Normally Closed Brass Solenoid Valve — Direct Acting, High Flow

Cematic's normally closed brass solenoid valve is the standard ON/OFF control component for industrial systems where the fail-safe condition in the event of an electrical failure is fluid shut-off. Unlike NO (normally open) solenoids, this solenoid valve keeps the flow blocked while the coil is de-energized and opens it when an electrical signal is received. Therefore, it is the most common configuration in industrial automation: fluid flows only when there is an active command from the controller.

Its direct-acting, high-flow design allows it to handle significant flow rates in 3/4" to 2" diameters without relying on the system's differential pressure to operate — consequently, it works correctly even with zero differential pressure, unlike pilot-operated solenoids that require a minimum upstream pressure to open.

Operating Principle — Normally Closed (NC)

In the de-energized state (coil de-energized): the valve remains closed — the internal spring keeps the plunger on the seat, blocking fluid flow. When the coil is energized, the electromagnetic field lifts the plunger and opens the flow. When de-energized, the spring automatically returns the plunger to its closed position.

This configuration is correct when:

• The fluid must be cut off in case of a power failure (safe state = closed)
• The valve remains closed most of the time and opens by a signal from the controller
• Automatic closing is required in dosing systems, zone irrigation, or process control
• Process safety requires that flow be interrupted in the event of any unscheduled power outage

For applications where flow must continue in the event of an electrical failure, the correct option is the normally open (NO) brass solenoid valve →

Construction Materials

• Body: Zinc-plated brass — corrosion resistance for potable water, process water, compressed air, dry industrial gases, and light hydraulic oils. A cost-effective solution for most general industrial applications.
• Plunger: Stainless steel with optimized mass for reliable spring-return closing and rapid electromagnetic opening.
• Seat Seal: NBR (Nitrile) — compatible with water, compressed air, and mineral hydraulic oils up to 80 °C. For aggressive fluids or higher temperatures, check compatibility with Cematic's technical team.
• Coil: Resin encapsulated, IP65 protection — suitable for humid environments, with splashes and industrial dust.
• Connection: Female NPT thread — industrial standard in Mexico, compatible with steel, copper, and PVC pipes with adapters.

Technical Specifications

Voltage Selection

• 24 VDC: Standard in industrial control cabinets with PLC and DC power supply. Safety voltage, the most common option in new installations and modern automated systems. Available in 2" diameters.
• 110 VAC: For installations with 110 V single-phase circuits available in the field — the most widespread voltage in industry in Mexico and the United States. Available in all diameters.
• 220 VAC: For power panels with bi-phase distribution. Available in all diameters.

Fluid Compatibility

• ✅ Potable water and process water — up to 0.7 MPa (7 bar) and 80 °C
• ✅ Compressed air — up to 1.0 MPa (10 bar), industrial pneumatic service
• ✅ Mineral hydraulic oils — up to 0.7 MPa, compatible with NBR seal
• ✅ Non-corrosive industrial gases — nitrogen, dry CO₂, industrial air
• ⚠️ Fluids with suspended particles: install an upstream in-line filter to protect the seal and orifice
• ⚠️ Temperature above 80 °C: the NBR seal loses properties — use the SS304 solenoid with Viton seal →
• ❌ Concentrated acids, chlorinated solvents, seawater: use a solenoid with stainless steel body and Viton seal

NC vs NO — which to choose?

The selection between normally closed and normally open defines the system's behavior in the event of an electrical failure. Therefore, it is one of the most important decisions when specifying a solenoid valve:

• Normally Closed (this product): Fluid is automatically cut off in the event of an electrical failure. This is the standard configuration in dosing systems, zone irrigation, process control, and any application where uncontrolled flow represents an operational or safety risk.
• Normally Open (NO): Fluid continues to flow in the event of an electrical failure. This is the correct configuration in refrigeration, cooling, and heating systems where interrupting flow due to a power outage would cause damage to the protected equipment.

Main Industrial Applications

Technified irrigation and zone control
In drip and sprinkler irrigation systems, the normally closed solenoid valve is the standard configuration: water flows only during the programmed irrigation cycle and is automatically cut off at the end or in case of any electrical failure, preventing floods or water waste. Therefore, it is the most used zone control component in automated agricultural and industrial irrigation.

Dosing and industrial process control
In manufacturing plants, packaging lines, and reagent dosing systems, this NC solenoid valve ensures that fluid only circulates when there is an active signal from the PLC or controller. In addition, automatic closing in the event of an electrical failure protects the process from spills or uncontrolled contamination.

Industrial washing and cleaning systems
In wash tunnels, parts washers, and CIP equipment, the NC solenoid controls the supply of water and cleaning solutions by zones and programmed times, with automatic closing at the end of each cycle. Consequently, it reduces water and cleaning agent consumption compared to manual systems.

Flow control in machine tools
In machining centers and CNC lathes, this solenoid valve controls the supply of cutting fluid during machining. NC closing ensures that the coolant is automatically cut off when the machine is turned off or in the event of an electrical failure, without the need for manual intervention.

Dispensers and automatic process equipment
In liquid dispensers, automatic mixers, and batch process equipment, the NC configuration allows fluid control to be integrated directly from the PLC with immediate response, ensuring that no fluid circulates outside the programmed process cycle.

For the complete range of solenoid valves, see solenoid valve collection →

Technical Data Sheet