Technical Stuff » Spring force
Example: One liter water (1 kg) standing on the ground will apply a force of 9.81N. The formula for that is: 1kg * 9.81 m/s2 (Earth Gravity) = 9.81 N
Figure 1: The base part of the extender, a measure cup and a 1.5l PET bottle is needed
For the force test three items are necessary: A measure cup, a 1.5l PET plastic bottle and the standard base of the extender. The first step is to screw the left handed screw tight to the plastic frame so it can’t fall sideways anymore. After that I filled the bottle of water with 100ml water and place it on top of the spring-loaded piston. I repeated this procedure until the piston edge had met the first ring.
Figure 2: 350ml = 350gram + 50gram bottle = 0.4kg = 3.9N (0.4kg * 9.81 m/s2)
Figure 3: 550ml = 550gram + 50gram bottle = 5.9N
Figure 4: 750ml = 7.8N
After this test I can finally say what those lines on the pistons mean. The spring load of one piston has a range from 0 to 7.8N. Both pistons together equal a force for max 15.6N. Compression beyond the last ring will cause infinitely force as the metal of the piston meets the metal of the compressed spring. The user should avoid that stage in any case.