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Controlling and measuring the flow rate of Hydrogen and Helium

Monday, September 26, 2022

Customer Request: To control and measure flow of He/H2

Goal: Injecting precise amount of Helium into a balloon – enough to generate lift.

Operating parameters:

  • Process gas: Helium/hydrogen
  • Maximum flow rate: 250 SLPM to control and 1500SLPM to measure
  • Method of communication: Display

Ambition: Sending a balloon on course across the Atlantic

A team had an aspiring goal of sending a weather balloon on a course across the Atlantic Ocean. This means the balloon would be required to maintain a precise level of altitude - long enough to ride the winds from Southern Nevada to Europe, which is an approximate distance of 5500 miles.

Challenge: Filling balloons in the field

A clear obstacle is determining the correct level of hydrogen or helium gas to add to the balloon.

Filling a balloon with too little gas does not generate lift. Filling it with too much can cause the balloon to burst before reaching the target altitude, or to fail to become neutrally buoyant before bursting. To complicate the matter, due to the properties of the gasses, a balloons volume will approximately double for every 4572m of altitude achieved.

Teams are encouraged to create solutions to the challenges associated with the launching of the weather balloons. Each balloon is fitted with precise instrumentation for locating, imaging, and experimenting at target altitudes, it is the team’s job to make ensure it gets to the target location.

With over 17 launches in a two-year span, teams have had to come up with a creative solution which led them to products manufactured by Alicat.

Helium Vs Hydrogen


  • Hellium is safer than hydrogen
  • Hellium is more expensive than hydrogen


  • Hydrogen is very volitile compared to helium
  • Hydrogen is cheaper than helium
  • Hydrogen producers greater lift

Standard method of measuring lifting force of gas

The standard way they measure the lifting force of a gas within a balloon is by using weights.

To begin they would fill the balloon with the designated gas, then it would be taken indoors (to remove any external factors like wind) and weights would then be added, either 0.5 kg and/or 1kg at a time. This is done until there are signs of take-off.

Measuring this way would mean the accuracy of this is +/- 0.5kg. The team involved believed there is a better solution which is where Alicat comes in.

Bespoke solution: Portable mass flow meter with totalizer

The team contacted Alicat asking for an accurate solution to measuring the flow rate of helium and hydron in the balloon. Alicat provided a solution of the battery powered high accuracy mass flow meter (MFM)

This single device helped overcome multiple challenges the team faced.

Using the on-board Composer the team where able to switch and mix gasses in the field using the 18 hour battery life of the device!

The totalizer function was added to help prevent over filling of the ballon.

Using the MB series from Alicat the filling accuracy became better by approx. 5000 times (going from 0.5kg to a couple of 10ths of a gram).

MB Series Mass Flow Meter

Alicat MB Series Mass Flow Meter

How they managed it?

The main factor to achieving neutral buoyancy at a certain altitude is to fill the balloon with the “Goldilocks” amount. Enough gas so it will achieve the target altitude, yet not so much that it bursts or overshoots the target. Neutral buoyancy is reached when the mass of the atmosphere is displaced by the balloon, is equal to the mass of the balloon itself.

Achieving target altitude
Achieving target altitude

The team used a series of complex formulae to calculate the mass of gas required for each take off. Somethings that they had to take into consideration but not limited to:
Hooks law, the elasticity of the balloon, the gas pressure against the balloon changes with temperature and pressure (this one is specifically hard to calculate: while in the troposphere, the temperature will decrease as the altitude increases however once passed this point and into the stratosphere the opposite happens, the temperature increases with altitude).

One of the youngest team members even managed to create an app to carry out various mass calculations whilst at the launch site, to make his teams launching much easier.

Conclusion, Solutions and products for this application:

  • MCR-250SLPM-D/5M, 5IN, Gas: He, TOT
  • MB-1500SLPM-D/Gas: He, TOT

Due to the successful combination of Science, Engineering, Maths and Technology; the team were able to totalize the mass of any given mix of hydrogen and helium within each balloon, produce and replicate this data during their test flights while keeping cost and safety in mind whilst achieving this.

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