Komatsu Pump from PC240
Hydraulic pump overhauling is a delicate procedure which resembles hospital visits. Sometimes you have planned routine check-ups, sometimes – emergency 911 calls. This particular overhaul could pretty much be described as an urgent reanimation with elements of miraculous resurrection.
Very unknown and very protected, this mysterious Komatsu was brought to my shop by a man claiming that after two odd weeks of extensive diagnostics the OEMechanics came to the conclusion that the machines problem was pump-related and kindly suggested him an option of buying a new pump. No need to say that the price made his hair move, so an alternative solution had to be found urgently as this was a crucial piece of equipment for the hole construction site.
Every time I get a Komatsu (or Caterpillar, or any other protected brand), I get a warm feeling inside. First, because any so called protected brand pump represents a nice back-engineering puzzle, and second, it’s always a chance to kick them in their over-protected nuts.
Don’t get me wrong, I don’t think that Komatsus are bad. Quite the opposite, actually, very efficient, fuel saving, comfortable, innovative, computerized, you name it. It’s that I happen to judge machinery from the point of serviceability, simplicity and availability of spare parts for the machine’s hydraulics, that’s all.
Please note that there is no protected information disclosure here, only my own thoughts of how the stuff works, (which, by the way may be wrong).
I have absolutely no information about the model reference, only some casting numbers seen on the pics, which I am not sure identify anything at all. I do know it came from a PC 240 excavator, so chances are this one is a proud part of a Hidraumind super patented system presented so well in Komatsu’s brochures. Yet another reason to gut it up from head to toes.
Here is what I came up with after an hour of spraying and marking:
It is an open circuit double pump with closed center load sensing and torque limiting control (sum of both pumps), equipped with two proportional solenoid valves (pressure reducers) which allow to override torque limiter setting and load sensing delta P setting. That’s it. A good example of how a scary unknown protected pump turns out to be quite simple after all. For the proportional valves to work you must supply them with a pressure feed, I used 35 bar during testing, worked just fine. The valves will need around 500 ma to fully open. The more the current, the lower is the torque setting, or the delta P. The second pump is a classic closed center LS control, where the delta P is measured between the pumps outlet and the LS signal port. The first pump uses the same spool assembly (pic.7), but the “outlet side” of the spool, instead of being connected to the pump’s pressure port, has an external connection, which means that delta P higher reading can be taken at a remote point. Why? No idea without seeing the actual machine, which I haven’t. Maybe to exclude the influence of the long hose connection between the pump and the distributor on the delta P due to the hose losses. I have some ideas but none making too much sense so far. At least I know what the pump’s control is supposed to do and was able to prove it during testing.
I found the design of the control very interesting, with the whole torque limiting assembly “hidden” inside the servo piston. A neat idea, though completely over-engineered from my point of view. Japanese engineers have their ways to make simple things complicated, but hey, their right, right? I liked oversized o’rings compared to earlier models, which probably solved at least partially leaks problem, typical to Japanese 1000o’rings designs, so prone to oil leaks after several thousand hot hours. Rotary group almost perfect, with Linde-like piston shoe design, compact and efficient, (yet more expensive to produce).
If I was to design a Komatsu pump, I would probably maintain the rotary group but would have at least tried to simplify the control part. I must admit here that this particular model turned out to be very compact for a double, hundred odd cc pump (test showed around 130 cc max displacement), so at least here Komatsu engineers drastically improved earlier designs. These pumps (as well as machines) have Japanese quality on their side and protected designs against them. You should be well aware that most of the times you will have to “turn to the source” when in trouble if you use Komatsu. I personally wouldn’t buy a Komatsu, BUT, I DO admire many new and innovative technical solutions they find, and absolutely sure at least half of their claimed patens are, actually, something new AND useful.