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State of California, Department of Transportation - page 32 / 52





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interlock, shall automatically shut the plant down when less than 70 percent of the target depth is detected. A time delay of 10 to 15 seconds is allowed between sensing less than 70 percent aggregate flow and plant shutdown. This delay is adjustable and is usually set during the initial California Test 109 and rechecked semi-annually. The time delay interval should be checked regularly by the AC plant inspector. Often during a bin clean

out, the device is wired up and out of the way to facilitate the process. If the device stays in the wired-up position, the controller will never detect a low

This “No-Flow” device is attached to the tail pulley and detects movement. No movement, and the plant is automatically shut down.

flow condition, even though it may be occurring on a frequent basis.

Caltrans also requires a device, located either in the stream of aggregate beyond the feeder belt or where it will monitor movement of the belt by detecting revolutions of the tail pulley. The device, commonly referred to as a no-flow interlock, must stop the plant automatically and immediately when there is no flow. No time delay is allowed by Caltrans specifications.

From here the collection belt, also referred to as a gathering conveyor, carries combined aggregates away from the cold feeds to the weighbelt.

In most continuous mixing AC plants, a scalping screen is located between the collection

belt and weighbelt.

This vibrating

screen is designed to remove any oversized rock that was inadvertently introduced to the aggregates during processing and


Weighbelts All aggregate weighbelts are required to have concrete footing under-supports for each scale bearing point, per Section 9-1.01,

of the Caltrans Specifications. This conveyor incorporates known as a weighbridge.



Standard type of a device When the (moisture

This photo shows the collection belt, then a scalping screen and then the weighbelt. Notice the shielding at the weighbridge (arrow).

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