Filler Caps and Fuel Caps Information

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 Filler cap

Filler caps and fuel caps are closures for the containment of liquids or granular media within tanks, containers, or machinery. The primary function of filler caps and fuel caps is to seal the filling port to the tank. Some caps allow the tank to breathe, while others provide a complete seal. Examples of applications for filler caps and fuel caps include fuel, oil, water, hydraulic  fluid, and chemical tanks. Filler caps and fuel caps may also be referred to as oil fill caps, gas caps, radiator caps, and tank caps. Filler and fuel caps use one of several methods to close off the tank. They can use a fine or course thread, a quarter-turn connection, or use a hinged radial or face seal closure.



Materials commonly used for filling caps and fuel caps are plastic, steel, aluminum, and brass. Finishes range Filler cap from painted, as cast or molded, and polished to chrome-plated. Material selection and finish is based on corrosion resistance requirement and aesthetic appearance needs.


Size is another key specification that differentiates these products. Size is driven by the rate of fill needed and the configuration of associated filling equipment or containers.


Other features that can be found on filler caps are self-closing and the ability to be locked. Some filler caps also allow for filling the tank without completely removing the cap.


Filler caps and fuel caps are commonly used on rail locomotives, marine, aerospace  and transportation vehicles, liquid processing systems, storage, construction, mining, farm and forestry equipment.

Image credits

Morrision Bros. | Gates Corp.