Old School. New Tech. The new 500SE utilizes a servo controlled valve to provide precision airflow and unparalleled performance for both air and trimix divers in a side exhaust configuration. To achieve this, we have perfected the original "lever-servo valve" we designed 35 years ago. Overbalanced diaphragm first stage also provides ideal hose routing for both backmount and sidemount users and optimum performance regardless of depth.