Normally Closed Direct Acting Stainless Steel Solenoid Valve — SS304, Viton

Cematic's normally closed direct acting stainless steel solenoid valve is a 2/2-way direct acting solenoid valve with an SS304 body and Viton seal for ON/OFF control of fluids in instrumentation diameters — 1/8" and 3/8" NPT — where brass is not compatible with the fluid or where greater chemical resistance of the seal is required. Its direct action operates from zero pressure (0 bar), without the need for minimum differential pressure, making it suitable for systems that start without pressure or operate with variable pressure. In addition, its automatic closure upon electrical failure (NC) makes it the standard safety option for controlling aggressive fluids in instrumentation and process applications.

Unlike the direct acting NC brass solenoid with NBR seal, this normally closed direct acting stainless steel solenoid valve incorporates a Viton (FKM) seal — compatible with a significantly wider chemical range than NBR, including synthetic oils, organic solvents, and aggressive process fluids — and an SS304 body without metal ion contribution to the fluid.

Operating Principle — Normally Closed (NC) Direct Acting Solenoid

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

The key advantage of direct acting over pilot operated is that it operates from zero differential pressure — the system can start without pressure, and the valve functions correctly at all times, regardless of line pressure. Therefore, it is the correct choice for systems with variable pressure or cold starts.

SS304 + Viton vs. Brass + NBR — Why it Matters in Instrumentation Diameters

In small instrumentation diameters, material selection is not always obvious. The following describes cases where this direct acting NC solenoid in SS304 is the correct choice compared to the brass version:

• Fluid Chemical Compatibility: Viton resists synthetic oils, some organic solvents, fuels, and aggressive fluids that would degrade NBR. Likewise, SS304 resists fluids that attack brass — such as slightly acidic solutions or fluids that should not be contaminated with copper or zinc ions.
• Fluid Purity: SS304 does not contribute metal ions to the fluid — a requirement in purified water, laboratory, pharma, and food processing applications where metallic contamination is unacceptable.
• Material Specification: In plants where the process piping class specifies stainless steel for all fluid-contacting components, this solenoid allows compliance with the specification at instrumentation points without exception.
• Pressure from Zero: Both direct acting versions (brass and SS304) operate from 0 bar. However, the SS304 version covers fluids that the brass version cannot handle.

Construction Materials

• Body: Stainless steel 304 (SS304) — corrosion resistance for process water, aqueous solutions, moderately aggressive industrial fluids, and applications where purity of the fluid-contacting material is a requirement.
• Plunger: Stainless steel — resistant to corrosion by the process fluid.
• Seat Seal: Viton (FKM) — compatible with synthetic oils, fuels, non-halogenated organic solvents, and aggressive process fluids that would degrade NBR. Operating temperature up to 80 °C in water and oil, up to 90 °C in air.
• 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

Fluid Compatibility — Normally Closed Direct Acting Stainless Steel Solenoid Valve

• ✅ Purified water and demineralized water — no metal ion contribution from SS304
• ✅ Process water and potable water — up to 0.7 MPa and 80 °C
• ✅ Compressed air — up to 0.7 MPa, -20 °C to 90 °C; pneumatic instrumentation
• ✅ Synthetic and mineral oils — Viton compatible with a wider range than NBR; up to 80 °C
• ✅ Non-halogenated organic solvents — verify specific compatibility with Cematic technical team
• ✅ Non-corrosive industrial gases — nitrogen, dry CO₂, argon
• ⚠️ Fluids with suspended solids: install an upstream inline filter to protect the seal and orifice
• ⚠️ Temperature above 80 °C in water or oil: check for availability of a version with a wider temperature range with Cematic technical team
• ❌ Concentrated acids, halogenated solvents, fluids with high chlorides: SS304 may be insufficient — consult for SS316 requirement

Applications of the Normally Closed Direct Acting Stainless Steel Solenoid Valve

Instrumentation and control of aggressive fluids in small diameters
The normally closed direct acting stainless steel solenoid valve is the correct choice at instrumentation points where the process fluid excludes brass due to chemical compatibility or purity requirements. In chemical, pharmaceutical, and food plants, 1/8" and 3/8" measurement, sampling, and control points must meet the same material specification as the rest of the line. Therefore, this SS304 + Viton solenoid is the logical continuation of the process piping class to the instrumentation components.

Purified water and laboratory
In laboratory equipment, reverse osmosis plants, and purified water systems where any metallic contribution to the fluid is unacceptable, this direct acting NC stainless steel solenoid valve controls water flow with automatic closure upon electrical failure. In addition, direct action from zero bar ensures correct operation in low-pressure systems typical of laboratory and water treatment plants.

Dosing of chemically aggressive fluids
In dosing systems for reagents, diluted acidic solutions, organic solvents, and other fluids incompatible with NBR or brass, the Viton seal of this direct acting NC solenoid guarantees the integrity of the seal in continuous contact with the process fluid. Consequently, it reduces premature seal failures and maintenance costs compared to solenoids with NBR seals under the same chemical conditions.

Pneumatic systems and air control in aggressive environments
In installations where the environment is corrosive or where compressed air contains traces of moisture and contaminants, the SS304 body of this normally closed direct acting solenoid offers greater durability than galvanized brass in prolonged exposure. Likewise, it operates correctly from -20 °C to 90 °C in air, covering industrial environments with significant thermal variations.

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Technical Data Sheet