Basically, the spring and the lever are used to press in the plug (part no 2). I need to find the force that is acting upon the welding (I painted it in red). Now I don't need you to calculate anything for me, just explain why is the free body diagram of the lever like this:
I don't understand, if the spring is pushing the lever upwards, why is the force Fb drawn downwards? I can only guess that Fb is the force inside the bolt, but still, why are they ignoring the effect that the spring has on the lever? Also, on the left side, why isn't there a reactive force that the plug has on the lever? I would appreciate if someone could help me out here.