| 摘要 |
<p>This invention relates to an improved air driven pump for pumping products such as beverage syrups. Two opposed pistons are mounted on a common piston shaft for reciprocal movement within a housing. Cavities corresponding to the pistons are alternately vented and pressurized to intake the product into a pair of cylinders and to drive the pistons to pump the product. A spool valve stem extends into the cavity being vented so that the piston performing an intake stroke moves the valve stem into the other cavity. A pair of axial passages and corresponding side openings in the valve stem provide fluid flow paths for venting and pressurizing the cavities. A valve body biased toward the cavity being vented includes a vent passage for alternately venting the cavities through the side inlets. While one cavity vents, pressurized fluid flows into the other cavity through the corresponding side inlet and axial passage. The valve body moves with the valve stem until the biasing spring is in an unstable over center position, where the bias reverses to urge the valve body toward the other cavity.</p> |
