Komatsu PC 40: somebody told me when changing your hydrolic fluid you have to pressurize your tank. never heard of this. is it true? if so how do i do that?
your tank is already pressurized until you release the pressure. They probably said depressurize it before you pull the drain plug. Seen that done before its pretty funny.
Used to own a 1988 PC-40-6. Manual stated to loosen the fill cap slowly while rocking it to release pressure. Make sure all implements are on the ground and have no residual pressure on them.
Check your operator's manual. MANY Japanese mini excavators use a sealed and pressurized hydraulic tank. After tank or filter service, you need to, at IDLE, Cap loose, raise the boom fully up, arm in, bucket in, tighten the cap and go to work. Failure to do this in winter with a hammer in particualar is a disaster for the main pump. Kobelco tried it 10 years ago and changed the US specification to a self presurizing system.
What system or systems is used to pressurize the hydraulic tank in general? Is it mostly Jap machines that use hydraulic tank pressure? Drag1lines post suggests that the tank cap is put on when the tank fluid level is at its lowest and this will cause air in the tank to be compressed and provide fluid pressure when fluid flows back into the tank. If this is the way its supposed to work or is some other pressure source used?
Takeuchi also uses this system..or did within the last three years. Kobelco did 12 years ago, but since then is self pressurizing for the North American market. With the oil level low and cap open, the tank will pressurize after the cap is closed and the attachment lowered. Now, in warm weather, over time heat will cause the tank to pressurize and remember, we are only talking about less than 10 psi. The problem is winter, cold oil and hammers, which do not cycle the oil level. Yes, this is how it is supposed to work. Again, in all instances, look at your operator's manual to be sure.
American machines used to have a compressor specifically for pressurizing the hydraulic reservoir. This came about with the use of rotary piston pumps. They pump real well but they do not suck oil and need something to push the oil into them. The compressors caused lots of problems over the years. Putting moisture in the tank was probably the worst situation but I've also seen the compressors not cooled properly, throwing a rod and running the engine out of oil. The Japanese excavator manufacturers eliminated the compressors by using what is essentially a radiator cap. When you extend all the cylinders the level in the hydraulic tank goes down. The cap lets air into the tank. When the level goes back up because you retracted the cylinders the air is trapped in the tank. The same thing happens in the radiator of your car. The only thing you need to do is cycle your cylinders before each shift and you are done. The reservoir pressure generally runs anywhere from 7 - 14 PSI. Problems usually happen because the maintenance staff does not know of the problems associated with the cap. If you crack the cap at the end of the shift and you don't get any air, you need to fix the problem. When the seal goes bad on the cap, your tank does not get pressurized and now your pump begins to make noise. Let it happen long enough and the system gets hot and the noise gets louder and the pump life gets shorter. When you change hydraulic oil there will be air trapped in the pump and the pump has the chance of running dry before oil finally gets in to lubricat the surfaces. On all Komatsu excavators there are bleed screws in strategic place that let you bleed the air out. It takes awhile so to hurry things up many times I would put four or five pounds of air on the tank with my compressor. Once you have the air bled out you can start the engine. Don't move a function though because you will still have air working its way out. Crack the bleed screws a little at a time till you get no more air. Then you can start moving things easy. Be carefull now when you open the tank cap to add oil because all the air working its way out of the system ends up in the tank and really pressurizes it. Good Luck!
Ok, now were are talking about large machines, not mini's. Yes, early American manufacturers did use engine driven compressors and electric compressors to pressurize the tanks and so did earlier Japanese manufacturers. This was an additional complex system. One US manufacturer actually used large gear pumps to supercharge the main pumps. Kawasaki, ONLY on the larger pumps, KV180 and larger, now uses an impeller pump in the center section of the tandum pumps to suck and push oil into the main pumps, but the tanks are still pressurized. The need for this was that manufacturers began to, like every thing else, push the pumps harder for more flow, with smaller pumps, and cavitation could result.