Nitrous is a gift from the gods. It's a passing gear. It makes average engines extraordinary and average hot rodders feel a foot taller when they are on the button. But like all great gifts, it doesn't last forever, and therein lies the rub: The squeeze is fun while it lasts, but what do you do when the bottle runs out? The easy answer is to run to your local nitrous oxide supplier and have them refill it. That's fine if you have a source nearby, but what if you live in the sticks or are at a racetrack that doesn't offer that service? Relax, you can do the job yourself and save a few bucks while you're at it.
Not all mother bottles have a siphon tube likes this one. Those that do usually have a paint mark at the neck of the bottle or a stripe painted down the side. If your mother bottle has no tube, you need to position it upside down or at a downward angle to ensure you are forcing out liquid nitrous and not the vapor. Stands are available to hold the larger bottles upside down.
The key to refilling a nitrous bottle yourself is to have another bottle (or two, or three if you're trigger-happy) that you can siphon nitrous from. This is commonly referred to as a "mother bottle," and you can rent or buy the larger capacity units from welding supply stores, medical equipment suppliers (though some won't sell it to you, and none will have the lower-grade, scented car stuff), or compressed gas retailers. A mother bottle can range from 10 to 100 pounds in capacity.
The bucks-down approach to refilling your 10- or 15-pound onboard bottle relies on simple physics, a little ice, and a lot of heat. Because nitrous is stored in liquid form, it sits at the bottom portion of the bottle. Vapor pressure, a result of the physical reaction of liquid changing to gas, fills the top of the bottle. Heat or pressure causes the reaction. When you crack open the valve at the top of the bottle, the vapor pressure forces the liquid up through a siphon tube and out of the valve. The rate at which the liquid is forced out of the bottle depends on how hot the bottle is and how much liquid is present, and consequently, how much vapor pressure has built up at the top of the bottle.
To force the liquid out of one bottle and into another, simply connect a hose between the bottles, use a safe (nonflame) method to heat up the mother bottle (increasing the pressure inside), then cool off the race bottle (decreasing the pressure inside). The pressure differential between the hot bottle and the cool bottle makes it possible for the liquid nitrous to transfer from one to the other. Easy, right? Use these tips and it will be.
