Lesson 1/Learning Event 3
used to augment or supplement the crushing and screening efforts of construction battalions.
The washing and screening unit is used to wash, scrub, rinse and screen crushed stone. It also washes and
classifies sand. The auxiliary screening unit is a relatively simple three-deck screen. Its sole purpose is to
separate aggregate particles into specific size ranges.
Production Considerations. The washing and screening unit is capable of producing up to three size ranges of
graded aggregate and clean, processed sand. There is a wide variation in hourly production rates. This is
dependent to a considerable extent upon the particle shapes and even more upon the size of screen openings
installed. Rounded particles will process through screens faster than angular particles and large-sized screen
openings will process material faster than smaller ones. The rate of production of the auxiliary screening unit is
also determined by particle shape and size of screen openings.
This equipment is so highly versatile and is commonly used in so many different arrangements that no particular
employment concept could be termed typical. It can be used to reprocess materials existing in stockpiles, to
operate independently in gravel pit deposits, or in conjunction with the 75-tph Set No. 1 to increase production
rates and processing capabilities.
Function and Operation. The 225-tph plant is a very large, portable plant with tremendous processing and
production capabilities. It is designed to process quarry rock or gravel in either washing or dry operations. It is
issued on an as needed basis for large crushing and processing operations, and comes complete with the personnel
necessary to operate it. The 225-tph plant is composed of a primary unit, a first intermediate unit, a washing
plant, a second intermediate unit, and some other smaller items of equipment.