| 摘要 |
A dispensing pump having no check valves includes upper and lower mechanically-joined pistons which are moveable together through respective upper and lower cylinders. As the pistons are moved in one direction toward a rest position the cylinders are initially pressure-isolated and the upper piston aspirates spray liquid into the upper cylinder while the lower piston aspirates air into the lower cylinder. Before reaching the rest position the pistons unblock flow communication between the cylinders to permit liquid from the upper cylinder to fall into the lower cylinder. During movement of the pistons in the opposite direction the cylinders are again pressure-isolated and the lower piston forces liquid from the lower cylinder through a spray outlet under high pressure.
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