Got a simple question for you guys that are familiar with the Cat line of excavators. Is the propulsion circuit run closed circuit i.e. hydrostatic drive or open circuit i.e. thru directional control valves for each side? TIA Maytag
Through the main (directional) control valve
Thanks for the quick reply. would anyone have a schematic?? I've been asked about adapting a 345 to a special application hydraulic-wise and although have years of heavy industrial hydraulic experience I have very limited mobile.
To get the correct schematic would need the Serial Number prefix of the machine in question. There are about 20 different models of 345, 345B, C, & D models.
Thanks, as things progress I may be seeking some info/help from some of you.
Special hydraulic application for a 345, this has to be good. Post some pictures if you have a chance.
Excavators as a rule spend much more time digging than they do travelling (Or at least they're supposed to) so they use open loop (not to be confused with open center, though some are, but I digress) hydraulics because that's what works best with lots of cylinders. Things that travel a lot like rubber tracked dumpers and make lots of turns like track loaders and skid steers, or need to travel faster, generally use hydrostatic drives. They're more efficient because they run higher pressures and pump the oil around in the closed loops rather than back through the tank each trip. When turning the slow side actually backfeeds power into the pump stack to help out. Open loop travel drives will have a counterbalance valve fitted which only allows the motors to turn as fast as their is oil flow for, if the motor tries to run ahead of the available oil flow, the valve spool shifts to restrict the outlet port providing a braking effect. Hydrostats generally only brake by backfeeding into the engine. So, there ya are, travel systems 101 Lantrax style, LOL
Thanks Lantraxco, I assume the pumps use some type of load sense control, would this be correct??
The load sensing is done inside the main pump head. There is no pressure compensator valve with a signal network from the valves. They also use a negative flow control signal to cut back the pump flow when all the spools are in the neutral position. The ECM controls the pump output according to engine load by using a pilot pressure signal through a solenoid operated pressure reducing valve.
Well another question for you Cat guys. Although this machine will be custom made it will use a Cat 345 "running gear", tracks, finals roller etc. The model they want to use is powered by a Rexroth A6VE160 motor with the BVI counterbalance valve option. I don't have much documentation from Cat SO question is, does Cat also use a negative brake (mechanical set/hydraulic release) in addition to the counterbalance valving?? TIA
Not familiar with that exact machine, but typically each drive will have a mechanical spring applied parking brake, usually automatically released as a function of the counterbalance valve.
Thanks Lantraxco
Yes the travel motors each have a park brake mounted in the end of the motor that is spring applied and oil released.
There will be two small separate external hydraulic lines to the travel motor for releasing the brake and for the motor case drain. This is in addition to the 2 main hydraulic lines for forward/reverse travel.
Nige, what controls the brake release then, solenoid valve, logic valves, or?
I need to correct that. The parking brake is released by oil tapped off from the travel line via an orifice and through the counterbalance valve. The 4th line to the travel motors is the 2 speed travel pilot signal.
Okay thanks. I have seen a variety of systems, but this is I think the most typical.
hi Maytag. here are some prints that may be of interest. I couldn't find a s/n but these are 345C
more prints