There are actually three types of self levelling:
-Mechanical self levelling
-passive self levelling (Another hydraulic cylinder under the lift cylinder, communicates with the tip cylinder to self level
- active self levelling (a valve is actuated whilst lifting, letting pump pressure sucked into the tip cylinders)
hydraulic self levelling by means of a valve, wastes energy: To lift it you need a high working pressure: relieving the oil into the tip cylinders is allmost vacuuming it in:
The difference in pressure is power you waste, as a part of the full pressure pump flow is drawn through a restricted valve, which turns the pressure into waste heat.
The loss is comparable to non self levelling loaders.
Both hydraulic SL by means of a reaction cylinder, and MSL, roughly increase the lift force by 20% as the center of gravity of the load, is lowered when you tip the bucket forward when correcting: When self levelling does that on the go, you're only putting in as much labour as required: Not first lifting it up, while releasing this kinetic energy by tipping out the bucket to keep it level.
So, 20% more lifting force with general attachments (or no energy loss) and this gets even more when working with e.g, a boom pole: Without it, you have extended the force x arm by two, if you hung a 3 meter boom pole on a 3 meter loader arm.
With self levelling, the hook moves parallel to the quick attach hinge point on the loader boom: So with the same lifting cylinders you'd be lifting over the same 3.5 meter height, no matter how long the boom pole would be.
Just one disadvantage of self levelling: As it uses geometry to do this trick, it only works 100% in the bucket or implement position it is laid out for: Tip your bucket fully out, lift it and you'll see that in a 90 degree rotated bucket position, the bucket waves all over during lifting or lowering.
JD had a flip-over geometry arm, (in the turnover triangle in the bend of the boom) so you could change the parallel arm geometry for A. a horizontal pallet fork and B. a full dirt bucket, tilted 45ー back so it doesnt spill when lifting.
Industrial loaders dont need this as they have flat booms, so the cylinder angles in fully tipped back quick attach position are good enough to hold that pallet fork, in the same position as a fully tilted back position.
On tractor front loaders with curved booms, the cylinder stands more upright, decreasing the hold force when the bucket is rolled back: thats why loader manufacturers make pallet fork frames with a QA angle which is putting the tip cylinders out of their dead angle, and make the parallel position accordingly...