An Overview of Solenoid Valves
When fluids such as a gas or liquid have to be mixed or distributed from one point to another, a solenoid valve is often deployed. These valves come in varying types and designs and are used in different applications from heating systems to irrigation.
Below, we’ve discussed everything you need to know about solenoid valves, including the solenoid valve working principle, types, and buying guide.
What Is a Solenoid Valve and How Does It Work?
Solenoid valves are electromechanical devices used to control fluid flow in various settings. They are used to release, shut off, mix or dose liquid and gas media for different applications. By automating the closing and opening of valves, these devices make various industrial operations faster and efficient.
Solenoid valves use an electromagnetic coil to change the state of valve operation from open to close or close to open. A normally closed (NC) solenoid opens when an electric current energizes the coil. Here, the valve is lifted by an electromagnetic force (EMF) produced by the coil. For a normally open (NO) design, the solenoid closes when an electric current energizes the coil. They return back to their normal position via a mechanical spring. These switching mechanisms can be used independently or simultaneously depending on the desired use or application.
Valve Operation
Solenoids come with varying modes of actuation designed for different applications and use cases. To better understand the working principle of the electrically-operated valves, we’ll discuss the three mechanisms of valve operation. These are:
Direct-acting Valves
For direct-acting solenoid valves, the valve seat is attached to the plunger. For a normally closed solenoid valve, the plunger is down and the seat creates a seal around the orifice blocking any media flow. When energized, it lifts the plunger allowing flow. It is the opposite for a normally open solenoid valve.
Under this category, we’ve direct-acting 2-way valves and 3-way valves. Two-way valves come with one outlet and one inlet port. With the direct-acting 3-way valve, there are two valve seats and three port connections. One of the ports is always closed and two of them are always connected. They are used for distributing and mixing applications. Energizing the coil changes the open and closed ports.
Indirect-acting Valves
These are also called pilot-operated or servo-operated valves. They use the pressure difference between the downstream and upstream media to close and open. There is a diaphragm between the inlet and outlet ports. The plunger and seat operate similar to a direct-acting solenoid valve, but they control a small channel that allows the inlet media to the top of the diagram. Since the inlet media has a lower pressure than the outlet media (bottom of the diaphragm), the pressure difference opens the diagram allowing media to flow through. These types of valves are typically used if there is a sufficient pressure difference (0.5 bar) and a high enough flow rate.
Semi direct-acting Valves
Semi-direct acting solenoid valves are able to work from 0 bar, but can handle a higher flow rate than direct acting solenoid valves since they do use the pressure differential to its advantage. The plunger in this type is directly connected to the diaphragm, so the added force from the solenoid (or spring) allows it to operate even with no pressure differential (or assisted by it).
Choosing Solenoids for Different Applications
Now that you know the different solenoid valve types, the next is to understand the compatibility criteria for choosing them for varied applications. Without the right guidance and knowledge in this particular field, you can easily install an incompatible valve. Here are the factors to consider:
The Medium Type
Solenoid valves are made from different materials such as brass, plastic, steel, bronze, and aluminum. These materials come with varying chemical properties, e.g., heat and corrosion resistance. Depending on the media you want to regulate, you should look for compatible material. For instance, plastic can withstand several media but isn’t suitable for use with hot fluids.
For acidic or salty compounds, use corrosion-resistant steel or brass plated with nickel. And for oil or steam medium, use an oil-resistant and compatible steam solenoid.
Environmental Conditions
Always choose a solenoid valve based on the environmental conditions it will operate in. For instance, a solenoid valve used in an ATEX-required environment would differ from the one used for irrigation. Similarly, valves that operate indoors may be exposed to high temperatures or dusty conditions. In most environments, you should go for an IP-rated valve. This helps withstand any splashes that could damage or affect the efficiency of the solenoid.
In other words, you always want to think ahead and consider all the likely conditions before reaching the buying decision. Here, the quality and compatibility of the materials should be your topmost priority.
Safety
Some solenoid valves are designed specifically for use in different industries. The medium’s type, condition, and purpose often dictate the right valve material or the must-have features. Solenoid valves used in the beverage industry, for instance, must meet certain safety requirements.
Cost
Every valve manufacturer has its own pricing, determined by the material used, valve type, etc. Often, high-quality materials are more expensive and will last for a long time. But this isn’t always the case. You should first begin by accessing the quality and specs of the solenoids before basing your decision on the price. Where necessary, go for an expensive valve that will serve the purpose and last longer. If you are new to the market, you can consider browsing through some reviews to compare and contact various manufacturers.
Valve Specifications
Last but not least, always check the valve specifications to ensure they meet the specific applications. Here, you want to pay attention to the following:
Working principle . Know if there is a pressure differential and choose between the three main types of solenoid valves.
Voltage . Know if DC or AC voltage is available at the installation site.
Valve size & threading . Ensure the valve size matches the system’s flow capacity. Also, the connection type (e.g. threads) should allow for an easy and tightly-secured installation.
Pressure Range . So when choosing the valve pressure values, always consider the type of medium and the system pressure.
Temperature range . Too high or too low temperatures can damage the valve components. Always ensure the temperature range of the valve matches that of the medium.
Circuit function. 2-way valves are the most common, but you can also get more ports depending on the application (e.g. 3-way valves).
How Do You Know If You Have a Bad Solenoid?
Here are some of the valve problems to look out for:
The Solenoid Doesn’t Close/Open Properly
There are several reasons why the solenoid may fail to open or close as required. The issue could be power not reaching the coil, a faulty coil, pressure differences, wrong voltage, or dirt buildup in the valve tube or seat. The extent of the valve’s failure may also depend on the type, i.e., whether direct acting or pilot operated valve.
To troubleshoot the control unit, check the power supply and ensure the voltage and frequency reaching the coil are within limits. Confirm that there’s no corrosion or dirt under the diaphragm and that the coil isn’t burnt out or damaged in some way. Also, refer to the valve manual to check that the flow direction matches the indicators displayed on the valve body.
If you need further troubleshooting, the next thing to check is the pressure differences. Solenoids have varying pressure specifications, and if the input pressure is too high or too low, the valve may misbehave. Most pilot-operated valves have some minimum pressure limits below which they can’t operate. Always check the pressure levels against those recommended by the manufacturer. If the pressure is too high, consider reducing it, but find another valve that matches the system requirements if it’s too low.
Melted or Burnt Coil
Several factors can lead to a burnt-out coil. These include a short circuit, under and overvoltage, damage to moving parts, or poor system cooling. When troubleshooting the solenoid valve due to a burnt coil, you want to start by checking the voltage specifications against the ratings from the power source.
If the voltage requirements and ratings are correct, check for any short circuit. Any fault in the solenoid circuitry or fluid leaks and moisture buildup could cause a short circuit. The other key aspect to check is whether there is too much friction or high temperatures around the coil.
Dirt buildup or bent moving parts could also cause friction, generating more heat than can be dissipated. Where possible, you should consider increasing ventilation where the valve is installed.
A Persistent Buzzing Sound
While this may not be a huge problem, it can be quite irritating or may eventually lead to more valve issues if not resolved. Often, any sound coming from the solenoid is produced by a mechanical component that’s either loose or damaged to some extent. If tightening any loose parts doesn’t solve the problem, the issues could be with the alternating current noise. The noise from vibration is normal in most solenoids. But you can choose to use a rectifier unit in the valve circuitry to filter the noise.
Choose the Right Solenoid Valve Today
If you’ve read to this point, you are now more informed than the average person. Choosing the right valve for your unique applications shouldn’t be a problem anymore. You can still ask for professional help when selecting solenoid valves, as it’s easy to get confused with the many types currently in the market.