The New Gas Tank and Radiator Caps
Note: This picture is stylized in order for you to see the components that make up the caps. Actually, there isn’t a huge contraption on the inside of your cap!
The old grey radiator cap ain’t what she used to be – and the same goes for the gas tank cap. They’ve grown up to be intricate, little precisionunits.
Take the gas tank cap. For a long while we’ve known about the gasoline loss by evaporation through the breather hole in the cap. Not to mention the gas that spilled out of Cull gas tanks as vehicles were parked or driven up or down steep grades, jounced over rough terrain, or simply sat in the sun so that heat expanded the gasoline and forced it out of the gas tank vent.
Well now, along comes the twin—valve gas tank cap — called twin—valve simply because it has two valves. The first of these is a blow—off valve. You see, gasoline gives off a vapor which in days of yore, used to wander through the breather hole in the cap and get lost. With the new cap, a pressure of 3 pounds above atmospheric can be built up in the fuel tank before the blow-off valve lets go. This pressure saves gas and prevents vapor lock between the gas tank and the fuel pump in hot weather. When the pressure rises above the three pound limit in the tank, the valve lets go and the dangerous pressure phtttttts.
ABHORS A VACUUM
The second valve guards against vacuum in the gas tank. On a cool day as gasoline is drawn into the engine, vaporization in the tank is not rapid enough and a vacuum occurs. Ever throw your lip around a bottle of pop and try to suck the drink. Same thing happens in the gas tank — just as it did when chewing gum was plastered over the breather hole, in the old fashioned cap. Vacuum means no flow of gas through the lines. No flow – no go. But here the second valve steps in. As soon as pressure inside the tank falls below atmospheric pressure, the little spring of the valve gives in. It’s like knocking the props out from under — atmospheric pressure pours in.
The same principle of “twin valves” operates the new radiator caps. A one-way valve allows a tree flow of air into the radiator and checks the evaporation or accidental spilling of water or expensive anti—freeze. Another one—way valve relieves excess pressure from within the radiator.
While we’re on the subject of caps, we might mention the new anti—theft, anti—loss anchor for gasoline, radiator and oil filter caps. This is simply a chain attached to cap with a ring that fits down in or some such anchor in the filler neck.
Great stuff for just before inspection – when all the tank caps used to pick themselves up and go for a walk.
From Army Motors, Nov 1941.