The Delta Controls Model 717A is very similar to the Model 716 displacer switch, which has only 2 alarm points. The major difference is that the stroking distance has been increased and a third switching station and displacer have been added.

A precise on/off action occurs in the appropriate switch station when the liquid level surface passes the elevation of the related displacer element.

The Delta Controls Model 717A is commonly used to control two pumps acting to empty a sump. Each of the two top displacers starts a pump; the lower displacer operates a DPDT switch, which acts to stop both pumps at the same place. Latch/unlatch pump starters are normally used in this arrangement.

 

 

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MODEL 717D - 3 DISPLACER, 2 STATION DIFFERENTIAL CONTROL

The Model 717D utilizes a mechanism and displacer similar to the Model 717A three-point alarm. The difference is that an adjustable differential device has been added, and only two switch stations are utilized

The lower switch station is activated when the liquid surface covers the middle displacer, and stays activated until the liquid level falls below the bottom displacer.

A typical application is to control a single pump with a high or low level alarm.