Questions regarding the design of the gasoline tank vent pipeline at gas stations?
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I designed one vent pipe for the gasoline tank, but the construction party said that gas stations have two vent pipes for their gasoline tanks – one that remains open and one that remains closed. During unloading, when the normally closed valve opens, it is inevitably too late to vent. Something just doesn’t seem right, and the gas station regulations don’t mention this either. Is there anyone with actual experience who can explain what’s going on? (There are three instances of oil and gas recovery.)
Presumably, it’s to prevent the breather valve from malfunctioning
Oil unloading is fast, and fuel filling is at full speed. Prevent untimely discharge of oil during venting
For gasoline tanks, two vent pipes must be installed. One of them remains open at all times; its outlet is equipped with a breather valve, which serves to equalize the pressure inside the tank during refueling and to minimize gasoline evaporation. The other pipe remains closed under normal conditions; its outlet has a flame arrester. It is opened during oil unloading or tank cleaning. During these processes, the pressure inside the tank changes rapidly, and the breather valve alone is insufficient to balance this pressure. Additionally, a diesel tank only requires one vent pipe, with a flame arrester installed at its opening; this vent should remain open at all times. Since diesel does not volatilize as easily as gasoline, and even if it evaporates through the vent pipe, it poses less of a risk than gasoline. The above applies to the secondary oil and vapor recovery system. The tertiary oil and vapor recovery system involves removing the breather valve on the gasoline tank and connecting that vent pipe directly to a gasoline condenser, with the condensed liquid then returning back into the gasoline pipeline.
The answer is very detailed; thank you so much. But there are some ideas: since the gasoline vapor cannot be released in time during unloading, could the exhaust pipes be enlarged? For example, could two 50-mm gasoline exhaust pipes be replaced with one 100-mm exhaust pipe?