The amal valve is a way to help boost rise quickly at the beginning of boost build up.

At lower boost levels the amal valve is powered by the ECU and the boost from the compressor diverted to the airbox, hence allowing the boost to build quickly. At a certain level the power is taken away and all boost will be going to the actuator.

Without amal valve boost would be going to the actuator from the start, the actuator spring will give way and start opening the waste gate a bit from the beginning of boost. In this manner it will take longer to build boost.

This of course applies to a standard set up. A -31 actuator with a much stronger spring than standard, will give way to the boost pressure later.

Cheers