HKS Super Sequential Valve [single + dual turbo models]

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The HKS Super Sequential Blowoff Valve (SSQV)

It is a dual stage pull type relief valve. Unlike other blow off valves that are push type, the SSQV will not leak under high boost conditions or under vacuum when not using. Being of a pull type valve structure, the SSQV can not physically leak under any level of boost because boost pressure also keeps the valve closed against its seat. The SSQV is actuated by pressure alterations only, not by the rate of pressure or vacuum in the line, which ensures a quick valve response and complete closure during idle.
On typical blow-off valve designs, a large valve is utilized in order to accommodate high boost / high horsepower applications. However, these large valves tend to react slowly and require high activation pressure to open, therefore are not able to activate and prevent compressor surge at light-load conditions. On the other hand, smaller, fast reacting valves do not discharge the airflow capacity required for high horsepower applications and tend to creep open and leak as the boost pressure overpowers the spring on these push type valves.
For maximum performance, the HKS SSQV incorporates both a small primary valve for ultra quick activation, along with a larger secondary valve for additional discharge capacity. The SSQV is engineered to initially open the small primary valve at light throttle and load conditions, then sequentially opens the secondary valve for additional relief capacity under high boost and load conditions. The SSQV is constructed of polished billet aluminium, which ensures long-term durability and visual appeal. The triple-fin discharge port design produces a powerful and unique aggressive blow-off sound along with added visual distinction. (info courtesy of HKS USA site)