How to Choose a Solenoid Valve?

Selecting the correct solenoid valve is the backbone of a stable automated fluid control system. A single mismatched parameter can lead to coil burnout, leakage, or system failure. Based on ATO industrial experience, this guide outlines the core criteria for professional selection.

Medium characteristics

The first step isn't checking the pressure—it's analyzing what is flowing through the valve.

Corrosive Media:

1. Strong Corrosion: You must use an isolated diaphragm structure to ensure the media is completely separated from the plunger and internal metal parts. Material choices should be plastic (UPVC/CPVC) or high-grade Stainless Steel.
2. Neutral Media: Even for water or air, Copper Alloy or Stainless Steel is recommended. Common cast iron bodies are prone to rust flakes that can break off and jam the valve.
3. Critical Warning: For ammonia-based media, Copper valves are strictly prohibited due to chemical reactions; Stainless Steel or special alloys must be used.

Viscosity & Cleanliness:

1. Viscosity: Media viscosity should typically be < 50cSt. If it exceeds this, use a multi-functional valve for diameters > 15mm, or a specialized high-viscosity valve for smaller diameters.
2. Cleanliness: If the media is not pure, a strainer/filter must be installed upstream. Under low-pressure conditions, direct-acting diaphragm valves offer better tolerance for impurities.

Flow Direction:

If the media requires directional circulation and zero backflow, choose a valve with a check function or a bidirectional design.

Environmental conditions

The environment determines the protection rating required for the coil and housing.

1. Explosive & Harsh Environments: In hazardous areas, you must strictly match the Explosion-proof rating (e.g., Explosion proof solenoid valve). For outdoor or dusty sites, a waterproof and dustproof rating (IP65/IP67) is mandatory.
2. Temperature Extremes: Both ambient and media temperatures must stay within the valve's rated range to prevent coil failure or seal aging.
3. Mechanical Stress: For environments with vibration, collision, or shock (e.g., marine or mobile equipment), prioritize Anti-vibration specialized solenoid valves.

Pipeline parameters

The physical integration of the valve into your pipeline determines both the safety threshold and the fluid dynamics of the entire system.

Rated Pressure:

The nominal pressure of the valve must exceed the maximum working pressure of the pipeline to ensure a safety margin.

Working Differential Pressure:

1. Indirect/Pilot Operated: Relies on the media's own pressure to open. Requires a minimum differential pressure (usually > 0.04MPa).
2. Direct-Acting / Distributed Direct-Acting: These can operate even at zero differential pressure (e.g., vacuum or gravity flow systems).

Diameter Matching:

Select the nominal diameter based on flow requirements. Generally, the valve port should match the pipeline's internal diameter to avoid water hammer effects caused by sudden flow velocity changes.

Power conditions

AC Power: High starting force and fast opening. Voltage fluctuations should be kept within +%10%.-15%.

DC Power: Smoother operation with a tolerance of ±%10. If fluctuations exceed this, voltage stabilization is required.

The rated current and power consumption should be selected according to the power supply capacity. It should be noted that the VA value is high during AC starting, and the indirect pilot solenoid valve should be preferred when the capacity is insufficient.

Reliability

Work system: For the case where the valve is opened for a long time and only closed for a short time, a normally open solenoid valve should be used.

Operating frequency: When the operating frequency is required to be high, the structure should be preferably a direct-acting solenoid valve, and the power supply is preferably AC.

Frequently Asked Questions

Q1. How do I choose the right seal material (NBR, Viton, EPDM)?

A: The seal material is the "longevity gene" of a solenoid valve. Based on different working conditions, ATO provides the following recommendations:

For General Water, Gas, or Oil (Temperature < 80°C):

Recommended Material: NBR— The "King of Value" in the industrial world.

ATO Recommended Series: Solenoid Valve, 2 Way, Normally Closed, 12V/24V/220V for air water oil. Ideally suited for irrigation, air compressor drainage, and general fluid control with maximum cost-efficiency.

For High-Temperature Water or Steam (Temperature < 120°C):

Recommended Material: EPDM— The expert in heat-aging resistance.

ATO Recommended Series: Solenoid Valve, 2 Way, Normally Closed, 24V/220V for steam water air. Designed specifically for boiler systems and sterilization equipment, it effectively prevents the seal from hardening during continuous thermal cycling.

For Harsh Chemicals, Acids/Alkalis, or High-Heat Environments (Up to 150°C):

Recommended Material: Viton— The "Body Armor" for extreme conditions.

Widely utilized in chemical dosing, fuel refining, and high-precision laboratory fluid control.

Consequence of Failure: Material mismatch leads to seals swelling, deforming, or disintegrating within days, resulting in severe internal or external leakage.

Q2. Should I choose a "Normally Open" or "Normally Closed" valve?

A: This depends on the valve's state during the majority of its operation, which directly impacts coil longevity.

• Normally Closed (NC): Best for "Short-term Open" scenarios (e.g., automatic flushing, quantitative filling), where the valve stays shut most of the time.
• Normally Open (NO): Best for "Long-term Open" scenarios (e.g., cooling circulation, safety exhaust), where the valve needs to stay open and only closes at specific moments.

Pro Tip: Avoid keeping a Normally Closed valve energized for more than 8 consecutive hours a day, or the coil may overheat and burn out.

Q3: Why shouldn't I just buy a valve with a larger diameter to be safe?

A: Many believe that "bigger is better," but this is a common misconception in fluid control.

A diameter that is too large can lead to unstable plunger stroke control, causing oscillations.

ATO.com provides pneumatic solenoid valves and general solenoid valves for you. These solenoid valves are available in brass, aluminum, and stainless steel and various port sizes for selection. Buy now!