displacement of 180, you'll get the angle of 17.4º for the Parker, but the whole point (and the aforementioned "ace up the sleeve") is:
The PV140 runs with the lower swash-plate angle of 13.7 degrees, which means that the relative speeds and, consequently, the wear inside the (already over-sized) piston ball/slipper assembly are lower. This, in my opinion, is another factor that adds a great deal to the "robustness" of this pump!
See - a tiny bit of math can be fun! Wait... Did we just discover a hydraulic pump "longevity hack"? Is there something in running bigger pumps at reduced displacement?
I don't know about all the pumps, but when the manufacturer uses this trick - i.e. providing two or more standard displacements in the same frame size with the only difference being the mechanical swash-plate stroke limitation - I believe the "throttled down" versions have all the chances to last longer.