IMO, pushing on the shaft only increases the pressure on the piston seal, that is under spring pressure and seated and holding off flow. As the brakes are applied the rear brakes see pressure first, as pressure increases to about 40psi it overcomes the spring pressure in the ROUND HOLD OFF VALVE. Fluid flows into the line at the big nut , passed the piston seal, out the side fitting to the distribution valve, to the front brakes. Sometime watch the shaft move out as the brakes are applied by a helper.
If you wanted free flow through this valve it seems to me one would pull and hold the shaft open to unseat the piston seal.
Open to learning more if this sounds incorrect to others.
Mike
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04-05-2020, 01:01 AM
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