| 摘要 |
<p>An apparatus for dispensing a dose of fluid comprises a dispensing vessel 1 having a dispensing outlet, a piston 4 and a vessel wall defining a cylinder 1a in which the piston is moved under pressure between a first and second position. The apparatus includes a bypass passage 8 extending through the piston and has a bypass valve (4b, fig 5) opened by a valve actuating plunger 9 within the piston to open the valve when the plunger abuts a shoulder at or near the second position in the vessel. First and second sides of the piston may define with the cylindrical wall respective first and second chambers in the vessel. A second piston having a respective second bypass passage with bypass valve and actuating plunger may be provided (fig 9). The apparatus may be a syringe or mastic gun and may be used in applications such as dosing central heating systems with an inhibitor, medical systems and automotive systems. The shoulder may be annular, such as a ring connected to the cylindrical wall by frangible connections that break when sufficient force is applied by the piston. The apparatus may be used for mixing and dispensing multiple bodies of liquid.</p> |
