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The Basics of a Duplex System

Building redundancy into a mechanical system via a duplex pump system is cost effective and efficient for a wide range of applications. In Wisconsin, duplex pump systems are required in commercial building where there are three or more water closets or when more than 20 DFUS are draining into the sump basin. Duplex systems can also be used for drainage and dewatering.

As its name suggests, a duplex system means there are two pumps to handle the daily flow rates. The heart of the duplex system is the alternating control panel that, through the activation of sensor float control switches, automatically alternates between the two pumps. This not only equalizes pump wear but provides override control should either pump fail or if the second pump is needed to handle a heavy inflow.

The alternating control panel is operated by typically three sensor float control switches: stop float, lead float, and lag/alarm float. There are some systems that do use four floats – incorporating a redundant alarm or off function.

The stop float is the float that turns off whichever pump was called on to run. The lead float is the float that runs on whichever pump happens to be called for at that time. The third float is the lag/alarm float. If the liquid is to reach this float, the lag pump will turn on and the alarm will sound, warning there is a problem with the system.

Note that an alarm device must also be installed on a separate electrical circuit, separate from the circuits feeding the pumps. If you are using one breaker for the incoming pump power for both pumps, it needs to be sized for the possibility of both pumps running at the same time. It is highly recommended to have separate circuits for both pumps and the alarm, totaling three circuits.

Jim Murray Inc. is able to assist you with finding the best duplex system for your application, including ones that may require no tethered floats. For more information, contact us at 800-234-5490 or sales@jimmurrayinc.com.