Merluz

@Alasdair Ryan & Siegfried : thanks for the tips! if i try to move very slowly the valve i can ear some air that flows out, but nothing happen and the boom doesn't move. when the valve reach a certain position, all the air rapidly flows out and the boom falls down in an half a second @DLuders: thanks for the useful guide, but my pistons are working properly, in fact they can raise up the boom with no problem. problems starts when i move the valve to the "release" position, and the air came out from the pistons... the boom of the 8421 crash down at high speed wandering if there is any method for releasing the air out of the pistons in a smooth way with the use of other lego pneumatic parts... this 8421 set is something epic, but this falling boom is very annoyng... here's some photos of my modification (with some lego system bricks) to the 8421

hi guys, i'm new to this forum, just registered sorry for my bad english, i'm from italy i had just finish to build the 8421 mobile crane set, a dream that finally come true for me! but... the pneumatic parts... when releasing the valve the boom of the crane simply crash down, it's a very bad thing to see for now i have added some springs, from various old technich sets of motorbike, 2 little springs on the boom connected to the two pneumatic pistons and one big spings on the back of the cabin, that "stops" the fall of the boom before it crash on the top of the cabin it's a temporary solution, but with this mod the boom can't "crash" anymore, the two little springs block it even if it don't fall over the cabin. i would like to solve the problem in a "pneumatic way"! any suggestion for smooting the boom when fall down? i have some extra pneumatic parts to use, one more valve, some tubes, a medium piston and a pump (the same included in the set), but i have no idea how to use them... i've tried some solution, with the use of two valve e two pumps, but every time i release a valve the boom of the 8421 fall down like a dead arm thanks in advance for any suggestion... p.s. sorry again for my english