Yes, it makes sense Cmark as obviously we can only discuss possible theories of operation since we're not privy to exactly how that priority valve is operating. Genie uses a similar priority valve on some of their aerial boom lifts, but they're more like the Parker illustration, an input, a priority output, and a secondary output that receives flow/pressure after primary priority circuit is satisfied. The fourth line in this one I've not seen before and can only guess what it's doing, especially since the priority output and secondary are pressure compensated and the fourth port circuit is not. Really weird valve.
I get what your saying about pressure changes, especially rapid drop in pressure on brake circuit and how it would affect charge valve, but don't forget about the adjustable spring on the charge valve forcing the spool to the left thereby putting it in the blocked outlet to tank position. Also, the .020 orifice is going to always have the sensor line lag behind the pressure changes in the brake circuit.
Additionally, we don't know what pressure that charge valve is set at to overcome the spring pressure and dump pressure in the sense line to tank. What we can tell from the drawing is the oil goes to the fan motor, then it returns to supply the pilot circuit and to a designated relief valve set at 350 psi. By reason of that relief valve we can assume the pressure returning from the fan motor is below 350 psi, otherwise the relief would always be cracked open creating heat. This, of course, assumes there is not some other form of pressure regulating valve after the oil leaves the pilot lines of this manifold drawing.
Assuming this is correct, that's what prompted me to think the charge valve is operating as a pressure regulator, keeping pressure below the 350 psi of the fan motor return circuit relief valve.
Very peculiar circuit for sure.
