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ASCO™ 551 1/4
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.

ASCO Series 551

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ASCO™ 551 1/4" Solenoid Spool Valve


Valve Actuation
Solenoid - Air Pilot
Body Material
Brass, Stainless Steel, Aluminum
Air, Inert Gas
Pipe / Port Size
1/4 "
Port Type
3 way - 3/2 Normally Closed, 4 way - 5/2, 4 way - 5/3 - Closed Center, 4 way - 5/3 - Open Center
From 0.5 Cv to 1.0 Cv, From .43 to .86 Kv
24 AC, 110 AC, 120 AC, 220 AC, 480 AC, 6 DC, 12 DC, 24 DC, 120 DC, 240 DC
Max Differential / Max Operating Pressure
Vacuum to 150 PSIG
Operating Environment
Corrosive, Hazardous, Indoor, Outdoor
Standards / Regulations
ATEX Zone 1-21, ATEX Zone 2-22, Class I Div 1, Class II Div 1, SIL, Type 1, Type 2, Type 3, Type 3S, Type 4, Type 4X, Type 6, Type 6P, Type 7, Type 9
-60°C to 80°C


  • Available in two versions, mounted directly to actuators with NAMUR interface per VDI/VDE 3845 or threaded to mount on the pipe
  • Valve body in Aluminum, Brass, or Stainless steel 316L
  • Exhaust ports are pipeable, providing better protection against harsh environments
  • DIN, watertight, and explosion-proof solenoids are available for use in mission-critical and hazardous areas
  • Low-power constructions are ideal for remote and alternative power locations
  • Integral breather block vents to spring side of the actuator to exhaust, preventing corrosion
  • Single- and dual-solenoid constructions are available that mount in any position
  • Global Ex approvals; ATEX, IEC EX, NEPSI, CUTR, KOSHA, UL, CSA, InMetro
  • All ports of NAMUR on the same side for a better water , DUST protection
  • Available will all Explosion proof solenoids: Ex d, Ex mb, Ex ia/Ib, Ex e mb, NEMA
  • Available in an arctic version, suitable for use in temperatures as low as -60°C
  • Compact spool valve convertible from 3/2 to 5/2 with a single flow plate design (551 Series only)


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