Complex sentence: In simplest terms, the engine is brought up to the desired RPM and the valve is incrementally closed and as the pump's outlet is restricted, the load increases and the throttle is simply opened until at the desired throttle opening.
Split into simpler sentences: In simplest terms, the engine is brought up to the desired RPM and the valve is incrementally closed. As the pumps outlet is restricted, the load increases and the throttle is simply opened until at the desired throttle opening.