The closed construction airlock valve provides positive seal under hoppers, cyclones and dust collectors. Because this dust-discharge valve requires no controls, lubrication or power source, it is both energy saving and maintenance-free — allowing it to operate for about one-sixth the cost of a rotary airlock valve used for discharged dust or abrasive materials, according to the manufacturer. The duckbill valve design allows free-flowing continuous discharge, automatically adjusting to the desired vacuum. To see an animated demonstration of how a duckbill airlock valve works go to www.aerodyneus.com/013. The duckbill valve is offered in carbon or stainless steel construction. Sleeves for this airlock valve are available in neoprene, viton, and white nitrile, making it suitable for general use, high-temperature or food grade applications. The airlock valve has a durable enclosure making it useful in controlling dust in windy outdoor applications or in applications where the valve is not positioned close to the collection container. The enclosure has an easily removable access door.