Excavator hydraulic pump help ?

[oldnslo]

Is there anyway to verify what type of system I have?

What are the piston pumps connected to? A valve stack that runs cylinders or just the two track motors?

If valve stack running cylinders then you have an open loop, closed center system. My guess is this is what you have.

If connected directly to the track drive motors and nothing else then you have a closed loop system. With this you would have to have another pump to run the excavator digging functions.

 

[racerboy832]

The piston pumps are connected to a bank of spools that each control a function.

 

[wdchyd]

I would think a tandem gear pump would work. One larger gear housing could be plumbed with a flow splitter to two separate open center valves to control the final drive motors, the smaller gear section could be matched up to copy the flow of the existing aux pump, not sure if your existing control valve is usable unless by some miracle the existing aux pump could be mounted to the new gear pump

 

[racerboy832]

How would I know if I could buy a gear pump and just pump it into my existing valve body. The smaller gear pump I can handle. I just don’t want to put a two section gear pump onto my existing valve body and have something dead head or overheat.

 

[oldnslo]

How would I know if I could buy a gear pump and just pump it into my existing valve body. The smaller gear pump I can handle. I just don’t want to put a two section gear pump onto my existing valve body and have something dead head or overheat.

On the existing valve bodies you would have to determine if they are open center or closed center. You might be able to tell by removing the pressure and tank lines and trying to blow air from pressure to tank. If it moves through freely you have open center valves, if not you have closed center valves and they will dead head the pump. With variable volume pressure compensated pumps I suspect you have closed center valves. The big, big unknown is if the valves can be converted from one style to the other. A clue might be if they have a port labeled PB or C for power beyond or carry over.

 

[racerboy832]

I will try that this week. What limits the max pressure on a gear pump. I would imagine imagine if the pump is pushing more than the relief pressure at xxx rpm it would cause a ton of heat.

 

[wdchyd]

I will try that this week. What limits the max pressure on a gear pump. I would imagine imagine if the pump is pushing more than the relief pressure at xxx rpm it would cause a ton of heat.

...........and if it doesn’t have a clear open path in neutral and blowing over relief it will heat, or worse go boom. Do you have any pics of said valves you are planning to plumb the gear pumps for drive?

 

[racerboy832]

 

[wdchyd]

I’m wrong about a closed loop hydrostatic. Like you said It appears that this valve is fed from both ends from your two piston pumps and the common return is the largest fitting in the center, no? A lot going on here, not sure how a gear pump would work unless some sort of unloader valve was used between the gear pumps and control valve.

 

[racerboy832]

So basically what you are saying is the volume of oil coming in from the pressure side would be too much for the return side.

Yes exactly, it’s fed from the ends and returns from the center