| 摘要 |
A vacuum operated flow control valve is disposed in the vapor vent line from a fuel tank to a vapor storage canister connected also to the engine air inlet. The valve has a diaphragm operator of low permeability which is biased normally open to permit fuel vapor to flow from the tank to the canister during engine shutdown. Upon engine startup a vacuum is drawn in the canister and the flow control valve which closes preventing vacuum being drawn in the tank thereby preventing tank collapse. During engine shutdown, if an ambient temperature drop creates a vacuum in the tank, the flow control valve closes; however, an emergency umbrella relief valve opens permitting reverse flow of vapor from the canister to the tank preventing excessive vacuum in the tank.
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