Priority flow control valve

[John C.]

Closed center hydraulics have all the center ports blocked and are most of the time three position. There are two position valves for things that are simply on or off. The park brake in a loader is usually set up that way. The example shown is a closed center valve. All ports open is referred to as a motor spool. Usually there are straight lines that designate the sections of the spool. What is hard to grasp sometimes from a line drawing is that there are cut outs in the valve spools that smooth the transition from no flow or center flow to one direction of the other. The page above probably shows the concept but It comes out too small for me to see it. On yellow iron I've never seen it in a schematic. Service manuals usually explain it but don't provide some kind of graphic to make the function easier to understand.

It would be nice for each line drawing to have a legend the one that maytag shows above.

 

[maytag]

I didn't clear much up with my download. using a new computer system that is supposed to be a combination of the best features from the Mac and Windows but there is a steep learning curve for me. Anyway Rexroth is good to provide the details like this.
Never seen one of these symbols used on a schematic but info is useful in design and especially failure analysis. I believe that was what the engineer was trying to convey on the print the original poster provided.

 

[WEA]

Not sure which question you still need an answer to.
For the Reverse modulating SAHR brake pedal, the check valve is for reverse free flow. ie; when you dump the supply, you dump everything downstream, and the brakes apply.
Basically, the valve is a pressure reducing valve, which was how we originally drew them when designing the systems. There is no real ISO or ANSI symbol, so all the folks at Mico, Rexroth, Wagner, and all, sort of took some liberties, and made up their own symbols.... more or less. They threw in the lines for 'sliding spool' among other things, but they do make sense if you gaze at 'em a bit. Compare it to a run of the mill PRV with reverse free flow. It'll make more sense.
(attached is ISO of PRV with reverse free flow)



Bill