The Max 30 lbs statement on the device is only intended to help when the device is being used for watering a potted plant.  As explained in Q9 the maximum weight of a hanging basket  where the device will have good control can be 40 or 120 lbs depending on who the device is installed in the hanging basket.  As explained in Q10, the maximum  weight of a potted plant where the device will still have good control is 207 lbs.
The 10, 20 and 30 lbs marking rings on the device are intended solely to give a guide as to where to rest the edge of a pot as the weight of the pot increases.
As explained in Q10 as the pot's weight increases, the fulcrum on which the pot rests must be moved in relation to the centre of weight of the pot, such that the weight resting on the Plant Booster device remains within it's control limits.
If a pot is, say 20 lbs, and the fulcrum of the pot is on the far side of the pot opposite the device, then the fulcrum will carry about 10 lbs, and the device will carry about 10 lbs (the sum adding up to the pot's weight).  Referring to the images below, in this case the edge of the pot should be rested more or less on the ring that says 10lbs.  For pots that are heavier, the edge of the pot on the device should be placed closer and closer to the devices' hinge.
You will know that you have located both the fulcrum and the edge of the pot on the device correctly when you are able to tighten or loosen (as needed) the wing nut such that the device is able to control water flow.
If you find that you have to tighten the wingnut too much to start allowing water through the device, then the edge of the pot is resting too far away from the hinge.  Reposition the edge of the pot a little closer to the hinge and try again.
One you have found the right spot, it is recommended  that you mark the location of the fulcrum on the pot, and the edge of the pot on the device with a small indelible ink mark.