Electro valves play a key role in a myriad of projects, and it is common to wonder whether they should be driven by a solenoid or a motor. If you have ever come across this question, you are in luck: in this post we will explain when you should opt for one or the other. But first, we’ll clear up what an solenoid valve is and what other types exist. Let’s get to it!
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An electro valve is an electromechanical valve designed to control the flow of a gas or fluid down a tube or pipe. They generally have two positions: open and closed. But just as with everything in life, black or white is not always the answer. Which is why proportioning electro valves that allow for infinite intermediate settings are widespread nowadays.
Electro valves are designed to be used with water, oil, gas, air, fuel or steam, among others, and they can be from two to five-way valves. In addition, they can be manufactured in tin, stainless steel or PVC depending on the fluid used.
They normally operate in three different ways, depending on their intended use:
- Direct-acting: The electrical command directly drives the opening or closing of the valve by means of a piston.
- Indirect-acting: When it receives the electrical command, the piston is driven which allows the main diaphragm to open or close as a secondary (or indirect) action. This type of valve requires a minimum pressure in order to operate properly.
- Mixed or combined: They do not require a minimum pressure as indirect-acting valves do. In these valves, the opening command takes place in two stages: first, the upper pressure of the large diaphragm is emptied, and then, the lower diaphragm pressure pushes it so that it is opened. During the second opening stage, the piston is attached to the large diaphragm by a spring, and this spring accelerates the upward pressure when opening the diaphragm.
In addition, each of these categories may be Normally Closed (N.C.) or Normally Open (N.O.), depending on whether its operation involves being closed, and opening for a few seconds when the solenoid receives the signal; or being open and having the solenoid interrupt the flow when it receives the signal.
In mixed and indirect-acting valves, the diaphragms used depend on the material that will flow through them. Diaphragms may be made out of BUNA, VITON or TEFLON since each of these diaphragms have certain features. For example, BUNA diaphragms withstand temperatures of -10 +90 °C and it is recommended for water, air and inter gas. For its part, VITON withstands higher temperatures, -10 +140 °C and it is recommended for light oil, gasoline and diesel. On the other hand, TEFLON withstands temperatures ranging between -10 +180 °C and it is recommended for steam due to the temperature it can withstand and its strength.
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How do proportioning valves work?
Proportioning electro valves allow for the control and adjustment of a fluid based on an electrical signal, which may be a current or voltage. The use of these valves in pilot electronics enhances their precision level and, therefore, broadens the fields to which they may be applied.
Their main application is controlling precision and force, since movements and proportional and precise, which allows for a more precise control of the fluid flow.
They may be classified as:
- Flow control valve: they continuously adjust this parameter between a null and a maximum value. In addition, they are slide, distribution valves, and provide a variable number of ways and positions.
- Pressure control valves: they adjust this parameter’s output, also continuously, between a minimum and a maximum value, which equals the input pressure.
Differences between motor-driven electro valves and solenoid valves
Valves are the most essential adjustment devices existing in industry thanks to their design and materials. Their functionalities include opening and closing; connecting and disconnecting; and adjusting, modulating or isolating liquids and gases. Commonly, a valve has two parts: the drive or actuator, and the housing.
While the housing is in charge of controlling the amount of fluid that flows through it, the drive or actuator is in charge of applying the necessary force to move the housing to perform the adjustment.
Among the actuators, we can find those that are driven by a solenoid, and those driven by a motor.
Solenoids are devices that can create a highly uniform and intense magnetic field on the inside, and very weak on the outside. Thanks to this magnetic field, we can accomplish a linear motion on a shaft manufactured out of ferrous materials, which will be in charge of acting on the valve’s housing.
Motor-driven electro valves commonly use single-phase alternate or direct current motors, though we could find different types of motors depending on the precision and force we require.
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Applications of motor and solenoid valves
The purpose of a solenoid-driven valve is the same as the one of a motor-driven valve, but depending on the use and application that that valve is intended for, it will be necessary to opt for one system or the other.
Usually, for applications which require a low energy consumption, we will choose motor-driven valves, since they only use energy when transitioning from one state to another, which enables us to stop them at a specific position. Additionally, for large valves it is better to use motor-driven valves, since they are much easier to implement.
Conversely, for applications in which the priority is the transition speed, solenoid valves are recommended, since the linear motion generated by the solenoid is very fast. Similarly, this device is commonly used for small valves, since it is very easy to implement.
What characteristics should we take into account when choosing a valve?
- Flow to control (viscosity, pH…)
- Pressure ranges we want to operate with
- Fluid and outside environment temperature
- Type of pipe or connection
- Electrical characteristics of the valve (voltage range of operation; DC or AC)
- Necessary force
- Operation speed
- Period of operation
As already stated, the use of one or another technology will depend on the final application and sought features.
While a motor-driven electro valve is usually employed in irrigation systems with flow or pressure control, high-pressure hydraulic lines, dental equipment and vehicle suspension systems; solenoid valves are very common in commercial cooling systems, in the control of industrial pneumatic systems, compressors, coffee makers and boilers.
The features of each technology include:
- Variable aperture (flow) proportional to the control signal
- No minimum operating pressure required
- Low energy consumption
- The valve position is maintained in case of an energy shortage
- High transition speed
- Simple construction
- Low cost
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If, after reading this article, you still have doubts about which technology is more appropriate for you, at CLR, Compañía Levantina de Motorreductores, we can help. Our team of engineers has significant experience with projects involving electro valves, and some of them have become success stories, such as the motor-driven electro valves used to adjust the force of vehicle shock absorbers, where the greatest challenge was finding a solution for which our gear motors worked at peak performance withstanding high levels of vibration and harsh external environmental conditions.