Valves are a common part of a control system that regulates an important process variable. These variables may include pressure, level, temperature, flow, and more.
These devices are used in many industries and applications, including oil and gas, chemical processes, food and beverage, pharmaceutical, giải pháp giám sát điện năng, marine, and water and wastewater treatment. They can be pneumatically operated or electrically actuated.
Pneumatically Operated
Pneumatically operated electric control valves work by applying air pressure to a piston or diaphragm. These valves are commonly found in chemical and fertilizer factories where they are used to control the flow of gases.
There are two types of pneumatically operated valves: direct acting and internally piloted solenoid valves (Figure 2A). The first type requires electricity to deliver the force required to open or close the valve.
The second type uses a separate air circuit that is integrated into the valve through an extra port. This method of operation allows a lower power consumption than the direct acting valve and is often used in applications where the pressure in the line can be limited, such as a vacuum pump.
Valves usually have 2, 3 or 5 connections which are also called ports. These ports are for supply, working and exhaust. They are typically manifold mounted with a minimum of two ports to provide power and work and a third port for exhausting the van an toàn or actuator.
Electrically Operated
The van bi điều khiển điện work by using an electrical motor to provide torque to move a valve. They are quiet, non-toxic and energy efficient. However, they require an electricity supply to operate and are typically used for one-use applications.
The main difference between the two types of electric actuators is their response times. Valves with a high response time are often more expensive, so if it is a requirement for the application, it needs to be taken into consideration with other specifications such as operating torque and speed.
A fail-safe feature is often available in electric actuators that will close or open a valve in the event of loss of power. It can be achieved through a spring mechanism that shuts off the valve when power is cut, or with a backup battery system.
The safety of electric valves is often a concern for plant operators, especially in process-control plants. These facilities can often be operated for decades, so a reliable actuator that doesn’t malfunction or leak toxic substances into the environment is crucial.
Combination of Pneumatic and Electrical
In some applications, a combination of pneumatic and electric control valves can be used. Usually, the choice is made based on available air supply and space requirements for installation.
For instance, in a manufacturing environment where compressed air is readily available, a pneumatic system can be used to power the control valve. This will be a better option than using an electric valve actuator in this application, since it will be more portable.
The most common type of directional control valve is a 3 2 valve. This number indicates how many ports and possible mechanism positions are present in the device.
A 3 2 valve has a minimum of three ports and a maximum of two. It also has at least two spool positions, which can be changed by an electrically activated solenoid.
The solenoid actuates the valve, opening or closing it depending on the signal. When the solenoid is not energized, a core spring returns it to its original position.
Combination of Electrical and Pneumatic
There are a number of different types of electric control valves that work in tandem with pneumatically operated valves. This combination can be a great way to control and monitor valves without having to use a controller or PLC.
One type of electric valve is the solenoid valve. When activated, the coil within the solenoid creates a magnetic field that causes the plunger to move to close or open the valve flow.
This type of valve is usually used for small flow rates and operating pressures. However, engineers are often able to develop customized solenoids for specific applications.
Several key specifications define this type of valve, including port size, thread style, and coil rated voltage. In general, each manufacturer characterizes their valves differently, so it is important to shop around and determine the product that best meets your requirements.