Ever Wonder, How Does an EVAP System Work? (Here’s a Detailed Breakdown)
ClubLexus member sacrifices a rusted Corolla in the name of automotive education, answering the question, How Does an EVAP System Work?
Without wishing to toot our own horn, Club Lexus really is a fascinating place to spend some time. We could be talking about the next generation of electric supercars one minute. Then we shift gears and drool over celebrity-owned icons the next. From there we can skip to discussing some insane Lexus builds. And now here we are giving an education about how the EVAP system in your car works. And when we say we, we mean one of our forum members known as speedkar9 provides this useful education.
A thread was posted a few years ago titled “How the EVAP System Works.” And it is still proving helpful to this day. Seriously, hit that link and scroll through all the photos. EVAP systems may seem like a rather mundane subject, but the thread is fantastically detailed with its pictures and description. A video with even more detail is posted to his YouTube channel (which you can watch down below).
Evaporative Emission Control (EVAP)
Gasoline fumes are dangerous. Not just because they are flammable but because the chemicals contained in the fumes contribute to air pollution. The EVAP system in your gasoline-powered car is designed to capture gasoline fumes and other emissions produced when fuel evaporates within the gas tank or fuel system. These vapors are then returned back to the combustion process so they can be burned and not escape directly into the atmosphere.
Rusty Toyota Corolla
What speedkar9 has done is taken the entire fuel system out of an old, rusty Toyota Corolla. He then proceeds to cut all the components open se we can see inside and how they all work. Plus, let’s be honest, it is just fun to cut things open. In any event, the main components that make up the system are the gas tank, EVAP canister, fuel filter, fuel filler tube, and various sensors, hoses, and valves.
Laying It All Out
Once all the components are removed, the entire system is laid out on the ground so we can get a better look. The first thing that speedkar9 explains is what the various hoses are for. There is a ventilation hose that will vent fumes into the EVAP canister. There is an air outlet hose that will vent to the atmosphere. And there is a purge line that takes the harmful fumes back to the engine to be burned. And a fresh air inlet that comes from the air filter. Along with a couple others. There are quite a few lines running to a relatively small canister.
EVAP Overview
At this point, speedkar9 provides a nice overview of how all the components work together to form an effective EVAP system. After the overview, the focus is on the ancillaries on the gas tank. He looks at the EVAP check valve and explains how that works, followed by the overfill check valve. He eventually cuts the valve open so we can get a good look inside and a better understanding of how it works.
Gas Tank
Now it is time to move on to the gas tank itself and cut that sucker open. For safety sake it is filled with water. Inside you will see the baffles inside to keep the gasoline from sloshing around while you are trying to achieve maximum lateral acceleration in your Corolla. If you push the Corolla a little too hard and roll over there is a one-way check valve that prevents the gasoline from escaping out the filler neck. Speaking of the filler neck, that is examined next. And when we say examined, we mean cut open. It is a fairly simple hollow tube with some vent lines, sensors and valves.
EVAP Canister
This might be the most fascinating piece of the entire system. It is basically a holding tank for the gasoline vapors. The canister is filled with pellets that look like rat turds. But it is really activated charcoal. This charcoal absorbs the gasoline vapors. There is a spring and a pad that puts pressure on the charcoal to keep it compact so there is not too much open-air space.
BBQ Time
Gasoline fume-infused charcoal sounds like the perfect fuel to cook some BBQ! (Just kidding. Don’t do this.) Anyway, that is how speedkar9 wraps up the video below. The EVAP system is simple and complex all at the same time. Most folks don’t realize all that goes into the simple act of filling your car with gas. But if you watch this video you will better understand how the system works and can impress/annoy your friends at the next car meet.
Images: speedkar9; Toyota
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