They're changing both pressure and flow in those tables, which makes it look like flow has an effect on torque. But you can find any text book on hydraulics to tell you what affects motor torque.
That's right, and so is what I said for any hydraulic system - "More flow will allow it to flow faster, but any flow at all will turn it at full torque minus momentum"
All flow buys you is speed. Think of a hydraulic jack lifting your car. It's flow is very low, but the pressure is still capable of lifting the car. Increasing the flow rate doesn't make it lift any more weigh, it just makes it lift it faster. Pressure provides the force, flow provides the speed.
The charts are misleading because they are advertising charts, not science or engineering charts. Their purpose is to help in comparing products so you know what to expect out of their post hole drills. They had to hold something fairly constant to make a comparison, so they unfortunately chose RPM. For most of industry, speed matters. But or a guy putting in post holes on his land....as long as the speed is reasonable, he cares more about other things.
That is why those charts aren't comparable. They are trying to help you decide, but are using different pressure, flows, RPM, and even different hydraulic motors on the two different post hole drills. That makes it confusing.
If I had hard soil with rocks and dry compacted clay and could stand to to go slow, I'd get the larger one of their drills. Otherwise for lighter soil - like good sandy loam - the smaller one is fine.
Using Post Hole Drills to do fencing on many farms and on our place - all PTO types - what really mattered more than anything was getting an auger with replaceable teeth on the bottom (twice the price!!), and being able to turn the auger real slow with high torque. Plus always wishing the darn thing had a reverse rotation like a hydraulic auger does for when it gets stuck. There just isn't much reason to spin the auger fast.
rScotty
