Knowing & Practicing Nitrogen Safety
Prevents Serious Injuries

The increased use of nitrogen flushing in irreplaceable linesets for HCFC to HFC equipment conversions the last few years has revealed that some HVAC/R service technicians don't practice proper nitrogen safety procedures.

Exacerbating this growing nitrogen safety concern is the emergence of flushing agent solvents packaged in aerosol canisters. These solvents are invaluable for cleaning contaminants out of irreplaceable linesets during R-22 to R-410a conversions and other types of service related issues such as burnouts. However, because they require nitrogen flushing, some service techs are endangering the work site by not observing proper safety procedures.

Most flushing agent brand aerosol canisters have a minimum burst pressure of 270 psig for Department of Transportation 2Q rating compliance. Mainstream Engineering's Qwik System Flush (QSF) canister has a minimum burst pressure of 391 psig to meet European and American standards. However, no flushing agent canister on the market can withstand the pressure from a 2,000 psig nitrogen tank. That is why all aerosol-packaged flushing solutions display warnings that remind the user not to accidently pressurize the canister by connecting the flushing agent to nitrogen source either directly or via a manifold gauge set.

Service technicians have been trained in the proper use of compressed nitrogen, but due to the numerous methods of delivering system flushes into the linesets, they may indirectly over pressurize the canister. Situations may exist where the nitrogen regulators and manifold gauge valves have leaks, and can indirectly over-pressurize the flushing agent canister if it is connected to a manifold gauge set. Human error, and untimely turning of the wrong valve, can produce the same dangerous result.

The most important instruction is never connect a nitrogen bottle to an aerosol canister or unattended sealed system either directly or via a manifold set. A flushing agent canister should never be connected to manifold gauges. There are two common safe and reliable methods to connect the flushing agent canister access valve/charging hose to the line set. One is to use a conical rubber piece with a connection fitting (sold by the manufacture of the flushing solutions). Another is to attach a ¼-inch flare fitting on to the linesets. All manufacturers specifically warn not to connect the aerosol can to a nitrogen cylinder or a manifold set.

Aerosol Canisters

Even when an aerosol canister's access valve is closed, there's the possibility of a higher pressure source breaching it, such as nitrogen via manifold gauges. Aerosol cans with re-sealable valves are opened by pressing down on a spring loaded valve. When the valve stem is retracted and not pressing down on the valve core depressor in the canister top (the valve is closed), a high pressure connected to the access valve can push the spring loaded valve down enough to allow the high pressure fluid to enter the can, where it becomes trapped. This occurs at a differential pressure of about 120 – 160 psig. After accounting for the propellant in the can, an external nitrogen pressure on the valve of something more than 240 – 280 psig will allow this high pressure to enter the can. Therefore, when exposed to an external nitrogen pressure above 270 psig, the high pressure nitrogen will flow past the closed access valve, and can cause the can to rupture.

Nitrogen Regulator

Nitrogen flushing pressures are recommended at 100 psig, which is far less than the maximum pressure capacities of flushing agent canisters. Nitrogen is wasted when flushing at pressures above 100 psig, because the additional pressure provides no additional benefit. Therefore, if a service tech ignores all product specific warnings, but does properly flush nitrogen at 100 psig, other factors can still cause a canister failure. One example is the absence of a regulator on the nitrogen source.

Another explanation lies in a conventional pressure regulator's design. Pressure regulators typically have a spring loaded valve seat. The regulated outlet pressure is set by changing the preload on the spring closing the valve to the nitrogen supply pressure. This force is balanced by the pressure of the gas exiting the regulator. Setting the regulator pressure also sets the nitrogen pressure flowing out of the regulator. However, if the nitrogen is not flowing and is sealed off, such as being connected to a sealed system or an aerosol canister, then any small leakage around the pressure regulator's valve seat will slowly increase the pressure downstream of the regulator. The problem worsens if the valve seat is damaged, worn or corroded, because the pressure rises faster. This leaking gas could be the source of pressure to the aforementioned "closed" flushing agent canister access valve.

Malfunctioning nitrogen regulators is another reason not to leave a pressurized system unattended. The new R-410a high-pressure manifold gauge sets have a required 800 psig working pressure and the new R-410a recovery tanks have a rated operating pressure maximum of 400 psig. The older manifold, hose sets and recovery tanks have a lower 320 psig rated pressure. Likewise the aerosol cans have maximum pressures of 300 – 400 psig. A nitrogen tank, on the other hand, has an internal pressure above 2,000 psig. Any nitrogen leaking past the regulator seat, into a closed system, can eventually rise above 2,000 psig. The high pressure can rupture service manifold sets, refrigerant recovery tanks, the vapor-compression system plumbing or aerosol canisters. Therefore, never connect a high pressure nitrogen source to a sealed system while it is unattended. For example, pressurizing a system with nitrogen to the nameplate pressure for the purposes of leak checking must be followed up by disconnecting the pressure regulator to record the pressure. Leaving the nitrogen connected and pressurized during lunchtime could result in a system rupture.

Anatomy of an Accident

An accident can easily occur when any of the mentioned unsafe practices and malfunctioning equipment are combined. For example, in the case of a three-hose manifold gauge set, if a nitrogen bottle (with a regulator) is connected to the center line, with an aerosol canister connected to the low-side service hose and the system to be flushed connected to the high-side service hose (with the high-side service valve closed); When the pressure rises in the center hose and manifold, due to leakage past the nitrogen regulator, it will not show on the manifold's pressure gauges, since the manifold valves are closed. Even if the valve on the nitrogen tank is closed, significant pressure still exists on the high side of the regulator between the nitrogen tank valve and the regulator. For this scenario, a potential disaster caused by a rupturing aerosol can, a recovery tank or any other sealed system can occur in one of two ways:

A small leak past the low side manifold valve can potentially increase the pressure slowly in the aerosol canister, even though the canister access valve is closed. While the manifold gauge on the hose connected to the canister will show this pressure, the service tech might overlook it because the manifold is not being used at the time. Simple thermodynamics occurs. If the pressure in the center hose and manifold is 2,000 psig, even when the volume on the aerosol can side of the manifold is four times greater, the pressure will drop by only to 25 percent of 2,000, or 500 psig, which is enough to rupture any can without warning.

Alternatively, opening the low side valve on the manifold gauge connected to the aerosol can – with the access valve on the canister top and the high side valve to the flushed system still closed – the pressure build up in the manifold and center hose will instantly raise the aerosol cans pressure above its maximum rated pressure. The service gauge will show this pressure, but if unnoticed, the canister may rupture without warning.

Free Safety Valve is Third Line of Defense

Over-pressurizing canisters, systems or gauge sets can be avoided by following two lines of defense.

1. Read all instructions from the manufacturer for safe operation and/or usage of their product;
2. Never connect a nitrogen bottle to an aerosol canister or an unattended system. Mainstream Engineering has now created a third line of defense:
3. Service technicians can retrofit their old Qwik Can Access Valve with a pressure relief valve. Simply click HERE to "Get Your Free Relief Valve" or call 321-631-3550 and ask for customer service.

Mainstream is supplying this free valve to any technician. $5.00 for ground shipment charges will apply (more for overnight delivery). This free pressure relief valve fits on the Qwik Can Access Valve (part number QT1105) for use with QSF.

This third line of defense should only be used in conjunction with the first two lines of defense, and is intended only to prevent excess pressure surges, 200 psig and above, from entering the canister. This 200 psig relief pressure is well below that of any canister in the field. Any new Can Access Valve (QT1105) manufactured after 15 July 2010 will have this safety valve installed.

The safety valve giveaway is a goodwill measure taken by Mainstream Engineering, which is absorbing the $150,000 cost. Mainstream Engineering, and Qwik Products by Mainstream Engineering, asks that those technicians and service providers retrofit any QT1105 Can Access Valve that they may use. It is the goal of Mainstream Engineering to prevent any accidents, and provide the best, and safest, tools available to the industry. These measures are well worth the costs and effort if it prevents a single nitrogen related accident from occurring.

Bio: Robert Scaringe is president of Mainstream Engineering (www.mainstream-engr.com), Rockledge, Fl., and currently has more than 70 HVAC-related patents. He has written more than a hundred articles for technical publications. Mainstream's HVAC/R service products division, www.qwik.com, includes EPA-608, EPA-609, IAQ, Preventative Maintenance Tech (PM-Tech), and Green online certification/training programs, plus products such as Qwik System Flush, a flushing agent that was originally developed under a contract for the U.S. Air Force that is now marketed through traditional HVAC distributors.