What is a Fuel Tank Vent Valve?
2 Answers
Vehicle fuel tank vent valve is a balance valve. There are two valves on the automobile fuel tank, one is the balance valve and the other is the vapor valve. When the fuel pump draws oil, the pressure inside the fuel tank decreases. When the pressure drops below 98 kPa, the balance valve opens to deliver air into the fuel tank. Gasoline is volatile. When part of the gasoline in the tank vaporizes, it will increase the pressure inside the tank. When it reaches 120 kPa, the vapor valve will open. Function of balance valve: The balance valve is a regulating valve with special digital locking function. It adopts a straight-through valve body structure with better percentage flow characteristics, which can reasonably distribute flow and effectively solve the problem of uneven room temperature in heating (air conditioning) systems. At the same time, it can accurately adjust pressure drop and flow to improve the liquid flow state in the pipeline network system, achieving liquid balance in the pipeline network and energy-saving effects. Types of balance valves: Balance valves are divided into static balance valves, dynamic balance valves and pressure-independent balance valves. Static balance valves, also known as balance valves, manual balance valves, digital locking balance valves, two-position regulating valves, etc., adjust the Kv (valve flow capacity) by changing the gap (opening) between the valve core and the valve seat to change the flow resistance through the valve to achieve the effect of flow regulation.
The fuel tank vent valve, also known as the EVAP system vent valve, is essentially a small component designed to balance the pressure inside and outside the fuel tank. I've seen it multiple times at gas stations where the fuel pump nozzle keeps clicking off during refueling—more often than not, it's because this valve is clogged. Gasoline in the tank produces vapor, and when the pressure builds up, it needs to be released. If the vent valve is functioning properly, the vapor is automatically directed into the charcoal canister for storage during refueling and later burned off when the car is running. However, if the valve gets stuck, excessive vapor buildup in the tank can cause the fuel filler neck to 'puff' out air, and in severe cases, even the fuel cap may become impossible to open. Once, my old car was left under the scorching sun, and the side of the fuel tank bulged out—all because the vent valve failed. After replacing it, make sure to regularly inspect the charcoal canister connections to prevent debris from entering the valve body and jamming the moving parts.
