Plentiful in North America and relatively inexpensive, natural gas produces 30 percent fewer greenhouse gas emissions than gasoline or diesel, making it an ideal alternative fuel for a diverse range of applications. Heavy-duty vehicles, such as refuse trucks, Class 7-8 trucks and buses are the largest users of this fuel source. Given this growing change, the need for reliable leak-free connections is even more important which is why Parker developed a CNG version of its Seal-Lok O-ring Face Seal (ORFS) fittings.
Why Seal-Lok O-ring Face Seal Fittings?
Known for proven leak-free connections, Seal-Lok ORFS fittings have many benefits for these CNG applications. The ORFS design provides unlimited reusability, resistance to vibration, zero clearance for easy assembly and replacement, as well as resistance to overtorque which has been known to be an issue for other fittings designs. Though ORFS fittings have traditionally been used in industrial hydraulic applications due to the elastomeric seals, the creation of a special CNG O-ring has now made this reliable connection a viable option in alternative fuel applications.
Ensuring fire safety on natural gas vehicles
Since the available amount of energy per liter of natural gas is low compared to the traditional fuels, it is compressed to a pressure of at least 200 bar (2900 PSI). Therefore, special attention must be paid to the safety aspects related to CNG Cylinders on-board Natural Gas Vehicles (NGVs). One potential hazard seen in garbage truck operation is a load fire. Load fires are the most common type of truck fire in the refuse/recycling industry.
As you know, refuse vehicles travel in populated residential areas every day. It is critical to ensure the safety of not only the drivers, but anyone in the proximity of a NGV. The trucks are engineered to be extremely safe; however, load fires can heat the CNG storage tanks, raise pressure and introduce the risk of a rupture occurring. To reduce the risk of a rupture in the event of a fire, the CNG cylinders must be equipped with a Pressure Relief Device (PRD). The effectiveness of this specified fire protection system must be validated in a bonfire test.
Bonfire test for Parker’ Seal-Lok ORFS CNG Fittings
Bonfire test requirements for Cylinders and PRDs are defined in Regulation 110, ANSI/CSA NGV 2, and CSA B51 Part 2, however, there are no specific bonfire test requirements for the fittings and seals connecting CNG tanks to the system. Given the growing use of Seal-Lok O-ring Face Seal CNG fittings in these connections, Parker felt it important to develop bonfire testing to validate they would perform if exposed to fire.
The criteria for passing were defined using the most rigorous requirements placed on CNG tanks in ANSI/CSA NGV 2 and CSA B51: samples pressurized to 3,600 psig and exposed to a minimum of 590 °C for 20 minutes. To qualify as passing the bonfire test, all seals must have maintained pressure for at least 20 minutes after being heated. This bonfire test was performed by the outside testing facility of Southwest Research Institute’s (SwRI) Fire Technology Department.
Seal-Lok for CNG bonfire test results
Seal-Lok for CNG passed the bonfire test. Passing the bonfire test confirms that Seal-Lok for CNG meets the industry safety requirements for CNG components used in natural gas vehicles. Seal-Lok ORFS CNG fittings are the first and only fittings in the industry to be Bonfire Tested. In addition to passing the bonfire testing, these fittings are also tested and certified by TUV according to the following standards: ECE R110, ANSI NGV 3.1-2014/CSA 12.3-2014 for stainless steel and zinc nickel fittings, and ISO 15500.
To learn more about the Seal-Lok for CNG Bonfire Testing, download the test summary.
Find out more about this product line and see the available configurations on the Seal-Lok for CNG product series page. If you have any questions about this article, please post them and we will respond. To talk to Parker regarding the benefits of Seal-Lok for CNG for your application, please call 614-279-7070.
Written by John Holzheimer, applications engineer, Parker Tube Fittings Division
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