How to distinguish between solenoid-operated directional valves and proportional directional valves?

How to distinguish between solenoid-operated directional valves and proportional directional valves?

What Is A Solenoid-operated Reversing Valve? What Is A Proportional Directional Valve?

1.Solenoid Directional Valve (Switching Valve)

Solenoid directional valve we can understand as switching valve, its biggest characteristic is that the liquid flow channel it controls is either fully open or fully closed, only these two states. Figure 1 is a two-position two-way valve, the fluid flow channel is either on or off, which is a good illustration of the characteristics of a switching valve.

 

 

Figure 1 Two-position two-way solenoid valve


In daily life, we can also find examples corresponding to switching valves, such as the switching of fluorescent lamps. The action of the switching valve is similar to the switch of a fluorescent lamp, the light is on when the switch is on and off when the switch is off.

As shown in Figure 2, it is a Bluetooth controlled light bulb, isn’t it fun.

Figure 2 light bulb switch


2. Proportional Directional Valve (Continuous Adjustment Valve)


In the proportional directional valve, the output quantity proportional to the input signal is the displacement of the spool.

The larger the input signal, the larger the displacement of the spool, the larger the corresponding opening of the valve port, and the larger the output flow rate in the case of a certain differential pressure at the valve port

(For example, the first quadrant in Figure 3, the horizontal coordinate is the input voltage, the vertical coordinate is the output flow rate, and the two are linearly related).


So we can change the flow rate through the valve port by changing the size of the input signal. This means that the proportional directional valve is essentially a flow control valve.

 

Figure 3 Polarity of the input electrical signal
Figure 3 Polarity of the input electrical signal


The above is the flow control function of the proportional directional valve, then its directional switching and how to achieve?


We know that in addition to the size of the input signal can be adjusted, its polarity can also be changed, we are using the positive and negative changes in the input signal to change the direction of liquid flow (for example, in Figure 3, longitudinal quadrant 1 and 2, the input signal is 0 ~ +10V, the liquid flow channel P → A phase; the input signal is 0 ~ -10V switch to P → B phase).Figure 4 of the motion picture is more intuitive!

 

Figure 4 proportional directional valve reversal process
In summary, the proportional directional valve can realize the control of liquid flow direction according to the change of polarity of the input signal, but also according to the change of the size of the input signal to control the size of the flow.


We also take fluorescent lamps as an example. Nowadays, it is more popular to use induction dimming chandeliers in home decoration, and its switch can be adjusted at will in the full-on and full-off zones, so as to adjust the color and brightness of the bulb. As shown in Figure 5.

Figure 5 Induction dimming


The Comparison Of Electromagnetic Directional Valve And Proportional Directional Valve

 

Take The Appearance Of The Comparison

Direct-acting proportional reversing valve and ordinary solenoid reversing valve from the appearance, there is no difference, to distinguish also through the product nameplate. Like the following two pictures, at first glance, you can see which is the proportional valve in Figure 6 and Figure 7, which is the switching valve? Obviously not.

Figure 6

Figure 7

Figure 7

Take The Structure Of The Valve Spool For Comparison

The spool of the solenoid-operated reversing valve is not slotted on the axis, as shown in Figure 8. The spool of proportional directional valve has various shapes of grooves along the axial direction, such as triangular, semi-circular, etc., as shown in Figure 9.


Figure 8 solenoid-operated reversing valve spool

Figure 9 proportional reversing valve spool
Figure 9 proportional reversing valve spool


Take Whether The Flow Is Controllable For Comparison

Solenoid-operated reversing valve is a switching valve, the liquid flow channel is either fully closed or fully open. If you want to adjust the flow rate, you have to match the flow control valve, as shown in Figure 10 below, the throttle valve to adjust the flow rate into the actuator. The proportional directional valve, on the other hand, comes with its own flow regulation function, as shown in Figure 11 below.

Figure 10_ Speed control circuit using a combination of solenoid-operated reversing valve and throttle valve (1)
Figure 10: Speed control circuit using a combination of solenoid-operated reversing valve and throttle valve

Figure 11 Speed control circuit using proportional directional valve alone
Figure 11: Speed control circuit using proportional directional valve alone


The Size Of The Pressure Shock Caused By The Comparison

The valve port of solenoid-operated reversing valve from fully closed to fully open, generally only 0.05s ~ 2s, in such a short period of time, the flow rate suddenly increased from zero, the instantaneous action on the load, it is easy to cause a start-up shock. The relationship between instantaneous pressure peak and switching time can be seen in Figure 12 below: the faster the speed of opening the hand valve, the higher the pressure peak.

Figure 12 The relationship between the instantaneous pressure peak and the valve port switching time


The Amount Of Valve Port Cover Comparison (this One Is Mainly Compared With The Servo Valve)

Proportional valve is a mass-produced product, it is impossible to control the size of the cover as strictly as the servo valve, otherwise it will make the cost increase steeply. Therefore, the orifice of proportional valve is usually positive cover (as shown in Figure 13), and its cover amount is generally controlled at 12%, 15%, 18%, 20% during design, and will be larger during actual processing. Finally, it relies on the fast-jump circuit in the controller to output a large output current at small signals, so that the spool of the reversing valve produces a large displacement to make its stroke go through its covering amount quickly and enter the working state (that is, the state of the valve opening) as soon as possible.

 

Figure 13 Dead zone of proportional valve
Figure 13 Dead zone of proportional valve

 

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