When should the three-stage oil and gas recovery equipment be turned on?

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　　When should the third-stage oil and gas recovery equipment be activated? As efforts to improve environmental protection intensify, more and more gas stations are installing such equipment. In actual use, gas station employees generally have no trouble operating this device; however, when it comes to “when it should be turned on,” the answers vary widely. So, how exactly should it be done? It’s necessary to start by discussing the functions of three-stage oil and gas recovery. 　　In gas stations that have undergone one or two rounds of oil and gas recovery upgrades, during fuel unloading, the oil from the tank truck enters the underground storage tanks of the station, while the oil and gas in those underground tanks return to the tank truck. This creates a closed circulation system for oil and gas between the tank truck and the underground storage tanks. When a fuel pump fills a car with fuel, the oil from the storage tanks goes into the car’s fuel tank, and the oil and gas in the fuel tank are recovered back to the storage tanks through the oil and gas recovery system. Thus, a closed circulation system for oil and gas is established between the car’s fuel tank and the storage tanks. 　　At room temperature, the amount of gas that returns to the tank truck is equal to the volume of oil unloaded from it; theoretically, there is conservation of volume for both gas and liquid, with an equal-volume substitution taking place, and as a result the air pressure inside the tank does not change. But in reality, the volume of oil and gas within a gas station’s oil and gas recovery system is constantly changing: 1. During fuel loading in summer, the temperature inside the underground tanks is lower than the outside temperature. When gasoline is poured into these underground tanks, the cold gas inside them enters the fuel tank trucks. Due to the temperature difference, the volume of this gas expands rapidly. Since gas stations equipped with oil and gas recovery systems are closed systems that prevent the escape of oil and gas, this leads to an increase in pressure within the tank system. 2. In gas stations fitted with oil and gas recovery systems, the required ratio of gas to liquid is 1.1–1.2; that is, for every 1 liter of gasoline delivered to a vehicle, 1.1–1.2 liters of gas return to the tanks. This is especially true in winter, when cold outdoor air enters the underground tanks, and the gas expands again due to the temperature difference, further increasing the pressure within the tank system. 　　Both of the aforementioned processes—unloading and refueling—can cause an increase in pressure within the tank system. Therefore, it is essential to release the pressure in a timely manner to eliminate any risks. Thus, at gas stations equipped with oil and vapor recovery systems, methods such as condensation and adsorption membrane treatment are used to convert the oil vapors in the gas into a liquid state, allowing them to flow back into the oil tanks, while clean air is released outside to relieve the pressure within the oil tank system. 　　Therefore, the three-stage oil and vapor recovery equipment at gas stations should not only be used during fuel unloading but also turned on while refueling normally!