Pneumatic Valve vs Solenoid Valve: What Are The Differences

When it comes to controlling the fluid, you may encounter two types of control valves: the pneumatic valve and the solenoid valve. Although the tasks they perform are pretty similar, opening, closing, and controlling the flow of fluid, the methods behind how they perform these tasks differ greatly depending on their capabilities and ideal environmental conditions. When it comes to choosing between these two types of options available for installations, engineers and procurement specialists may get confused when choosing the right one. This is why we have created a detailed guide on the technical differences between pneumatic valves and solenoid valves to help you make the right choice for your industry.

1. What is a Pneumatic Valve?

Just like any other valve, a pneumatic valve also controls the flow of fluid. The major difference that lies between a manual valve and a pneumatic valve lies in how the torque is applied. A manual valve uses motors and gears, or sometimes torque is applied manually by hand to open the valve or direct the flow, whereas a pneumatic valve uses compressed air or gas to provide the force to open or close the valve, relying on the pressure difference.

The pneumatic valve comprises three main parts: actuator, piston, and spool. To move the valve or direct the flow, a signal is sent through the pilot air to the actuator of the valve, which is often a piston or a diaphragm. This causes the air to flow into the chamber, which is often a piston or a diaphragm, forcing the piston to move by overcoming the internal spring or friction forces that help to move the rod that is connected to a spool or a poppet. This movement allows opening, closing, and shifting the direction of the fluid.

These valves are utilized in the industry where the fluid pressure is extremely high, and closing manually by hand or by a motor becomes practically impossible. Because pneumatic valves work by relying on air pressure, they can generate immense force, making them great for industries that have high fluid pressure is required to seal or open the valve.

2. Types of Pneumatic Valve

There are multiple types of pneumatic valves available that you can find on the market based on their specialized function and construction that defines their use case. Below, we have listed a few types of pneumatic valves that can help you understand what each type has to offer: 

• Directional Control Valves: These are the most common types of pneumatic valves. Their main purpose is to direct the flow of air to different paths. Based on the applications, their classifications are often done by the number of ports and switch positions, for eg, 5/2-way, 3/2-way valves.

• Non-Return Valves (Check Valves): These allow compressed air to flow in only one direction, preventing backflow, which could damage the compressor or other components.

• Flow Control Valves: These regulate the volume of air passing through, effectively controlling the speed of the pneumatic actuator or cylinder.

• Pressure Relief Valves: Essential for safety, these valves exhaust air if the system pressure exceeds a set safety limit.

• Shuttle Valves: These allow flow from one of two sources to an outlet, essentially performing an "OR" logic function in pneumatic circuits.

3. What is a Solenoid Valve?

A solenoid valve is a valve that purely relies on the laws of electromagnetism. The basic working principle lies in the passing of electric current through a solenoid that is coiled around the plunger.

The working mechanism involves creating an electromagnet. When the current is passed through the ferromagnetic core or plunger, it creates a magnetic field around it. This causes the electromagnetic metal to pull the plunger upwards, overcoming the resistance provided by the spring, which causes the valve to open instantly. When the current is cut off, the magnetic field disappears, and the internal spring slams down the plunger, closing the valve.

Solenoid valves are often the nerves of automation in the industry. They receive signals from the PLC or a computer, which makes the decision whether the tank is empty or full, and the solenoid valve converts those electrical signals into physical ones, opening or closing the valve. They are great in areas where speed and precision are an utmost priority.

4. Types of Solenoid Valve

Typically, the solenoid valves are classified into two main categories based on how they handle pressure.

• Direct-Acting Solenoid Valves: This is the type where the magnet does all the work. The magnetic force generated by the solenoid pulls the plunger to open the valve. This feature allows the solenoid valve to work independently of the fluid pressure, making it great for low-flow, low-pressure applications or vacuum conditions. However, if the water pressure is extremely high, the magnets may not be strong enough to lift the plunger.

• Pilot-Operated (Indirect) Solenoid Valves: These types of solenoid valves are great when the magnets are weak, and you want to open the valve. It works by a solenoid creating a small pilot port or a leak, which then utilizes the water pressure for opening the valve. These pilot opeareted solenoid valves are great where there are high fluid pressure applications. However, if there is low pressure, these solenoid valves may not function.

• 2-Way vs. 3-Way vs. 4-Way: Just like a pneumatic valve, solenoids can also be classified by ports. A simple 2-way solenoid valve performs the operations of shutting on and shutting off the valve. A 3-way and a 4-way valve can be used to control cylinders or actuators.

5. Solenoid Valve vs. Pneumatic Valve: Which is Better?

When it comes to choosing a winner between the two types of valves, either a pneumatic valve or a solenoid valve, the difference lies greatly in what are the specific requirements and applications in the industry, which include safety, power availability, and force requirements.

Advantages of the Pneumatic Valve

• Safety in Hazardous Environments: Since they operate on air, there is no risk of electrical sparking at the valve site. This makes them the standard choice for oil and gas, mining, and chemical industries (ATEX zones).

• High Force Capabilities: Pneumatic actuators can generate significantly more torque/force than standard solenoids, allowing them to control very large pipes and high-pressure lines.

• Durability: Pneumatic components are robust. They can tolerate higher temperatures and dirtier environments than delicate electronic coils.

• Cost-Effective at Scale: If a facility already has a central compressed air system, adding pneumatic valves is often cheaper than wiring individual power lines for electric actuators.

Advantages of the Solenoid Valve

• Speed and Precision: Solenoid valves have incredibly fast response times, often measured in milliseconds. This is crucial for applications like sorting machines or dosing systems.

• Ease of Control: They interface directly with electronic controllers like PLCs and IoT devices. There is no need to convert an electrical signal into an air signal first.

• Compact Design: Solenoids are generally smaller and lighter than a pneumatic actuator setup, which requires the valve plus an actuator.

• Energy Efficiency (at point of use): While holding a solenoid open consumes power, they do not require the constant running of an air compressor, which is notoriously inefficient in terms of energy conversion.

6. Integrating Both Valves in Solenoid-Pilot Pneumatic Systems

In the case of complex industrial processes, particularly the ones with high flow rates like power plants, oil refineries, and wastewater treatment facilities, you need solenoid-pilot pneumatic systems. The question in such applications is not which valve is better but how they can work together.

Most industrial solenoids work at high-speed for on/off control. However, they lack the force to move heavy industrial valves. Therefore, they use a small stream of air that triggers the pneumatic valve. While a standard solenoid is either fully open or shut, a pneumatic valve paired with a positioner can float at a 25%, 50%, or 75% opening with smooth, precise graduation.

Engineers combine the use of both valves to achieve an instant electronic response of the solenoid to provide a massive modulating mechanical force for a pneumatic actuator.

8. Conclusion 

When it comes to choosing between a pneumatic valve or a solenoid valve, it doesn't always come down to which technology is better, but rather which one fits best with your industry requirements.

• Choose a solenoid valve if you want speed, precision, direct electrical integration, compact size, and your application involves working with smaller sizes of pipe and in standard conditions.

• Pneumatic valves can be best suited for applications that involve high force requirements, operations that include hazardous or explosive conditions, and require controlling the flow of fluids in large industrial pipelines.

Having a clear understanding of the differences between the two types of valves is key to selecting the right choice that best suits your industrial application. This ensures that your automation system runs safely, efficiently, and cost-effectively.

Once you have decided between the pneumatic valve and the solenoid valve, the last step involves choosing a partner or a supplier that understands your industrial applications. Our recommendation would be to go for Titan Automation. They have a premium range of directional control and automation valves that are best suited to your specific industrial needs, ensuring that you have the right valve for every challenge.

9. FAQs

Q1. Are Solenoid Valves More Expensive Than Pneumatic Valves?

It typically depends upon the size and application of the industry. Generally, for small sizes that are under 1 inch, solenoid valves are known to be cheaper and easier to install because they don't require the use of an air compressor system. However, when it comes to large industrial valves that are 4 inches or above, solenoid valves are comparatively expensive and heavy. In such applications, a pneumatic valve setup is considered a more cost-effective option.

Q2. How Quickly Do Solenoid Valves Respond Compared To Pneumatic Valves?

The opening and closing of a solenoid valve is almost instantaneous, typically taking about 5 to 50 milliseconds. A pneumatic valve is also considered fast, where opening and closing take about 100 milliseconds to several seconds, all depending upon the length of the air tubing and the volume of the actuator.

Q3. Can Solenoid Valves Be Used With Any Type Of Fluid?

Not necessarily. The fluid must be compatible with the material of the solenoid valve, which is typically brass or stainless steel, and the seal materials, which are typically NBR, Viton, and PTFE. Furthermore, typical solenoid valves are not great at handling dirty fluids or slurries, as some of the particles may get stuck within the magnetic plunger area. It's not recommended to use solenoid valves in hazardous or explosive conditions. In such applications Pneumatic valves are generally considered better and more forgiving to the flow of such demanding fluids.

Q4. How long is the life of a pneumatic valve?

The measurement of the lifespan is typically measured in cycles. Typically, a pneumatic valve that is of high quality can last between 10 to 50 million cycles, all depending upon the types of application and fluid it is carrying. The life of a pneumatic valve exceeds that of a solenoid valve due to the solenoid coils being burned out over a period of time.