# Research Progress of Related Technologies of Electric-Pneumatic Pressure Proportional Valves
## 2 Research Status of Electric-Pneumatic Pressure Proportional Valve  
Pneumatic high-speed switch solenoid valve contains many advantages, such as small size, convenience in integrating, anti-pollution, low production costs, and high speed. It is more common for solenoid valves to be the pilot level proportional pressure valves, which are composed of a main valve, a pilot control valve, a digital controller, and a pressure sensor [8; 9; 10; 11]. The pressure sensor is used to detect the pressure of the outlet; it is a closed-loop control, as shown in Figures 1 and 2. Figure 1 is a modified polyphenylene oxide (MPPE) type electric proportional valve of FESTO Company; Figure 2 is the ITV series valve of SMC Company. There are differences between them, but the principles of both are the same. The square wave signal is controlled by the digital controller output of the electromagnetic pneumatic pressure proportional valve in Figure 3, pilot inlet valve \(a\) and exhaust valve \(b\) are controlled by square wave signal. When the intake valve \(a\) is opened and the exhaust valve \(b\) is closed, the output pressure of the pilot valve can be increased, at this time, the active valve core is pushed, and the airflow is increased due to the opening of the opened throttle, the intake port \(P\) is connected to the output port \(Pa\). Figure 1: FESTO proportional valve. (**a**) FESTO pneumatic pressure proportional valve modified polyphenylene oxide (MPPE); (**b**) FESTO MPPE proportional valve working principle diagram. Figure 3: Switch solenoid pneumatic pressure proportional valve. (**a**) Solenoid valve control circuit diagram; (**b**) Schematic diagram of switch solenoid valve. Figure 2: SMC pneumatic pressure proportional valve. (**a**) SMC ITV series electric proportional valve; (**b**) SMC ITV electric proportional valve working principle diagram. Switching solenoid pneumatic pressure proportional valve has been studied by a large number of scholars both at home and abroad [12; 13; 14; 15], among whom the most representative research is the Parker P3P-R pneumatic electromagnetic proportional valve conducted by [PERSON] [16; 17; 18]. Parker P3P-R pneumatic solenoid proportional pressure relief valve is a common market in the typical switch solenoid pneumatic pressure proportional valve, as shown in Figure 4a,b. Based on the relationship among the internal parts of the valve, the nonlinear mathematical model of the valve is established, and the dynamic behavior of the valve in the time domain and the frequency domain is studied with numerical analysis and experiments. [PERSON] discovered that when the output pressure of the pressure-reducing valve reaches the preset pressure, the two switches in the control chamber will remain closed, hence there is no excessive energy consumption. However, when the preset pressure changes, it needs to adjust the control valve in the cavity to control the pressure in the valve cavity, frequent opening and closing, and the slow response of the valve, which causes the output frequency response of low pressure valve. At the same time, the correctness of the mathematical model of [PERSON] has been verified, as shown in Figure 4c. Figure 4d is the frequency response of the valve; the results show that the cutoff frequency of the pressure relief valve is 5 Hz. When the valve reaches a frequency of 5 Hz, the pressure chamber will show instantaneous fluctuating pressure and flow and the valve precision will be affected due to the unavoidable limited movement position that is caused by valve position. Switch electromagnetic pneumatic pressure proportional valve has the advantages of consuming low energy, having a simple structure, low costs, and so on; it has obvious advantages in static pressure regulation. It is insensitive to the rapidly changing pressure signal because it has a low frequency  
Figure 4: ParkerP3P-R pneumatic solenoid pneumatic pressure proportional valve.