The ASCO Series 551, also known as 8551, is a line of 1/4" 3-way and 4-way compact solenoid spool valves that are ideal for controlling air or inert gas in challenging environments. The valves’ unique design combines hard T-seals and flexible O-rings that provide bubble-tight shutoff, dirt resistance, and multi-million cycle reliability. The 551 Series comes in anodized aluminum, brass, and stainless steel bodies with ¼-inch NPT and BSP connections. It is suitable for the harsh conditions found in chemicals, refining, food & beverage applications and life science processing.