This Demonstration calculates the force needed to open a circular cover or door of an evacuated container, vacuum oven or drier, or the like as a function of the cover or door's diameter and the absolute pressure inside. The atmosphere's exerted pressure is manifested as a "vacuum pull". The results are shown graphically and numerically in kilonewtons, kilograms force, and pounds force.

Snapshot 1: large door diameter and high vacuum (low absolute pressure)

Snapshot 2: small cover diameter and high vacuum (low absolute pressure)

Snapshot 3: large door diameter and low vacuum ("high" absolute pressure)

This Demonstration calculates the force needed to open a circular cover or door of an evacuated container or chamber. It assumes that the atmospheric pressure is 100 kilopascals (kPa) and that the cover or door is hinged on one side and has a latched handle on the opposite side. Assuming that the pressure effect is equivalent to a force exerted at the center and that it takes half this force (due to the lever effect) to overcome it, the needed force is calculated from the equation , where is in kN, is in kPa and is in cm. The variables and are entered using sliders.

The calculated force is simultaneously displayed in kilonewtons (kN), kilograms force (kgf), and pounds force (lbf). The graphics show a diagram of the cover/door (not to scale) and plots of the force versus the opening's diameter and the absolute pressure inside the container or chamber.