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   The following is an add-on (10th May, 2010) for the article on John Deere Radial Piston Pump.

    Just today I tested another of them John Deere radial piston constant pressure source pumps I had already described here. As I was re-reading the article I'd written quite a long time ago (I published it in February on this site, but it had existed for more than a year), besides many grammatical errors (sorry about that!), I noticed that I'd completely forgotten to mention a very important detail concerning these pumps, an error I am correcting in this add-on.

    The very important difference of these pumps from "normal" radial piston pumps, is the fact that they must work with a pressurized suction line, which is the main reason there are two "suction side" fittings - the suction side of this pump is, actually, inside the return line of another transmission pump, which due to the existence of a radiator and a return filter gets pressurized to a minimum of 2-3 bars during normal operation. The suction check valves have springs, while common radial piston pumps have free floating balls or use weaker springs.

    It is very important to create "pressurized" suction line conditions to test these pumps, because the suction line checks weren't designed to work with atmospheric pressure oil. The pump will cavitate, and you might come to a wrong conclusion about the pump's efficiency if you don't find a way to "boost" the suction line.

    One more thing - there definitely is an eight piston model around, which, by the way, has max. displacement of 24 cu. cm.