I have had good luck with my UP6 brake valve. By the way, it isn't truly proportional. If you hook up your pressure gauge to it, you can see the pressure levels plateau at certain pressures, example, 0, 20, 40, 60, 80 psi... I don't know exactly what pressures it stops at... I've got mine put on a 3 posn switch, for off, partial, and full.