You should never stretch or try to compress the springs in the PowerLung as these are calibrated and any changes you make will likely cause the PowerLung to function improperly and void your warranty.
First go to the PowerLung website (www.powerlung.com). From the top menu bar select Customer Support, then User Instructions, then Resistance Cell Sets. (You can download them for future use if you want.)
The instructions for Resistance Cell Sets provide you the information to be sure your Resistance Cells are completely assembled correctly. Once you have done these steps, if the problem re-occurs, you can contact PowerLung for other remedies. Specifically Warranty, if you registered your product for warranty or Repair Service.