Modern engineering infrastructure is impossible without precise dosing and rapid shut-off of flows of liquids and gases. If a few decades ago this work was performed manually using conventional valves, today the industry standard is full automation. Electromagnetic valves became the same universal tool that transformed bulky pipeline assemblies into compact and manageable modules.
As a manufacturer of pipeline valves, UKSPAR knows how critical it is to choose the right actuator. A mistake in the choice can mean downtime of the line, broken automation or, much worse, an emergency situation at the facility. Let's take a closer look at the physics of the processes, engineering nuances and real scenarios of operation of this equipment.
Where are solenoid valves used and what tasks do they solve?
The scope of application of solenoid valves is extremely wide. They are used to automatically open and close the flow of media in pipelines. Here are just a few examples:
- Heating systems and boiler rooms. Here, valves control the gas supply to burners, regulate the flow of coolant in the circuits, and ensure safety. For example, they instantly shut off the gas when the flame disappears or the pressure drops.
- Water supply and automatic watering. In lawn or greenhouse irrigation systems, a water solenoid valve automatically turns the water supply on and off based on a signal from a controller or timer.
- Pneumatic systems. Controlling pneumatic cylinders, tools and mechanisms in production is impossible without high-speed air valves.
- Technological processes. In the food, chemical, and pharmaceutical industries, valves dose ingredients and control the flow of aggressive media in closed systems.
- Safety systems. Valves are used in fire extinguishing systems, emergency shutdown of pipelines and other critical nodes where speed of response is a key factor.
The main task that this device solves is automation and remote control. It allows you to integrate flow control into a single control system (controller, relay, industrial computer), eliminating the need for a person to manually turn valves and ensuring accuracy and speed of response.
The principle of operation of a solenoid valve
Despite the variety of types, the operating principle of most solenoid valves is based on the same physical basis.
The design is based on a solenoid – an electric coil with a ferromagnetic core (plunger) inside. When voltage is applied to the coil, a magnetic field is created that pulls in the plunger. This mechanical movement directly or indirectly (through a membrane or spool) opens or closes a through hole in the valve body. When the voltage disappears, the spring returns the plunger to its original position.
Thus, the valve has two main states – «Open» and «Closed», and switching between them occurs in a fraction of a second. This provides high accuracy and speed, which is especially important in automated systems.
Main types of solenoid valves
Solenoid valves are classified by several key characteristics: rest position, operating principle, operating medium, and body material. Understanding these types is the basis for making the right choice.
Normally closed and normally open valves
A normally closed valve (denoted NC) keeps the passage closed when there is no voltage on the coil and opens only when current is applied. This is the most common type, as it complies with the safety logic - in the event of a power failure, the system automatically shuts off the medium supply, rather than leaving it in the flow.
A normally open (NO) valve works the opposite way. Without voltage, the passage is open, and the supply of current closes it. This type is used where a power failure should not interrupt the process. For example, when it is required that the flow continues to move in the absence of a control signal, and stopping occurs only on command.
Separately, it is worth mentioning bistable (position-locking valves). Their spool is switched by a short current pulse and remains in the new position without constant power supply to the coil. This saves energy in systems with infrequent switching.
Direct-acting and pilot-operated valves
This is the most important technical distinction that is often ignored by inexperienced installers.
The direct-acting valve works according to the classic scheme: a magnetic field lifts the spool, opening the hole. The main advantage is that it is able to work at zero pressure in the pipeline. This is an ideal solution for drainage lines, tanks where the liquid flows by gravity, or for vacuum systems. However, due to the limited force of the solenoid, the diameter of the through hole here usually does not exceed 15-25 mm.
In indirect (pilot) valves, the coil controls only a small auxiliary orifice, and the main spool or diaphragm moves under the action of the pressure difference of the medium itself. This allows the use of a low-power coil even on valves of large diameter. However, a minimum pressure drop in the pipeline is required - because at practically zero pressure the pilot valve may not open.
Solenoid valves by working medium
The properties of the substance transported by the pipeline directly affect the design of the valve. The chemical composition, viscosity, presence of mechanical impurities and aggressiveness of the environment require the use of special materials for both the body and internal seals.
Water valves
The most popular segment of the market. These are devices for drinking water supply, process water, sewage and irrigation systems. For clean water, membrane models with seals made of ethylene propylene diene rubber (EPDM) or nitrile rubber (NBR) are used. They are cheap, effective and durable.
When it comes to contaminated wastewater or technical water with impurities, special direct-acting actuators or designs with a forced guide rod are used, where the membrane is not clogged with small debris.
Gas valves
Gas valves are always a matter of increased safety. Conventional membrane models cannot be used here due to the risk of gas molecules migrating through elastomers. Gas valves use only metal seats or special molded seals made of Viton (FKM). And the actuator itself is often made direct-acting or combined.
A separate category is gas shut-off valves, which instantly shut off the fuel supply to the burner in the event of a power failure or a leak sensor tripping. They have mandatory certification according to European standards EN 161.
Valves for steam and aggressive media
Working with steam involves extreme temperatures and the risk of corrosion. Ordinary rubber or brass are not suitable for such conditions. Steam requires the use of high-quality stainless steel or special cast iron housings. Sealing materials must withstand temperatures above +180 degrees, so fluoroplastic (PTFE) or heat-resistant Viton are used here.
For chemically aggressive substances (acids, alkalis, petroleum products), stainless steel is selected that is resistant to chemical corrosion. The entire internal structure, including the spring and plunger, is isolated from direct contact with the aggressive flow or is made of special alloys to avoid metal destruction and loss of tightness.
Manufacturing materials
The body material determines how long the solenoid valve will last under specific operating conditions and what working medium it is able to pass without the risk of destruction:
- Brass is the golden mean for standard engineering networks. It can withstand pressure up to 16-25 bar, does not corrode in ordinary water and is resistant to mechanical stress. Most domestic and commercial systems are assembled on brass models.
- Stainless steel is necessary where there are aggressive environments, high temperatures, or strict sanitary standards. The food industry, pharmaceuticals - everywhere they use steel grades 304 or 316. They are expensive, but they guarantee work for decades.
- Cast iron is used where greater mechanical strength is required. These are industrial pipeline systems, large diameter pipelines. The cast iron body withstands water hammer better than brass, although the material itself is heavier and less resistant to aggressive environments without additional coating.
- Polymers (nylon, polypropylene, PVC) are used for chemically aggressive liquids. Plastic is also indispensable in reverse osmosis systems and swimming pools, where chlorine actively destroys non-ferrous metals.
Sealing material is a separate science:
- NBR (nitrile butadiene rubber) – for petroleum products and air.
- EPDM – for hot water and steam, works great with alkalis.
- FKM (Viton) – for high temperatures, chemicals and hydrocarbons.
- PTFE (Teflon) – for the most aggressive acids and solvents.
To achieve the optimal ratio of price and performance, materials can be combined.
Solenoid valve selection parameters
Selecting a solenoid valve is a complex decision, where no parameter can be determined separately from the others. Voltage, diameter, pressure and temperature form a single system of requirements.
Coil voltage: 12V, 24V, 220V
The solenoid valve coil is designed for a specific supply voltage. This parameter determines which control system the valve can be combined with without additional converters.
The 220V solenoid valve is connected directly to the mains voltage. This is the simplest option for autonomous household and semi-industrial systems without a separate controller.
A 24V valve is typical for industrial automation and systems controlled by controllers and relays - low voltage is safer during installation and maintenance.
The 12V valve is used mostly in compact household and mobile systems, in particular in battery-powered automatic irrigation, where low power consumption is important.
Connection diameter and thread type
The size range starts from 1/8 inch and ends with DN100 and larger pipelines.
For small diameters, threaded connections (internal or external BSP/NPT thread) are used. This is fast, convenient and does not require welding.
The flange is used on diameters from DN50, as well as in systems with high pressure and vibrations. The flange connection guarantees tightness and allows easy dismantling of the valve for maintenance.
Working pressure and temperature
Each model has a nominal pressure range (PN). If you put a diaphragm valve rated for 10 bar in a line with 16 bar, it will either fail or fail to open due to excessive force on the seat.
The temperature range is limited by the seal material. Ordinary rubber works up to 80-90 degrees, Viton up to 150, Teflon up to 180. Exceeding the temperature leads to irreversible deformation of the membrane and loss of tightness.
Engineers also pay attention to the flow coefficient Kv. This parameter shows how much water at a temperature of 5-30 degrees will pass through a fully open valve in one hour with a pressure drop of 1 bar. Knowing the required flow rate of your system and the operating pressure, you can accurately calculate the required Kv.
Connectivity and automation
The main value of solenoid models lies in the possibility of their full integration into modern digital and analog control systems. This turns a conventional shut-off valve into an executive body of a smart home or automated industrial line.
Integration with controllers and relays
To build an automatic control system, the solenoid valve is connected to a control device. This can be a programmable logic controller (PLC), an electronic time relay, or a thermostat.
The control circuit works on a simple principle:
- the sensor records a change in a parameter (for example, an increase in temperature);
- transmits a signal to the controller;
- The controller closes the relay, supplying the required voltage to the armature coil.
Thanks to such integration, it is possible to implement complex operating algorithms. For example, in wastewater treatment plants. Where the controller can alternately open different lines for washing filters according to a clear schedule.
Application in boiler rooms and automatic irrigation systems
In boiler rooms, solenoid valves control:
- by supplying gas to the burner;
- cutting off heating circuits;
- emergency closure of highways following a signal from security systems.
Normally closed valves prevail here, which guarantee the shut-off of the supply in the event of a power failure.
In automatic irrigation systems, valves controlled by an irrigation controller open and close individual irrigation areas according to a set schedule. This automates the entire cycle without human intervention.
Typical faults and maintenance
The most common cause of valve failure is contamination of the working medium. Particles of scale, rust or mechanical impurities get between the spool and the seat, preventing complete closing or opening. This manifests itself as leakage in the closed state or incomplete opening of the flow. A filter in front of the valve reduces the risk of such a malfunction.
The second common problem is coil failure due to overvoltage, short circuit of the turns, or overheating during prolonged continuous operation beyond the rated life. A failed coil must be replaced, not repaired.
The third group of faults is mechanical wear of the membrane or seals. Loss of elasticity of rubber parts due to temperature, aggressive environment or time leads to leakage in the closed position.
Preventive maintenance consists of regularly checking the tightness of connections, cleaning the mesh filters in front of the device, and visually inspecting the electrical contacts for oxidation. Such actions allow you to detect worn parts before an emergency occurs.
How to choose a reliable solenoid valve
Considering the above, the selection process can be reduced to the following steps:
- Determine the working medium: water, gas, air, steam, aggressive liquid or petroleum product? The material of the housing and seals depends on this.
- Determine the function you need – do you need a normally closed or normally open valve? What type of action (direct, pilot) is right for your pressure?
- Select the parameters – match the connection diameter, operating pressure, and medium temperature with the technical specifications of the model.
- Choose the supply voltage – 220V, 24V or 12V depending on your existing system.
By following these recommendations, you will be able to choose a solenoid valve that will provide reliable and durable flow control in your system. The wide range presented in the UKSPAR catalog allows you to buy a solenoid valve for any task - from simple automatic watering to complex industrial automation systems.
