Omar may be right.

I have no problem running the fan with the open center system as long as a person uses either A. a motor that is sized for the flow that the tractor pump is putting out which is not the case here (fan motor uses 3-5 gpm and tractor is probably something over 14) or B. a method is used so part of the flow can be directed to the motor and the excess can be directed back to the sump. This is why I recommended using the flow control valve in the link I gave and I have no problem believing it will operate the blower motor properly with no harm to the tractor pump. We have used and I have seen these valves used in numerous applications on open center systems (what they are actually designed for) and closed center systems where the tractor is diverting a portion of the total flow to these valves in an open center fashion. The other problem can be heat generation running a motor continuously if the tractor is not equipped with a transmission cooler which I do not know if this tractor does but all the 4 cyl 5000 series tractors do so (some or all of the 3 cyl 5000's do not) I would assume it does.

But Omar hit the nail on the head when he started talking about an open center system having trouble doing more than one task at once. This is where the trouble will come in. Most likely at best the blower motor will slow when the planter is raised and at worst it will stop, then restart when the planter is finished raising, causing seeds to fall out of the cells and the planter leaving a skip for the first however many feet till the cells get filled.

The method Omar describes capturing the oil between the pump and the tractor valve/3pt most likely involved using a flow control valve to divert part of the oil to run the blower and allowing the excess to flow on to the tractor hydraulics, allowing both systems to operate at once but with reduced capacity to the lift system.

Some open center valves can do multiple functions at once. A backhoe valve comes to mind. The problem is the only way to know how the 6303 valve would work trying to run the blower and lift the planter would be to try it and that may not be acceptable to the owner. At best the blower motor is probably going to slow when raising the planter.

The flow control valve will work running the fan. Running the fan and lifting the planter both successfully at the same time may not be possible.

Sorry for my misleading post and thanks Omar for trying to keep someone from making a mistake.

John