1.  Field of the Invention
This invention relates, generally, to devices and methods for puncturing a gas cartridge membrane.  More particularly, it relates to an inflation system that harnesses the force of gases escaping from a small initial puncture in the membrane to make a much larger subsequent puncture. 
2.  Description of the Prior Art
Gas cartridges contain gases such as CO.sub.2 under pressure and are used to rapidly inflate inflatable articles, i.e., when a gas cartridge membrane is pierced by a movably mounted puncture pin, the compressed gas flows at a high flow volume into a life jacket, a raft, or other inflatable article. 
Since the gas is under considerable pressure, the membrane must be made of a strong material.  Thus, the force required to puncture it is also considerable.  In most devices for puncturing such membranes, a powerful spring is employed to provide the bias needed to drive a puncture pin into the membrane.  The devices, known as inflators, provide a housing for the puncture pin, a spring or other bias means for driving the puncture pin, an activation device that releases the energy of the bias means when activated, and a channel for directing escaping gases into an inflatable article.  There are many forms of activation devices, including, but not limited to, a cam, a push button, an electric solenoid, or a moisture-sensitive pad that collapses when wet. 
There are a number of problems associated with the use of springs as the motive force for a puncture pin.  For example, over time a loaded spring gradually loses some resiliency, i.e., the metallic molecules under stress gradually realign themselves to reduce the stress with the result that a long-cocked spring will unload with considerably less force than it would have at an earlier date.  If the force has fallen below the threshold required to puncture a gas cartridge membrane, the device fails to perform its intended function.  Moreover, a spring unloading its bias exerts its greatest force at a certain point in its stroke; it has much less power towards the end of its stroke.  As a result, a puncture that was started with sufficient force may end under insufficient force, thereby curtailing the effectiveness of the inflator. 
Moreover, many inflators contain pad-like elements that collapse when wet, as mentioned above; these moisture-responsive elements are used to hold an inflator spring in its loaded configuration so that the spring automatically unloads when moisture is admitted into the inflator, thereby indicating that the life jacket or raft or other inflatable article should be inflated.  Unfortunately, the pressing of a spring against such an element stresses the element and shortens its effective lifetime.  The unrelenting pressure of the spring weakens the element, making it subject to failure and reducing its reliability, e.g., making it susceptible to collapse under conditions, such as high humidity, where it should not collapse. 
Springs fail for many reasons as well, i.e., they become corroded, especially in air where the moisture is from salt water, they get stuck if misaligned by a bump, and so on. 
It would therefore be beneficial if an inflator could be developed that did not rely entirely on a spring for all of its functions.  Such an inflator would puncture gas cartridge membranes with more reliability than spring-reliant mechanisms.  Such an inflator would also lengthen the effective lifetime of any moisture-responsive element therein because such element would no longer be subjected to constant high pressure.  Moreover, the elimination of large springs would substantially reduce the cost of manufacturing inflators. 
However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in this art how the needed improvements could be provided.