# Rocket Pressure Pressing Formulas

Optimum pressing pressures for rockets using whistle type mixes:

Core burner type rockets: 6500 PSI

End burner type rockets: 8800 PSI

Square inch area of most common rocket motor tooling:

½" diameter | .196 square inches of area |

^{5}⁄_{8}" diameter | .307 square inches of area |

¾" diameter | .441 square inches of area |

^{7}⁄_{8}" diameter | .600 square inches of area |

1" diameter | .785 square inches of area |

1¼" diameter | 1.226 square inches of area |

1½" diameter | 1.766 square inches of area |

Here is a sample calculation of how to find pressing pressures when you factor in the diameter of the hydraulic cylinder on your press along with the square inch area of your rocket tool using 6500 PSI as the desired pressing pressure. We will use a ¾” diameter tool set and a 1¾" diameter hydraulic cylinder in our calculation.

Example:

.441 square inches x 6500 PSI = 2866.

Divide this number by the square inch area of our cylinder:

2866 ÷ 2.405 = 1191 pounds actual gauge pressure to achieve 6500 pounds pressure on the propellant grain.

To calculate the area of a cylinder, multiply its radius by itself then multiply by 3.1416 (the old familiar πr²).

Example:

For a 1¾" diameter cylinder, the radius is 1¾ ÷ 2 or .875 inches.

.875 x .875 = .7656

.7656 x 3.1416 = 2.405 square inches.

I have also listed the actual pressures for both the Black Powder fuels and Whistle Mix fuels for each size rocket, and they are available in this pdf file.