Can someone please explain this Potter fire extinguisher dripping to me?

Can someone explain to me the dripping here. Why should there any dripping. What is causing it. It's a bit weird to me. The arrows shows the direction of water(I think) and the bottom arrow shows when there is connecting water to the outside which is dripping. If I shut down the water by pulling the brown... show more Can someone explain to me the dripping here. Why should there any dripping. What is causing it. It's a bit weird to me. The arrows shows the direction of water(I think) and the bottom arrow shows when there is connecting water to the outside which is dripping. If I shut down the water by pulling the brown handle the dripping stops.

Thanks!
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