| 摘要 |
The dispensing head (7) consists of an axially-moving pusher (26), forming a pumping chamber (22) with an intake (14) closed by an inlet valve (16) on a piston (12) which has at least one seal lip (12a, 12b) in contact with the inner walls of the chamber. The piston is able to move between upper and lower positions, first drawing in the product and then expelling it through a dispensing valve (40), while a spring (32) returns the piston to its upper position. The piston seal lips are made from a rigid or semi-rigid material, while its inlet valve (16) comprises a membrane of a supple material. The material used for the membrane is selected, for example, from the group of thermoplastic elastomers comprising propylene/ethylene copolymers, polyether blocamides, polyvinyls, ethylene propylene diene terpolymers (EPDM), sequenced styrene butadiene polymers (SBS), sequenced styrene ethylene butadiene polymers (SEBS-SIS), thermoplastic polyurethanes, or mixtures of polypropylene with SEBS-SIS, EPDM or SBS. The membrane can be made e.g. from natural or synthetic rubber, such as nitrile or polybutadiene rubber. The piston itself is made e.g. from polypropylene, high or low density polyethene, PVC, polyacetal, ethylene vinyl acetates or mixtures of these. |
