. ResearchGate +1 Sievers Type 1 (S1): A valve that has one "raphe" (a fused seam between two of the three original leaflets), resulting in two functional cusps instead of three. Significance: Patients with S1 type valves may experience faster progression of aortic regurgitation (leaking) compared to other types. ResearchGate +2 3. Automotive: High-Performance Valves In the automotive world, "S1" often identifies a specific stage or series of engine components: GSC Power Division S1: A popular line of high-performance intake and exhaust valves, often made of stainless steel, used in turbocharged engines like the