Protectoseal fuel tank safety caps, available in southern Africa from Energas Technologies, serve as a dual-purpose device for pressure/vacuum relief as well as a flash arrester in fuel tank openings of gasoline or diesel-powered equipment such as industrial trucks, forklifts, tractors and airport support ground equipment.
Among the major sources of emissions in diesel-powered equipment are evaporative emissions, which occur when fuel evaporates and is vented into the atmosphere. This can happen while a vehicle is operating and even while it is stationary.
Among the design alternatives available to engine manufacturers in their efforts to minimise emissions is the use of a pressurised fuel tank system, which helps control evaporative emissions by suppressing vapour generation. One key element of such a pressurised fuel system is the fuel cap. The cap must be able to seal against a defined fuel tank pressure and must also be able to provide some level of vacuum relief (make-up air) as the fuel tank is emptied.
This is exactly the idea behind Protectoseal’s line of fuel tank safety caps. “Safety fuel caps are essential to the safe fuelling and control of fugitive emissions to meet Environmental Protection Agency (EPA) requirements for gasoline or diesel-powered vehicles and/or equipment,” explains Lavenda Sekwadi, Process Engineer at Energas Technologies.
Protectoseal’s line of fuel safety caps are durable, with lead-free finish and colour-coded to indicate specific industry standard storage application: RED designates gasoline and GREEN designates diesel.
Relieving into the atmosphere
The caps are designed to start relieving at fuel tank pressures between 24 kPag and 31 kPag. At pressures above the set venting point, the caps allow vapours to relieve into the atmosphere, helping to protect engine components against over-pressurisation. The cap is also equipped with a non-return valve that seals against positive pressure but allows the entry of air into the fuel tank should a vacuum develop in the tank’s vapour space.
The sizes range from 1 ½” to 4” NPS and NPT male and female connections. Construction materials are available in die cast aluminium and cast brass construction. Protectoseal fuel tank safety caps are listed by Underwriters’ Laboratories to the requirements specified in Standard UL558 (“Industrial Trucks, Internal Combustions Engine Powered”). Some models are specifically designed to help engine manufacturers meet the stringent EPA fugitive emission requirements as outlined in EPA 40 – CFR Part 89.
The compression spring latch of the fuel safety cap is manually engaged to ensure sealing of the large cap opening at low pressures, while also providing automatic pressure relief if the tank pressure increases beyond normal limits, preventing tank rupture. “The cap is self-closing due to its hinged design which provides vacuum relief to facilitate flow while controlling fugitive emissions at positive pressures below the relief setting. A torsion spring keeps the cap permanently closed except when filling.”
The perforated metal flash arrester allows flow of liquid into the tank during filling but prohibits entry of an external flame into the connected filling pipe. The screen also serves as a strainer to prevent particulate matter from entering the tank, this minimising fuel contamination. “Unauthorised access and theft of the fuel safety cap are prevented by a padlock which does not in any way impair the automatic pressure relief capability of the spring-loaded cap assembly,” Lavenda concludes.
