It's normal for loaders to drift down. When you have 900 hours on your excellent new tractor instead of 9 hours I bet you will have figured out that it is just one of those things we live with.
Since it is a new tractor, here are some things to think about.
All loaders drift down - especially when the loader is "loaded" and just sitting there. And the older they get the more they do. For some reason - maybe complexity - front end loaders (FEL) tend to drop much faster than 3pts so you notice it more.
Most shop manuals give figures for what drop rate is acceptable. It's usually given as inches over so many minutes - and it may surprise you just how much drop rate is allowable. I've seen a foot in 10 minutes given as acceptable - though that would be outside the limit for most of us.
We don't know if it is air. Or to say it another way, nobody really knows how much of the drop is due to air - if any.
As you read through hydraulic literature - and the discussion here on TBN going back years are pretty good too - then there are lots of opinions about air in the hydraulics. Opinions mostly and very little fact. The predominant opinion is that there must be some air, but what there is doesn't need bleeding because it doesn't have much effect on hydraulic operation. Many believe that the movement of hydraulic fluid circulating through the system pumps the air out of the system pretty quickly. Everyone agrees that moving the FEL though all its motions would help - but with little evidence that it did. Still, it can't hurt and I do it too.
Ultimately, what air that is moved by the hydrualic fluid goes to the sump and is expelled via the sump vent on all open hydrualic systems. 99+% of all compact tractors use a similar open hydraulic system and what is true of one is true for all. In fact, a lot of FEL parts are surprisingly interchangeable on similar size tractors.
Bottom line on air is : We don't know, but most believe there is either not much air or if there is lots then it is trapped somewhere that it doesn't have a noticible effect. There is some evidence that sunshine or cold changing the sizes of the hydraulic hoses probably has more of an effect.
But loaders arms do drift down, and buckets do droop. Sometimes slowly and sometimes so fast you can see it happen. So if it isn't air, it has to be fluid escaping - but where is it going? Well, one of the most probable paths is for the fluid to be making its way back past the sliding spools in the control valve, out the return hose, and back to the sump.
BTW, if that fluid leakage path is real, it shouldn't be all that difficult to measure. But I've never seen anyone measure the fluid flow through the return line with the tractor just sitting. So until someone does, we again have opinion but without facts.
So it might be internal leakage in the control valve. After all, hydraulic cylinders can easily be designed to seal with internal O rings - but the operator control valves use machined inside surfaces rather than O rings.
And we know that control valves have some internal leakage. The amount of bypass leakage in a controi valve depends on how accurately each spool valve fits in the bore - and that may come down to care & expense in manufacture. Improving the control valve is one real obvious place to either improve the system or alternately to save costs. Tractor manufacturers rarely make their own control valves. They are pretty universal parts that can range from a few hundred bucks to thousands for a control valve with the same basic specs, mounting, and ports.
BTW, something to think about is there are hydraulic systems with zero leakdown. High lift forklifts and hydraulic cages for lineman to work on electric poles have zero leakdown. They will typically have some sort of positive manual or solenoid valve in the circuit to prevent any fluid movement at all. In fact, tractors have that too. Most tractors have a control on their 3pt lifts that can be turned in to regulate drop speed. Turn it all the way in and the 3pt will hold an implement up all day. You could do the same for a FEL.
Also, many FELs have a third function valve for accessory hydraulic implements that is solenoid controlled. Some of those are zero leakage.
So enjoy your excellent new tractor and learn its habits. Never leave a load in the FEL suspended in the air. If not using it for half an hour, put the bucket down on the ground or lower it onto a stump.
I use mine hard, but never quite completely trust it.
Good luck,
rScotty
