Students have to build a pedal powered water pump usable if irrigation where there is little available electricity.
They used two cylinders, they should have gone for three which would have made it much easier to work.
Here both pistons would be wanting to change direction at the same time, the time where maximum effort is needed.
With three pistons, only one piston is ever at that maximum effort point, the other two being in positions of mid-travel. This set-up can lead to a much smoother process both of water flow and of pedal effort required.
The cylinders were bits of plastic tubing got from a local hardware store, the pistons just block of plastic cut to shape.