Engine speed and 3PH lifting capacity...

[MHarryE]

The relief valve on your system is a direct acting relief. A spring presses on a poppet and when the pressure is high e ought, it lifts the poppet allowing oil to flow back to tank. If you increase the flow rate it needs to lift the poppet higher and therefore the pressure increases. If you look at hydraulic supplier catalogs they often have a flow vs. pressure chart. So you will be able to lift more at high idle, but will it be enough?

 

[GManBart]

The load will lift slower at a lower RPM because the flow rate of the pump will likely but much less at a lower RPM than a higher RPM. but the pressure that can be achieved will likely be the same.

In a closed system like this (fairly simple setup), pressure is directly related to flow rate. Higher flow rates equal higher pressures, because the amount of resistance/restriction, (or potential resistance) remains constant. In other words, if you raise the 3pt lever, the valves are at the same setting regardless of flow rate. If you increase the flow rate, the pressure will increase, up to the relief setting. In a complex system it would be possible to vary valve setting/controls based upon flow rate, and have multiple pressure relief settings, etc, but that's likely far beyond anything seen in normal tractors. If the pump can produce max flow at idle, then the system would almost always been running with the relief open somewhat. It would be interesting to see what RPM produces max flow rate, but I doubt we'll ever be able to figure that out. I'd guess something like 50-60% of rated speed for max low rate.

Anybody know if the Nebraska tests covered that?

 

[OldMcDonald]

I am a McDonald not a McAnic, so I learn something new almost every time I lurk around TBN, but special thanks to you all for today's lessons.

 

[adirondackmtnman]

I am a McDonald not a McAnic

HA! That's clever!!!

Sent from my LGL35G using TractorByNet

 

[Stonehaller]

The short answer is running the engine at rated or max engine RPM will give you slightly more lifting capacity.

Your pump is positive displacement so each revolution of the pump generates the same volume. The faster the pump turns, the more flow it generates. The more flow, the faster a cylinder will move. Pressure equates to how much force it takes to move a cylinder. The more load on the cylinder the higher the pressure. The relief valve limits the maximum pressure and therefore the maximum load the cylinder can move. The relief pressure is mostly independent of the flow. Two good points raised here by others (SPYDERLK & MHarryE), internal leakage takes some of the pumps output and the poppet relief valves have some non-linearity with flow and oil temperature. High flow and cooler oil will give slightly higher relief pressures. To get the maximum lift capacity, run the engine at rate speed and do the heavy lifting before the oil gets hot.

If suprnova is correct that your lifting capacity is 1058 lbs at 24 inches sand you cannot lift 883 lbs, then you may have other issues. But first, is the center of the 883 lbs within 24 inches? (Pictures are nice) If the center of mass of your attachment is beyond the 24 inches, then you may be exceeding the lift capacity.

Are there multiple holes for the lift rods to connect to the hitch arms? If there are, you may need to move them further from the tractor. That will reduce lift height range, but increase lift capacity.

Your signature says you have a backhoe. Do you switch a valve or connect a hose loop when the back hoe is off? Double check that you have that correct and quick disconnects are fully seated.

Your relief pressure could be low. You would need a gage and a fitting to connect the gage to your backhoe supply quick disconnect or one of the FEL quick disconnects. If it is low, you will need to get the relief valve adjusted.

You could have an internal leak in your 3 point cylinder or valve. Will it hold up a load with the tractor off? Note that the 3 point speed control only affects lowering speed and has nothing to do with raising or lift capacity.