Normally Closed Direct Acting Solenoid Valve in Brass — 2/2 Way

Cematic's normally closed direct acting solenoid valve in brass is a 2/2-way direct-acting solenoid valve for ON/OFF control of fluids in small diameters — from 1/8" to 1/2" — in instrumentation systems, gas control, precision dosing, and low-flow industrial automation. Its direct action ensures reliable operation with differential pressure starting from 0.1 MPa and immediate response in milliseconds, without additional moving parts. Therefore, it is the standard choice for control points where the required flow does not justify a larger diameter solenoid and where response precision is a priority.

Unlike high-flow brass NC solenoids (3/4" to 2" diameters), this normally closed direct acting solenoid valve is optimized for 1/8", 1/4", 3/8", and 1/2" lines — standard diameters in industrial instrumentation, gas control, and process equipment where space and flow are limited.

Principle of Operation — Direct Acting NC Solenoid Valve

In the de-energized state (coil de-energized): the normally closed direct acting solenoid valve remains in the closed position — the spring holds the plunger on the seat, blocking fluid flow. When the coil is energized, the electromagnetic field directly lifts the plunger and opens the flow path. When de-energized, the spring automatically returns the plunger to the closed position.

Direct action is correct when:

• Differential pressure can be low — from 0.1 MPa (1 bar)
• The required diameter is 1/8" to 1/2" — a range where direct action is efficient without a pilot mechanism
• Automatic closure in case of electrical failure is the safe state of the process (NC)
• Immediate response and compact size are required at the installation point

Construction Materials

• Body: Brass — corrosion resistance for potable water, process water, compressed air, natural gas, LPG, and light hydraulic oils.
• Plunger: Stainless steel — corrosion-resistant and with optimized mass for fast direct-acting response.
• Seat Seal: NBR (Nitrile) — compatible with water, compressed air, natural gas, LPG, and mineral hydraulic oils within specified temperature ranges.
• Coil: Encapsulated, IP65 protection — suitable for humid environments and industrial dust.
• Connection: Female NPT thread — industrial standard in Mexico for instrumentation and fluid control in small diameters.

Technical Specifications

Normally Closed Direct Acting vs. High Flow Solenoid — Which to Choose?

Cematic offers two direct-acting NC solenoids in brass with NBR seals for different flow ranges. The normally closed direct acting solenoid valve in small diameters is correct when:

• The process line is 1/8" to 1/2" NPT
• The required flow is low — instrumentation, gas, precision dosing
• The inlet pressure exceeds 0.1 MPa (1 bar) at all times

For diameters from 3/4" to 2" with higher flows, the correct option is the high-flow brass NC solenoid →

Fluid Compatibility

• ✅ Potable water and process water — up to 1.0 MPa and 80 °C
• ✅ Compressed air — up to 1.0 MPa, -20 °C to 90 °C; pneumatic instrumentation
• ✅ Natural gas and LPG — verify local regulations and area classification before installation
• ✅ Mineral hydraulic oils — up to 1.0 MPa and 80 °C, compatible with NBR
• ✅ Non-corrosive industrial gases — nitrogen, dry CO₂, argon
• ⚠️ Pressure below 0.1 MPa: this direct-acting NC solenoid requires at least 1 bar of inlet pressure to operate correctly
• ⚠️ Temperature above 80 °C: the NBR seal degrades — use a solenoid with a Viton seal
• ❌ Concentrated acids, chlorinated solvents: use a solenoid with a stainless steel body

Applications of the Normally Closed Direct Acting Solenoid Valve

Gas control in industrial instrumentation
The normally closed direct acting solenoid valve in brass is the standard automatic shut-off component in 1/8" to 1/4" NPT gas lines. Its NC configuration ensures that gas is automatically shut off in case of any electrical failure — the correct safety state for natural gas and LPG lines. Furthermore, the brass body is compatible with these gases at typical working pressures in instrumentation.

Precision dosing in process equipment
In reagent dosing equipment and liquid dispensers where precise ON/OFF control of small volumes is required, the 1/8" to 1/2" diameters of this normally closed solenoid valve allow direct integration of control into the line without additional reducers. Consequently, the immediate response of direct action ensures the temporal precision of each dosing cycle.

Pneumatic instrumentation and control systems
In pneumatic control cabinets and instrumentation panels where signal air circulates through 1/4" or 3/8" lines, this direct-acting NC solenoid controls compressed air flow with millisecond response. Therefore, it is the correct solution in pneumatic instrumentation systems where automatic shut-off of the air signal is required in case of electrical failure.

Refrigeration and HVAC in small diameter lines
In compact refrigeration systems and laboratory equipment where working diameters are 3/8" or 1/2", this normally closed direct-acting solenoid controls the flow of refrigerants with automatic safety shut-off. Likewise, direct action ensures correct operation even in low differential pressure conditions.

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

Data Sheet