In this Condenser article, we review the position indication switch and how it works. Learn why you might need a DPI switch with the Newsstand.
Is the damper open or closed? This may seem like an odd question to ask, but it will be important to know the answer during a system failure. Control dampers will often join two sections of duct, which makes it difficult to see the damper's blades. You will need to disconnect the damper from the duct to perform a simple visual inspection, if a failure occurs. In other words, you would have to uninstall the damper. That's a lot of work, especially considering the number of control dampers in your HVAC system.
Pictured: A position indication switch with a blade position rod.
During a system failure, you need to diagnose the issue and resolve it as quickly as possible. Most actuators will have a series of lights that indicate its current position. There can be two lights, for full open and full closed, or multiple lights for modulating dampers. These lights are useful, but they will only indicate the actuator's current position. If the damper has failed, these lights won't help you.
If everything is working correctly, then the actuator position will be the same as the position of the damper's blades. If the blade axle is stripped or damaged, it may no longer rotate with the actuator. This means that the control damper could remain closed, even if the actuator reads that it's fully open. This is where position indication switches come in.
A position indication switch, also called an auxiliary switch, is a secondary device that signals the position of the damper’s blades. The switch will be tied to the axle of the damper’s driving blade by default, like the integrated switch in an actuator. It can also be configured to test the axle and the blade. A metal rod is connected to the switch and propped against the closed blades. The rod will only move when the damper blade opens. It will return to its original position when the blade closes. This standalone option is considered the most accurate way of determining blade position, since the switch will be checking the actual position of the blade.
In this image, we demonstrate how a position indication switch can be tied to the blade axle and the blade itself. If the axle moves, but the rod stays in place, then the blades aren't opening when the actuator moves.
Manufacturers will often refer to these devices as “DPI” switches, or dual position indication switches. Most switches are designed to signal two positions: full open and full closed. Certain switches can signal for multiple blade angles. These switch types are used in conjunction with modulating actuators.
You have options when it comes to troubleshooting your control dampers. Consider adding some peace of mind to your control dampers with a position indication switch. Track your dampers and know whether they are open or closed.
For more on control dampers, check out these Newsstand articles:
Have you ever experienced a damper failure where you couldn't tell the damper's blade position? Do you use DPI switches with your control dampers? Share your experiences in the Comments section below. We want to hear from you!
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