Description
Designers have achieved this effect by sealing the piston of the dual-action ball pump in the cylinder at both ends. More precisely, the double action pump has two pairs of check valves: one below the piston and one above. Thus when the piston is pulled up, air is admitted to one side of the piston and expelled on the other side. When the piston moves down, the valves switch to the opposite positions, admitting air above the piston and expelling it from below.
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