https://www.avtecdental.com/mini-fix...-dci-9155.htmlI had an idea , using one of these as a pressure regulator for brakes before brake valve. That way I always would get a max 35 psi for brakes and still could use 100 psi for rest of the system.

doable?

not very expensive but shipping is 25$ to europe..
And looks small and lightweight solution.

Seems like adding the brakes to the gear circuit introduces more potential for gear failure. I can live w/o brakes. But if the brake valve fails, I can not live w/o gear. I just thought separating the two is the safest for the plane and why would anyone combine the two unnecessarily introducing more risk to the critical gear system.

Get a UP-6 brake valve and you can control the brakes at any place you want to. Mix the brakes in with the down elevator when the gear is down and you are not fumbling around for the slider. Set the servo travel on the brakes in the Mix so that they can't lock up. My small can of air and the UP-6 gives me at least 30 flights before I have to refill the air. Also put the brakes on the slider so that you can lock them when starting, etc. KISS

+1 for the UP6.

Plumb your gear to the down side air for your retracts. I have done this for years and brake leak(which I have never had) wont drain your gear until the gear is down.

If you have never experienced a brake failure, how do you know they will actually lock before the air is gone? I suppose it would work if the gear snapped down quickly. I have one plane with orifices in the gear air lines and the gear come down slowly. But it has a separate systems. Air tanks don't cost that much these days.

But that is a good idea to minimize the risk of tying the two systems together. Learn somethin' new everyday.

I am using Xicoy and jettronics valves, so I do not need UP products. I have not had any problems earlier with combined systems and I do not expext them now either.

Usually the leak is from air cylinder or supply intake..

Personally I do not like using a slider for brakes. I have set up a 3 way switch with parking brake at low position and springloaded up position is at different value which gives lower breaking power to keep wheels from locking.
Slider just does not feel ok to me for using. Now, if we can always get a constant pressure for brakes, its easy to set up brakes not locking with Xicoy valve as it has a pulsing option.

And of course I have mixed channels so it prohibits brake and steering when gear up selected. Also gear up selection is prohibited when engine switch is off, just to prevent accidental retraction while servicing the plane.