Hi my name is Ross, I'm a car technician and I’ll help with your question.
If your van has ABS the ABS modulator will take care of the load compensation and prevent locking so its quite possible it doesn't have oneDo you know what parts exactly have been replaced so far?
If this valve is the problem... where is it located.... how can i find it
The ABS modulator is located under the bonnet, if you follow the brake pipes from the master cylinder you will find it, its a silver/black box with several brake pipe connections and a wiring connector. These can sometimes be problematic, often they can trap air too, its best to bleed the brakes with the ignition running if that's the case. Im not sure what parts the mechanic has replaced, but he should fit brake pipe clamps on each flexi hose to rule out individual calipers/cylinders, if its still spongy, it could be air trapped in the ABS modulator, or a faulty master cylinder. Even servos can cause this to an extent. If the brake servo is located on the passenger side, ensure the linking rods are OK and the pedal box and rod supports are not flexing on brake pedal application.