Because of its simplicity, a basket valve is easy to wire correctly. In the model shown, each indicator is wired to the normally closed (NC) contact of its limit switch, so it comes ON as soon as its duct OPENS, even by just a crack. When the basket valve is between the two ducts, grain can flow in both directions and both indicators are ON. It would also be proper for each indicator to be wired to the normally open (NO) contact of its limit switch, so it would come on when its duct CLOSES. Then when the basket valve is in motion, both indicators would be OFF.
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.
A pair of independently-controlled slide gates can be made to block both outlets at the same time, stopping the flow of grain. A basket valve cannot do this. If an icon for a basket valve ever shows both outlets closed at the same time, either it has been wired incorrectly or the gate is not a basket valve.
The icon for this model is identical to the icon for a pair of slide gates. This is the same practice followed in real elevators. The icon conveys 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.
In some elevators, a pair of slide gates is geared so that when one slide opens, the other one closes. With this arrangement, only one motor is needed to drive both gates. Just as with a basket valve, only two limit switches are required: a fully-closed limit switch on the return duct and a fully-closed limit switch on the shipping duct.
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