The new boom, fully raised and fully extended.
This movie shows the crane boom being lowered. Thanks to the restricted outlet and the four pistons, the boom comes down relatively slowly.
In the stock model, there are two air hoses connected to the switch: one from the pump, connected to the common of the switch and one to the cylinders, connected to one end. I swapped the two and added a third one teminated by the loop shown in the picture. Not visible is a pin hole in the hose that let the air out very slowly.
Here is the crane with its longer boom. Adding eight studs brings the hook ahead of the cab like on most real mobile cranes.
A close up of the boom. Notice that I've added one group of cross braces (one by four Technic beams) just to the left of where the pneumatic cylinders are attached to the boom.
This picture shows the new boom fully raised. I modified the geometry ofthe cylinder attachment points so the boom can be raised further. As a result it does not go below the cab roof anymore.
This close up shows the four (instead of two) cylinders. Adding two cylinders reduces their overall speed and double their holding power. Even with this change, the pneumatic system remains the weakest point of the crane.