Thread Content
Guide to Solenoid Valve Selection I. Overview of Solenoid Valves Tracing the history of solenoid valves, to date they can be divided into three main categories based on their principle of operation, both domestically and internationally (namely: direct-acting, step-by-step direct-acting, and pilot-operated). Furthermore, due to differences in valve disc structure and materials as well as variations in operating principles, they are further divided into six subcategories (direct-acting diaphragm structure, step-by-step diaphragm structure, pilot-operated diaphragm structure, direct-acting piston structure, step-by-step piston structure, and pilot-operated piston structure). 1. Direct-acting solenoid valve Principle: When electricity is applied, the electromagnetic coil generates an electromagnetic force that lifts the closing element away from the valve seat, thereby opening the valve ； When the power is cut off, the electromagnetic force disappears, and the spring force presses the closing element against the valve seat, causing the valve to close. Features: It can operate normally under vacuum, negative pressure, and zero pressure, but the typical diameter does not exceed 25 mm. 2. Step-type direct-acting solenoid valve Principle: It operates on a combination of direct-acting and pilot-operated mechanisms; when the pressure difference between the inlet and outlet is ≤0.05 Mpa, upon power application, the electromagnetic force lifts the pilot valve and the main valve’s closing element upward sequentially, thereby opening the valve. When the pressure difference between the inlet and outlet is >0.05 Mpa and power is applied, the electromagnetic force first opens the pilot valve; as a result, the pressure in the lower chamber of the main valve increases while the pressure in the upper chamber decreases, and this pressure difference is used to push the main valve upward ； During a power outage, the pilot valve and the main valve use spring force or medium pressure to push the closing element downward, thereby closing the valve. Features: It can operate reliably at zero pressure difference or in vacuum as well as under high pressure, but it requires a large power supply and must be installed vertically. 3. Pilot-operated solenoid valve Principle: When electric current is applied, electromagnetic force opens the pilot hole, causing the pressure in the upper chamber to drop rapidly. This creates a pressure difference with higher pressure below and lower pressure above the closing element, pushing it upward and thus opening the valve ； When power is lost, the spring force closes the pilot hole; the inlet pressure enters the upper chamber rapidly through the bypass hole, creating a pressure difference with lower pressure below and higher pressure above the valve closing element, which pushes the closing element downward to close the valve. Feature: The upper limit of the fluid pressure range is very high, but the fluid pressure difference condition must be satisfied. http://www.fspv.com/imge/dian1.jpg Schematic diagram of direct-acting type; http://www.fspv.com/imge/dian2.jpg Schematic diagram of distributed direct-acting type; http://www.fspv.com/imge/dian3.jpg Schematic diagram of pilot-operated type. II. Four key principles for selecting solenoid valves – safety, reliability, suitability, and cost-effectiveness. 1. Safety: Neglecting safety can lead to disasters! 1. Corrosive media: Plastic King solenoid valves and all-stainless steel options are recommended ； For highly corrosive media, an isolated diaphragm type must be used. In neutral media, solenoid valves with copper alloy as the valve body material are also a good choice; otherwise, rust particles often fall off from the valve body, especially in situations where the valve is not used frequently. Copper materials cannot be used for ammonia valves. 2. Explosive environments: Products with the appropriate explosion-proof rating must be selected; waterproof and dust-proof models should be used for outdoor installations or locations with high dust levels. 3. The nominal pressure of the solenoid valve should exceed the highest operating pressure in the pipeline. 2. Applicability: Not applicable means spending money on something useless, plus it causes extra trouble! 1. Medium properties: 1.1 Different types of solenoid valves should be used for gaseous, liquid, or mixed states; for example, ZQDF is used for air, ZQDF—Y for liquids, and ZQDF—2 (or -3) for steam – otherwise, misoperation may occur. The ZDF series of multi-functional solenoid valves can be used with both gas and liquids. It is best to specify the medium condition at the time of ordering, so that the installation user does not need to adjust it again. 1.2 Products of different specifications for medium temperatures; otherwise, the coil will burn out and the seals will age, severely affecting their lifespan. 1.3 Dielectric viscosity, usually below 50 cSt. If this value is exceeded, and the bore diameter is greater than 15 mm, a ZDF series multi-functional solenoid valve must be ordered as a special order. Solenoid valves with a bore diameter of less than 15 mm for high viscosity fluids. 1.4 When the cleanliness of the medium is not high, a backflow filter valve should be installed in front of the solenoid valve; when the pressure is low, a direct-acting diaphragm solenoid valve can be used. 1.5 If the 1.5 medium flows in a directional manner and backflow is not allowed, ZDF—N and ZQDF—N require bidirectional flow only; special requests should be made in such cases. 1.6 The medium temperature should be within the range permitted by the solenoid valve. 2. Pipeline parameters 2.1 Select the valve diameter and model based on the requirements of the medium flow direction and the pipeline connection method. 2.2 The nominal diameter is selected based on the flow rate and the Kv value of the valve; it can also be chosen to match the inner diameter of the pipeline. 2.3 Operating pressure difference: An indirect pilot type can be used when the minimum operating pressure difference is above 0.04 Mpa ； Those with a minimum operating pressure difference close to or less than zero must use direct-acting or step-direct-acting types. 3. Environmental Conditions 3.1 The maximum and minimum temperatures of the environment should be within the allowable range; if they exceed this range, a special order must be placed. 3.2 In environments with high relative humidity or exposure to water droplets and rain, waterproof solenoid valves should be used. 3.3 In environments subject to frequent vibration, shock, and impacts, special types of solenoid valves, such as those designed for use on ships, should be chosen. 3.4 In corrosive or explosive environments, it is preferable to choose models resistant to corrosion based on safety requirements. 3.5 If space is limited, multi-functional solenoid valves should be used, as they eliminate the need for bypass circuits and three manual valves, and facilitate online maintenance. 4. Power supply conditions 4.1 Depending on the type of power supply, AC and DC solenoid valves are selected accordingly. Generally, AC power is easy to obtain. 4.2 For voltage specifications, AC220V and DC24V should be given priority whenever possible. 4.3 For power supply voltage fluctuations, +%10% to -15% is typically allowed for AC, while ±10% is acceptable for DC. If these limits are exceeded, voltage stabilization measures must be taken or special ordering requirements should be specified. 4.4 The rated current and power consumption should be selected based on the power supply capacity. It should be noted that the VA value is high during start-up under communication conditions; indirect-acting solenoid valves should be given priority when capacity is insufficient. 5. Control accuracy 5.1 Ordinary solenoid valves have only two positions: on and off. When high control accuracy and stable parameters are required, please choose multi-position solenoid valves ； The Z3CF three-position normally open solenoid valve offers three flow states: slightly open, fully open, and closed ； The ZDF—Z1/1 combined multi-functional solenoid valve has four flow rates: full open, wide open, narrow open, and full open. 5.2 Action time: Refers to the time from when the electrical signal is applied or removed until the main valve completes its action. Only our company’s patented multi-functional solenoid valves allow for separate adjustment of the opening and closing times, which not only meets the requirements for control precision but also prevents damage caused by water hammer. 5.3 Leakage rate: The leakage rate value given for the sample corresponds to the standard economic grade; if it seems too high, please place a special order. 3. Reliability: Unreliability will damage the entire system! 1. Service life: This item is not included in the factory testing procedures and falls under the category of type testing. To ensure quality, brand-name products from reputable manufacturers should be chosen. 2. Working system: There are three types, namely long-term working system, repeated short-term working system, and short-term working system. For situations where the valve remains open for a long time with only short periods of closure, an normally open solenoid valve is recommended. When used in a short working schedule with large batch sizes, it can be ordered specially to reduce power consumption. 3. Operating frequency: When a high frequency of operation is required, a direct-acting solenoid valve is the preferred choice for the structure, and alternating current is the preferred power supply. 4. Operational reliability: Strictly speaking, this test has not yet been officially included in China’s professional standards for solenoid valves; to ensure quality, it is necessary to choose branded products from reputable manufacturers. In some situations, the number of actions required is not high, but the demand for reliability is extremely high, such as in firefighting and emergency protection – these areas must not be taken lightly. It is particularly important to also use two safeguards in combination. 4. Cost-effectiveness: Being uneconomical means a waste of funds, effort, and even lives. It is one of the criteria considered, but cost-effectiveness must be achieved on the basis of safety, suitability, and reliability. Economics is not just about the price of a product; its functionality and quality, as well as the costs associated with installation, maintenance, and other accessories, should be given priority. More importantly, the cost of a solenoid valve in the entire automatic control system, and even within the production line, is minimal; choosing the wrong one in an attempt to save money can result in significant damage. In short, cost-effectiveness refers not only to the price of a product, but also to its performance-to-price ratio as well as its overall cost-to-price ratio. III. Pay attention to six aspects of on-site operating conditions (i.e., select based on pipeline parameters, fluid parameters, pressure parameters, electrical parameters, operation mode, and special requirements). Selection criteria: 1. The solenoid valve is selected based on pipeline parameters: diameter specification (i.e., DN) and connection type. 1. The diameter (DN) is determined according to the inner diameter of the pipes in place or the required flow rate. 2. For the interface type, flange interfaces are generally required for DN50 and above, while for DN50 and below, the choice can be made according to the user’s requirements. 2. Select the solenoid valve based on fluid parameters: material, temperature range. 1. For corrosive fluids: it is advisable to use corrosion-resistant solenoid valves made of all stainless steel ； For use with ultra-pure fluids: it is advisable to choose solenoid valves made of food-grade stainless steel. 2. High-temperature fluids: Electromagnetic valves made from high-temperature resistant electrical and sealing materials should be selected, and those with a piston-type structure are preferred. 3. Fluid state: It can be gaseous, liquid, or in a mixed state; in particular, when placing orders for pipes with a diameter larger than DN25, it is essential to distinguish between these states. 4. Fluid viscosity: It can generally be chosen arbitrarily as long as it is below 50 cSt; if it exceeds this value, a high-viscosity solenoid valve should be used. 3. Selection of solenoid valves based on pressure parameters: principles and structural types. 1. Nominal pressure: This parameter has the same meaning as that of other standard valves; it is determined according to the nominal pressure of the pipeline. 2. Work pressure: If the work pressure is low, a direct-acting or step-direct-acting principle must be selected ； When the minimum operating pressure difference is above 0.04 Mpa, direct-acting, step-direct-acting, and pilot-operated types can all be used. 4. Electrical selection: For voltage specifications, AC220V and DC24 are preferable as they are more convenient to use. 5. Choose based on the duration of continuous operation: normally closed, normally open, or capable of remaining powered on continuously. 1. When the solenoid valve needs to remain open for an extended period of time, with that time being longer than the time it is closed, a normally open type should be selected. 2. If the operation time is short or the on and off periods are brief, choose the normally closed type. 3. However, for some applications related to safety protection, such as flame monitoring in furnaces and kilns, normally open types cannot be used; instead, types that can remain powered on continuously should be chosen. 6. Select auxiliary functions based on environmental requirements: explosion-proof, check valve, manual, fog-proof, water spray-proof, submersible. 1. In explosive environments: solenoid valves with the appropriate explosion-proof rating must be used (available in our company: dII BT4, dII CT5, Ex m I/II T4). 2. When there is backflow of fluid in the pipeline, our company’s OK71-N and OK72-N series solenoid valves with check function can be selected. 3. When manual operation of the solenoid valve is required on-site, our company’s solenoid valves with manual function can be selected. 4. In areas with outdoor installation or high dust levels, waterproof and dust-proof models (with a protection rating of IP54 or higher) should be selected. 5. Submersible solenoid valves (with a protection rating of IP68 or higher) must be used for fountains. IV. Ordering Instructions 1. When placing an order, please specify the model, nominal diameter, nominal pressure, working medium, operating pressure difference, medium temperature, power supply voltage, and medium viscosity. 2. The voltage required for the solenoid valve to operate properly is 220V; if this value is exceeded, please specify the allowable voltage variation when placing the order. Power supply voltages for other specifications are available upon special order. 3. If the valve is kept open for 12 hours or under continuous power supply, please indicate this. Of course, since the surrounding environment contains flammable and explosive materials, please use an explosion-proof solenoid valve