Pressure Relief Devices Recalled

By Kasia McBride, Marketing Manager, NGVi 

Recently, more than 67,000 pressure relief devices (PRDs) used in CNG fuel systems were recalled by Circle Seal Controls, which is a unit of CIRCOR Aerospace. The issue was reported last year by Hexagon Lincoln, after one of its customers, New Flyer, noticed a leak. This leak was traced to a PRD failure after the outside temperature dropped below -13°F. The recall, issued by the National Highway Traffic Safety Administration (NHTSA), applies to valve models 8100-11-T1T1, 8100-37-BB, 8100-44-BB, 8100-77-BB, 8100-84-BB, 8100-94-BB, and 8100-97-BB, manufactured between July 2011 and December 2013. 

PRDs are mandatory safety devices located at one or both ends of CNG fuel cylinders. Their purpose is to protect the cylinder by relieving its pressure if it becomes excessive. Since pressure increases as the temperature increases, these PRDs are designed to activate at a specified temperature. They will rapidly vent fuel from the CNG cylinder before it ruptures from over-pressurization, such as in the event of a fire.

According to NHTSA, the defective valves have O-rings that could fail in cold temperatures between -10 and -5°F. Additionally, if the cylinder is fully emptied and then refilled, the O-rings may fail at temperatures of 20°F and below (this is more likely to happen in bi-fuel or dual-fuel vehicles which may run their CNG tanks empty and then switch to gasoline or diesel before refilling with CNG).

Ultimately, the O-ring failure could cause natural gas leaks from the fuel tank, which if in the presence of an ignition source, could increase the risk of fire, especially when the vehicle with the leak is parked in an enclosed environment.

The NHTSA report states that, “Circle Seal will notify the CNG tank manufacturers of the defect. Vehicle owners will likely be notified by either their vehicle manufacturer or by the supplier of the CNG kit, as applicable.”

The affected valves in dual-fuel vehicles will be replaced free of charge. Faulty valves in dedicated vehicles that were originally sold in, or are currently registered in, the cold-weather states including Alaska, Colorado, Connecticut, Idaho, Iowa, Illinois, Indiana, Massachusetts, Maine, Michigan, Minnesota, Montana, Nebraska, New Hampshire, New York, New Jersey, North Dakota, Ohio, Pennsylvania, Rhode Island, South Dakota, Utah, Vermont, Wisconsin, and Wyoming, will also be replaced. The valve replacement is expected in fall 2014.

Because ensuring the integrity of the NGV fuel system is the core of NGV safety, routine inspections of the CNG fuel system, including examining PRDs, are required at least every three years or 36,000 miles, whichever comes first. It is imperative that NGV technicians know how to check PRDs for leaks and cracks, inspect their vent side for trapped water or debris, and be able to identify defective PRDs.

NGVi strongly recommends that all CNG maintenance technicians be trained to perform these inspections and use proper procedures. NGVi’s CNG Fuel System Inspector Training helps ensure that technicians are adequately trained to knowledgeably inspect CNG fuel systems, detect and assess damage and determine necessary next steps. It prepares inspectors to recognize conditions which, if left undetected, could result in life-threatening situations.

If you would like to know more about this recall, contact the National Highway Traffic Safety Administration Vehicle Safety Hotline at 1-888-327-4236 (TTY 1-800-424-9153), or go to

For more information about NGV training, visit 

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