| 摘要 |
<p>A plastic sewage holding tank (17) in a boat (10), associated with a toilet (14), includes a vent check valve assembly (40) for providing vacuum relief. By mounting the vent check valve (40) in the top of the tank (17), when the tank is being emptied by rapid pumpout implosion or other damage to the tank is prevented. The vent check valve assembly (40) may include a valve body surface (45) operatively connected to the tank (17) and having a plurality of openings (46,47) formed in it, and a flexible material diaphragm (60) covering the openings (46,47) adjacent the inside of the tank (17), and uncovering openings (46,47) to allow air flow through the openings (46,47) substantially only when a vacuum condition exists inside the tank (17). A plastic disk (61) biases the diaphragm (60) into its opening-covering position, but a partial vacuum of at least about 2-5 inches of water allows air to flow through the openings past the diaphragm (60). <IMAGE></p> |
