Faced with the wide variety of solenoid valves available on the market, many people find themselves in a dilemma when it comes to choosing the right model: What is the difference between direct-acting and pilot-operated types? How should one choose between normally open and normally closed models? Can solenoid valves for water, gas, and oil be interchanged? In fact, there is no unified standard for the classification of solenoid valves. The most commonly used classification method is based on working principle, structural form, medium type, and on-off state. Each classification corresponds to a specific usage scenario. By clarifying the classification logic, one can achieve twice the results with half the effort when selecting the right model.
Classification based on working principle is the most core classification method, mainly divided into three major categories: direct-acting, pilot-operated, and step-direct-acting. This is also the primary reference for model selection. The direct-acting solenoid valve is the most basic type, relying on electromagnetic force to directly drive the valve core to open and close, without the assistance of medium pressure. It can be opened normally at zero pressure and has extremely fast response speed, suitable for low-pressure and low-flow scenarios such as household water control and small pneumatic systems. However, its disadvantage is that the diameter is small, unable to meet high-flow demands. The pilot-operated solenoid valve relies on the medium's own pressure to push the valve core, requiring a certain pressure difference of the medium to start. It has a large diameter and high flow rate, suitable for high-pressure and high-flow industrial scenarios such as urban water supply and chemical pipelines. However, it cannot be opened at zero pressure, limiting its application scenarios. The step-direct-acting type combines the advantages of both, capable of starting at zero pressure and adapting to high flow rates. It is a general-purpose solenoid valve with a slightly higher price and a wider range of application scenarios.
Based on the on-off state, solenoid valves are categorized into three types: normally open, normally closed, and self-holding. These types directly determine the valve's de-energized state. The normally closed solenoid valve is the most common type. When de-energized, the valve is closed, and when energized, it is open. It is suitable for most conventional scenarios, such as daily water control and gas supply, with low energy consumption. The normally open type is the opposite. When de-energized, the valve is open, and when energized, it is closed. It is commonly used in scenarios requiring long-term flow and emergency shutdown, such as fire water supply and emergency exhaust. The self-holding solenoid valve has a memory function. It switches states once when energized and maintains its original state after de-energization, eliminating the need for continuous energization and resulting in extremely low energy consumption. It is suitable for pipeline control that does not require switching for extended periods, such as remote water pipelines.
Divided by medium type, there are mainly water solenoid valves, gas solenoid valves, oil solenoid valves, fuel gas solenoid valves, corrosion-resistant solenoid valves, etc. The core difference lies in the valve body material and sealing components. Water solenoid valves often use brass or stainless steel valve bodies and rubber seals, suitable for clear water, sewage, and other aqueous media; gas solenoid valves focus on sealing and explosion resistance, suitable for compressed air, nitrogen, and other gases; oil solenoid valves require oil corrosion resistance, with valve bodies and sealing components made of oil-resistant materials; fuel gas and chemical medium solenoid valves require explosion resistance and corrosion resistance to eliminate leakage risks. Remember: solenoid valves for different media must not be interchanged, otherwise issues such as leakage, corrosion, and valve jamming may occur.
In addition, according to structural forms, it can be divided into straight-through type, right-angle type, flange type, and threaded type; according to explosion-proof grade, it can be divided into ordinary type and explosion-proof type, suitable for flammable and explosive scenarios; according to voltage, it can be divided into AC 220V, DC 24V, 12V, etc. In industrial scenarios, DC 24V is commonly used for higher safety. When selecting a model, one should not only consider a single classification, but also make a comprehensive judgment based on medium type, pressure, flow rate, installation space, and control requirements. For example, for household water purifiers with low pressure water control, a direct-acting, normally closed, water solenoid valve should be selected; for industrial high-flow high-pressure pipelines, a pilot-operated, flange-connected, stainless steel solenoid valve should be chosen; in flammable and explosive chemical scenarios, an explosion-proof corrosion-resistant solenoid valve must be selected.
Many novices only focus on price when selecting valve models, ignoring core parameters such as pressure, medium, and voltage, which can lead to valve malfunctions or even safety accidents. In fact, selecting solenoid valves is not complicated. By keeping in mind the principle of "medium determines material, pressure determines principle, scenario determines state, and demand determines specification", you can quickly identify the appropriate model, ensuring both effective use and extending the valve's service life.
