Mini Excavator Hydraulic pump Swap

[racerboy832]

I have a Older Mini Excavator with a Variable Displacement Radial piston pump on it. It is a 2 Section pump with small gear pump on end. I've priced out rebuilds from anywhere from $2000-5000. My Question is, Why can't I just bolt a regular 3 Section Gear pump on it like they use on the Bobcats,Loaders, backhoes Etc... I see them new from $500-800. Some of the older machines had them from the factory.. This is just a Yard machine. I just got the new Surplus center catalog and it has me thinking...

 

[bigdeano]

If you have a closed center hydraulic system the pump has to stop pumping when pressure reaches a certain point, and change it's output to match the gpm demand of the function you're using. Gear pumps don't do that. Better check on what you have now to see how it works.

 

[mrmikey]

I have a Older Mini Excavator with a Variable Displacement Radial piston pump on it. It is a 2 Section pump with small gear pump on end.

Like BD said, it's a closed center system, put a fixed displacement pump on that without a lot of mods, it'll go boom. The gear pump is probably for pilot pressure....Mike

 

[Arc weld]

Variable displacement pumps are more efficient and are usually load sensing meaning they will match output to the working conditions. Lower flow/ higher pressure for hard digging and faster flow/ lower pressure for swinging and dumping.

 

[J_J]

The pump may be a closed loop or open loop hyd system, using a charge pump.

Excerpt:

Charge flow is required on all Series 90 pumps applied in closed circuit installations. The charge pump provides flow to make up internal leakage, maintain a positive pressure in the main circuit, provide flow for cooling and filtration, replace any leakage losses from external valving or auxiliary systems, and to provide flow and pressure for the control system.

The pump on the back of the VSP could also be a gear pump for things like boom swing, and other hyd operation.

The pump on the rear of my VSP is a PTO pump for my steering and loader.

You really need a VSP for smooth machine operation.

If you or someone can't fix the VSP you have, then there are replacement from places like Eaton, Danfoss, etc.

You could use all gear pump, but you would have jerky starts and stops with poor control of speed.

The VSP on my machine is used to power all four hyd motors in a closed loop operation where the out put of the hyd motors is fed back to the input of the pump, with the charge pump making up for any leakage from the hyd motors.

Depending on the shaft type, round, splines, hex, etc, one could replace with another VSP using similar dis placement

 

[racerboy832]

The first two sections are for the Digging and Moving functions. The end gear pump is for the Pilot controls. This is just a cheap beat around the backyard machine. I am a mechanic by trade so a lot of times as many people on here can relate to what seems like a huge problem can be sorted out or refitted. The Manual for this machine is no where to be found. I bought the previous models service guide hoping stuff would cross over but that model uses a 3 section gear pump and thats what got me thinking. The pump is the 13T 7/8 Shaft with 4" pilot. It seems pretty common.