1st thing to establish is whether it is a proportioning valve or PRESSURE DIFFERENTIAL valve. The PD valve does nothing more than turn on the brake warning light if there should be a loss of pressure to 1 side of the system. This is a common misconception that started many years back
This is also the valve that cuts off the low pressure (leaking) side. This is the valve that gives you the dual safety factor. Without it, you don't have a dual system.
