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Shipping Bin Model With Basket Valve Gates
 Instead of pairs of slide gates, some elevators use BASKET VALVES to select one of two ducts at a diversion point. A Basket valve is a simple mechanism in which a blocking plate hangs on a shaft which rotates to move the plate from one duct to the other. The VRML model to the right shows the Ship Gate and Return Gate replaced by a single Basket Valve. The controls are simpler, because only one motor needs to be started, stopped, and reversed. Only two limit switches are needed, one at the limit of valve travel in each direction, compared to four for the pair of slide gates. Also, only two indicators are needed, one for each limit switch. This model is also fully operational and correctly wired. By looking at the model from the side, you can see that the limit switches are not inside the duct. Instead, they are mounted on the outside of the front cover of the ductwork, which is transparent in this model.

Because of its simplicity, a basket valve is easy to wire correctly. In the model shown, each indicator is wired to the Normally Open (NO) contact of its limit switch, so it comes ON when its duct is CLOSED. When the Basket Valve is between the two ducts, grain can flow in both directions and both indicators are OFF. It would also be proper for each indicator to be wired to the Normally Closed (NC) contact of its limit switch, so it would come on as soon as its duct opens by just a crack. Then when the Basket Valve is in motion, both indicators would be ON.

As with a Slide Gate, the placement of the limit switches on a Basket Valve is critical. Each limit switch must stop the valve just as it seats over the entrance to a duct. Otherwise, the valve can leak grain into the wrong duct, or the motor could try to drive the valve through the wall of the duct.

This model also has a monitor screen which moves down to cover the indicator llights when you click on it. The icons on this monitor are identical to the icons for a pair of slide gates. This is the same practice followed in real elevators. The icons convey the same information for a basket valve as they do for slide gates (whether a duct is open or closed off), so no new software is written just to make the icon look like a basket valve.

 

NOTE: If the model does not appear below you do not have a VRML player installed.