Hey Guys, Happy to be a new member here... have a question about bobcat hydrostat. There seems to be alot of informaton about the charge pressure in a bobact track loader on the net and what its used for, my question is where is the charge pressure generated for instance on a bobcat 864, the machine (according to the display and indicator lights) has 0 charge pressure, the boom will not operate and the brakes on the drives will not release, now i realize that this could be as simple as a bad sender or plugged filter but im trying to play out the worst case scenairo in my head befor i get started. Does the Aux pump generate charge pressure for the Hystat pump group? or does the hystat pump generate its own charge? pretty sure there is no engine mounted charge pump like you would traditionally see on a larger machine (cat)? any input would be greatly appreciated!!!
Welcome to HEF DieselMD. I don't have any books on the 864 so I can't say for certain, but most Bobcats of that vintage, the charge pump (or work equipment pump) is a gear pump that piggybacks off of the hydrostat drive pumps. It draws oil from the reservoir and sends it to the main control valve for loader functions. Oil passes through the main control valve, then goes to the hydraulic filter and oil cooler. Once it leaves the hydraulic filter and cooler it goes to the hydrostat drive pumps to "charge" the drive pumps. Excess oil not needed by the drive pumps returns to the inlet of the charge pump to repeat the cycle, it's a closed loop oil system, not a "return to tank" system. That the simple story of how it works.
the 864 has it's charge pump internal to the hydrostats, it's between the 2 drive pumps. the hyd pump is piggyback mounted to the end of the hydrostats. so, no drive & no hyd? have you checked the drive belt? :drinkup
See, I knew better than to say for certain about the 864, thanks for the clarification crewchief. :notworthy
the external charge pumps didnt appear until '07 (?), i'm not sure on the date but it's around the time K series machines. K series machines had hyd driven temp controlled cooling fans... :drinkup
Yeah, took me a while to get used to those things when they first came out. Be working on one with the engine running, hands working in the innards of the machine, then the fan kicks in, scared the bejesus outa me!
Ha.. ^ I am pretty new at the Bobcat Tech thing (been mechanic'ing things as all Farmers do for ~30yrs though) and the first time I had our T190 running with the Cab flipped up, and it was warmed up, THAT ^ happened and I likely said what you said too.. Heeehaw!!
Well, I did use a few choice curse words that I can't repeat here because the auto sensor would wipe them out.
Ha _ NO Doubt _ I remember I straightened up and 'hit my thinly covered head' on something under there, but not too badly at least _ Quite startling though when nearby!!