Hall Consulting's
Gas Gun Design Tool

Cv/Kv/Eff Calculator

While GGDT is primarily intended to help with the design of a gun, getting useful data on many commercial valves (let alone home-made valves!) can be difficult if not impossible. With this in mind, GGDT includes a tool that determines nominal valve flow characteristics based on empirical data. Granted, by the time the data is obtained the gun has already been built so it's a bit late to use GGDT for that gun's design. However, knowing the characteristics of a given valve can aid in the design of 2nd generation guns or perhaps predict gun behavior for as-yet untested ammunition.

Operation of the valve flow coefficient is simple. Once the user has the gun modeled in GGDT (neglecting "best" data for valve flow) the user opens the Cv calculator tool (accessible via the Tools pull-down menu), enters the required test data, pushes the button, and waits for the results. And yes, there may be a wait involved; the Cv Calculator is GGDT's most CPU intensive feature. Meaningful answers may take as much as a couple minutes depending upon the size of the gun and the number of data points entered (1-5 are allowed).

For each data point, the pressure to which the reservoir was charged before the gun was fired.

For each data point, the velocity at which the projectile exited the muzzle.

For each data point, the valve flow coefficient that results in a simulation data that matches the input test data.

The average value of the valve flow coefficients deterined. Note that this value is automatically transfered to the valve flow coefficient text box in the main window.

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