One of my hobbies is launching high altitude weather balloons carrying video cameras and scientific instruments to record various environmental parameters at high altitude — 90,000 to 100,000-feet. I'm planning another project and I was wondering how much pressure is being exerted inside my balloons when they get close to their burst altitude of 90,000 or 100,000-feet? The balloons use helium as the lifting gas. The amount of helium placed in a 1500-gram (the weight of the balloon itself) balloon at launch is about 270 cubic feet. The balloon's diameter when it reaches burst altitude is about 30-feet. The balloon's volume at burst, according to the HAB-HUB Burst Calculator, is about 7.59 meters cubed. I'm wondering how much force is being produced by the gas as it pushes against the opening at the base of the neck of the balloon. I'm looking to design and build a helium release mechanism to vent the balloon at altitude to slow its ascent to lengthen the amount of time that the balloon stays at close to its maximum altitude, then vent it again to start a slow descent. Any thoughts?