Propulsion Units
Each lane is equipped with a dedicated propulsion unit, consisting of an electrically-powered air pump. One pump can service at most 3 kilometers of pipeline, so it's necessary to use several pumps on longer lanes.
The pumps must be reversible, creating either pressure or vacuum. The pumps are connected to the pipes with tee-fittings. On both sides of the tee the pipe is equipped with switches activated by a passing capsule.
At first the pump is set to intake mode, pulling the capsule towards the tee. Before reaching it, the capsule hits the first switch, causing the pump to start reversing. Meanwhile the capsule reaches the tee-fitting. As it passes the tee, the pump is already fully reversed and starts to push the capsule away.
The older pumps were bladed, having a single blade, mounted eccentrically inside a 300 mm high cylinder. More recent pumps employ a rotating piston instead.
Read more about this topic: Prague Pneumatic Post
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