Page:Popular Science Monthly Volume 90.djvu/261

 Washing- River Water for Power Plants

Sifters on endless chains keep out the rubbish

��A POWER plant cannot use the water from the city mains since that would be too expensive. Instead it cleans the water of a river and pumps that up into the boilers and into the steam-condensers as it is needed. To-day, huge moving screens are used in the larger plants throughout the United States, but only a year or so ago, they were using stationary' screens placed in the supply-pipes which lead from the water. These were very unsatisfactory; for after heaw rain storms, the water would be filled with rubbish.

In the new form of filter this trouble is done away with. Here the screens are very much like platforms on a traveling-staircase. The water to be cleaned must first pass through the moving screen-sections before reach- ing the supply-pipes. When the rubbish which is carried along reaches the top of the filter, it turns around with it on a large sprocket-wheel and then meets a powerful spra^' coming from behind. It is thus whipped off the filter into a trough of run- ning water, and from thence it

At right: Diagram showing the details of the device and the course of the water over the screens

��is washed into the down-stream side of the river, out of the way.

These filters are built in single units which occupy a space six feet wide and about forty feet long. Where the water is let in from the river in channels more than six feet wide, a number of units, forming a battery of filters, must be placed side-by- side. In each unit, the screen-sections are placed close together on two endless steel chains driven by a small electric motor.

����The screen consists of two strands of chain carrying wire-covered frames

��Each unit is run by a small five-horsepower motor and is cap- able of cleaning sixty-nine million gallons of water per day

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