To solve this problem, we must first understand the role of the solenoid valve. Because the valve is driven by electric power, there is a certain difference between its structure and the pressure - driven valve. It not only realizes the glue transportation, but also has the function of glue back suction, and its structure is very simple. It only needs the pump body and the driving device, and it can make the dispensing valve with stable structure and convenient replacement. The solenoid valve and the LED glue dispenser have superior performance compared with the dispensing valves. It is usually the use of air pressure driven glue valve. The pneumatic point glue valve is made up of cylinder, valve body and material cylinder. The structure is much more complicated than the solenoid valve, and the pneumatic drive can not control the glue precisely, so it can't be compared with the electromagnetic valve driven by electricity. Therefore, solenoid valve has better dispensing performance. It can improve dispensing precision of LED dispensing machine, but electromagnetic valve also has some disadvantages. As the solenoid valve solenoid valve type LED dispensing machine is driven by electric power, so that the manufacturing cost is more expensive than the pressure dispensing valve, solenoid valve to use more advanced technology have to import, it needs to spend more money to purchase, increase the cost burden, is not suitable for small and medium production the usual dispensing operation line.