When connecting the hydraulic hoses on a vacuum planter to a tractor, be aware the hoses that power the hydraulic motors that run the vac fans need to be connected "backwards."
The reasoning for this confusing situation actually makes sense when you understand what is going on: Vac fans spin at high speeds. It can damage the motor on a fast-spinning vac fan if oil flow to the fan is stopped abruptly.
Most tractor hydraulic controls are set up so that pulling back on the hydraulic lever in the cab raises equipment and pushing the lever forward lowers equipment. The "neutral"position between raise and lower immediately stops and locks all flow of oil. Because vac fans spin at such high speed, they don't like to stop suddenly, so it's best to not shut off a vac fan motor by putting the hydraulic control lever in "neutral."
The solution is to reverse the way the vac fan hoses are connected to the tractor, so that pushing the hydraulic lever FORWARD sends pressurized oil to the vac fan motor. To shut off the vac fan, the operator pushes the lever another click or notch forward and locks it into "float" position. "Float" allows oil to flow freely, without pressure, so the vac fan can freewheel to a stop without damaging the motor.
In order to use "float" position to shut off the vac fan, the hoses connecting the vac fan to the tractor have to be connected so that the pressure hose to the vac fan motor is in the return side of a particular hydraulic coupler on the tractor, and the return hose from the fan is in that coupler's pressure side.
Confusing, ain't it?