Open Center and Closed Center, in my opinion or tow nearly useless terms when it comes to describing the hydraulic systems on modern tractors. Reason being, nearly none are truly an open center system and none are truly a closed center system... so it would depend on what tractor you're looking at.
I'm not really familiar with the plumbing on the newer Deere's that claim to be open center, but I'd suspect that it would range anywhere from tandem center to a fixed displacement load sensing type.. Ford used gear pumps in a fixed displacement system, using closed center load sensing valves AND an unloading valve to unload the pump(s)... so they technically class that system as 'open center' because it's fixed displacement. NH used that right up to the end of the TS series on the basic spec tractors.
What you commonly find on high spec tractors today is a CCLS system (Closed Center Load Sensing) which is a variable displacement system with the exact same spool valve that Ford used which sense load. They're also known as PFC (Pressure Flow Compensated) hydraulics. The main difference between PFC and the old Deere closed Center system is that the Deere must go to high stand-by to destroke the pump. The PFC system is normally destroked (low stand-by) until it senses load. When load is sensed it strokes the pump sufficiently to maintain the pressure differential in the pressure/flow compensator valve so it's never pujmping more than is needed at ANY MORE pressure than is needed. The old Deere system simply sensed a leak when you opened a valve and the pump would stroke fully with the goal of overcoming the leak... which is why they're not so well regarded in some circles. They do develop leaks over time, which can be hard to find... and cost money to fix. Not fixing them leads to overheating of the oil. PFC systems are supposed to be less prone to such problems since they're not under pressure constantly.
With all that said, personally, if i was buying a new tractor today I'd be going to a CCLS/PFC system. I have some need of it on a Deere harvester with it's on CC valve bank... and yo neve know what you might buy down the road. It won't hurt you to have a higher end system then you need today, however... for what work you list, the 'open center' system will work just fine. I'd also suspect that from a fuel efficiency standpoint the open center system will generally be more efficient. The CCLS system has all the parts of the open center system that draw power, plus the variable displacement pump which draws more power to turn... so for basic use the OC system is mroe efficient. For heavy use with multiple circuits and less than full system demand the CCLS system will be more efficient because it doesn't need to dump oil to sump at pressure the way that the OC system does. Confused yet?
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Today's Featured Article - Oil Bath Air Filters - by Chris Pratt. Some of us grew up thinking that an air filter was a paper thing that allowed air to pass while trapping dirt particles of a particles of a certain size. What a surprise to open up your first old tractor's air filter case and find a can that appears to be filled with the scrap metal swept from around a machine shop metal lathe. To top that off, you have a cup with oil in it ("why would you want to lubricate your carburetor?"). On closer examination (and some reading in a AC D-14 service manual), I found out that this is a pretty ingenious method of cleaning the air in the tractor's intake tract.
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