For those who are in search for a good brake valve i have the following news:
I just operated the new Jet-tronics no loss brake valve and it is excellent.
Braking is much more proportional than the older PWM valve and it only uses a very small quantity of air.
I never had any servo operated air brake valve so i cannot compare it with those valves like the UP6 but it looks proportional indeed to me.
The quality is very good and right now i left the tank full with no power in order to check for any long term air leaks from the valve and tubes.
I only used about 5 brake applications so far but the pressure remained almost constant (i measured it before and after) , this thing is as close to a no air loss valve as possible i think. It looks like i can now apply brakes many times without worrying of loosing the brakes because of low air pressure.
Service life remains to be seen but it looks like a very robust unit.
Update:
As i read the manual the valve needs some rules in order to work best, not that it is not working very well with my old settings but i can see that it can do better.
It needs that the air lines must be around 2m long (probably it uses them as an expansion chamber) and for best results a dedicated air tank for the brakes
(it says that this is not absolutely required but it enhances the brake operation) filled with just enough pressure in order to have maximum braking when the valve is at full brake position.
It is evident that he tries to expand the range from no brake to full brakes in order to enhance proportionality.
In any case i used my old setup with about 170cm of air lines and 8 Bar (i should use 6 Bar if i was following the recommendations)
of pressure and i was able to program the valve and get very good proportional braking.
It comes close to my hydraulic brakes in proportionality but hydraulic brakes are still better, not much but they are.
Of course with hydraulic brakes you can have a real mess in no time
I really like it[8D]
Chris