To better understand the following technical description, please look at the three pictures above.
Through the filter box air intake, the air comes to the intake manifold before the VOLUMEX compressor. In this point, just before the supercharger, cold water is injected to reducing, by vaporization, the air temperature increase due to the compression supplied by supercharger. The volumetric compressor is provided with two different outlet sections. That lower is connected to the first intake manifold piece and, through the second piece, to the air throttle valve. The third intake manifold piece brings the fluid to the pipes inside the 16 valves head. The upper outlet section is connected to a long aluminum pipe and at its end there is the POP-OFF (or BLOW-OFF) valve.
This device is to discharge the air flow when the engine is running at high rpm but with the throttle is on idle (that is in phase of release) and in all the situations where the depression after the butterfly valve overcomes the rigidity of the contrast spring in the device; the prupose of this is to avoid the ram phenomenon to the volumetric compressor.
The supercharging maximum pressure is adjustable acting on the pre-tensioning of the spring inserted in the overpressure valve, sets in the central part of the intake manifold - piece 2. Contrarily to the WASTE-GATE valve, present on the turbocharged engines, the overpressure valve only works at the most elevated rates and at the full butterfly valve opening. A very short pipe finally send the outgoing air flow from the POP-OFF valve to the gearbox oil cooling system.
Another overpressure valve also fits out the 3rd intake manifold piece; in some situations (for example when throttle is suddenly and completely opened and the engine is at a low rpm) flame and blast can let in the intake manifold. This means a very high and fast pressure increase into the intake manifold (it's a pressure wave), that can seriously damage the compressor's blowers. This is why this overpressure valve is placed close to the combustion chambers; however it works at a higher pressure value than the supercharging one.