Hydraulic pump vs motor sizing

[daveyclimber]

Just had some questions about some of my forestry mulchers. One machine has a 100cc pump running a 160cc variable motor. Another machine has a 130cc pump running 2 130cc motors.
Im just trying to understand the physics of running a pump with less capacity than the motor or motors. How does this work?

 

[Delmer]

Just like 2nd gear in a transmission, the output is slower than the input. Typically the engine spins faster than you want the final speed to be, so the size of the motor is a balance between making it bigger/costlier, and smaller with other speed reduction.

 

[Tones]

Like Delmer says. Easiest way to understand it is to think of it as a gearbox. Small gears driving big gears produces more torque and vice versa.

 

[John C.]

The only thing you give up by running a bigger motor with a smaller pump is the turning speed of the motor. Used to be a problem with log processors. I've seen a few big processors meant for 30 ton machines being installed on 20 ton machines. The owners and operators would complain about the speed that the rollers pushed the logs through the knives and would use the machine swing to make things go a little faster.