A proportional solenoid valve is a valve used to control the amount of fluid flow by resizing the flow through a constraint. The regulated flow rate subsequently regulates the parameters affecting a process in the system, mainly surface, pressure and temperature. Other minor parameters include weight, thickness, moisture, density, pH, color and viscosity. In an automatic control valve, the limiter is driven by a control signal called an actuator. A proportional solenoid valve uses a solenoid valve as an actuator for different valve positions.
The standard two-way solenoid valve works exactly the same as the proportional solenoid valve, except that the former operates through a wide range of valve positions, while the latter provides only two switching modes (ie on / off), as shown below. A proportional solenoid valve with direct operation is a limiting plug.
Proportional solenoid function
In principle, the plug can be controlled with variable voltage DC, but in practice static friction on the guide points of the plug breaks the sensitivity of the valve, which leads to more residual effects (a phenomenon in which the amount of a physical property of the effect changes). Is behind). To prevent static friction, the normal input signal can be converted to pulse width frequency voltage (PWM) signal using special control electronics.
Pulse width frequency (PWM) is a method that is often used to control the power supplied to electrical devices. The average amount of voltage (and current) applied to the solenoid valve is controlled by turning the power switch on and off quickly (Figure below). This type of control puts the piston in a very fast but weak range oscillation. Puts the swingarm oscillation in a balanced position that maintains its constant sliding friction. The oscillation motion of the logger has no effect on the fluid flow behavior.
The brighter the switch compared to off periods, the more energy goes to the solenoid valve. The duty cycle The term describes the ratio of clear time “t1” to cycle time. A low duty cycle corresponds to a low power, because most of the time the power is off. The duty cycle is expressed as a percentage, it is 100% clear.
In a closed solenoid control valve, with zero current fed to the coil, it pushes the piston spring down to a fully closed position, thus keeping the valve close. Applying current to the coil creates a magnetic field to move the piston upwards against the return spring. At 100% duty cycle, electricity is fully fed to the solenoid and the valve is kept open. The duty cycles vary from 0 to 100% of the valve flow proportionally. For example, a duty cycle of 50% powered by a spring and piston solenoid transfers to 50% of the operating range.
Criteria for choosing a proportional solenoid valve
In continuous flow applications, choosing the right valve size is much more important than on / off valves. By adjusting the orifice a lot, the valve can reach full flow speed in a very small opening (impact). The residual shock is then useless, which reduces the resolution and quality of the general control of the valve. On the other hand, with the size of the orifice being too small, the milk does not reach full flow. It is recommended that the pressure drop on the valve should be about 30% of the total pressure drop in the system.
For proper and accurate control performance, solenoid valves must be configured and selected to suit their specific purpose. The most important parameters for selecting an electric control valve are the amount of kV (given in m3 / h) and the application pressure range. The lower the orifice of the valve or the stronger the coil, the lower the pressure of the valve. The maximum required kV is calculated based on the measurement formulas in the figure below.
QN = Normal flow rate [m3 / hour]
Kv = hydraulic agent
T = Inlet gas temperature [K]
p1 = inlet pressure [load]
p2 = outlet pressure [load]
dp = differential pressure [load]
SG = specific gravity (air = 1)
Based on the calculated KV value and the planned program pressure range, a suitable valve type and required opening can be determined. Please note that milk kVs should be approximately 10% higher than the program kV.
Other selection criteria to consider are maximum operating pressure, fluid, power consumption, material compatibility, response time, media temperature, operating voltage, and port connection.
Application of proportional solenoid valve
Torch / Flame Control : Two gases must be controlled in the burner control system. Both are in good proportions with each other. The ratio of combustion gas to oxidant gas, such as air, oxygen and air, is determined by the flame required for the process. Pressure level control (flow pressure control) Atmospheric pressure control is one of the possible types of surface control. Through two electric control valves, a PID controller provides enough air or nitrogen to maintain a constant pressure similar to that of liquids, which changes as the fluid pressure decreases by removing part of the liquid.
Cold and hot water mixture : Pt100 temperature sensor measures the water temperature of the mixture. The temperature controller adjusts this temperature to the given reference value by controlling the two electric control valves accordingly.
Temperature control : An electric control valve can adjust the cold water source to the heat exchanger according to the process water temperature measured. If this is higher than the reference value, more cold water is needed. If less than the reference value, less cooling is required. The heating circuit works in a similar way.
Flow control : For example, an electric control valve can be used directly as a control valve.
Actuator control (static pressure control) : Two electric control valves can control the air for the pneumatic drive (piston valve, cylinder, etc.). A PID controller determines which of the two valves should open. The control electronics adjust the drive through the solenoid valves to match the amount of process to the set point.
Ejectors / Pressure Control : An electric control valve can control the propulsion gas flow rate. More propulsion gas creates more suction power and a deeper vacuum in the suction line. The controller adjusts the valve according to the vacuum pressure.
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