Asking about the pump heads that are pressed on the valve, not screwed. One has to lift a lever before pumping. After pumping, push the lever down before removing pump head. I would like to understand the mechanism of the pump head (not the pump itself). Google didn't help.
What I wonder about is that the pump head's cylindrical opening is loose on the (cylindrical) valve and then lifting the lever creates a tight seal between the pump head and the valve. How is this seal created? It seems difficult to narrow a cylindrical opening without something wrinkling, except with an iris valve. But an iris valve would require turning, not lever-lifting.