I get a lot questions on the basic functions of duplex wastewater systems and, in particular, the duplex panels used in these systems. The basics are really quite simple
SEQUENCE OF OPERATION
Each of the two pumps should be sized to meet the anticipated peak flow on their own.
The panel will start pump number 1 when the stop and lead float switches are both engaged.
Once the pump has started it will continue to run until the the stop float disengages.
At the end of the stop/start cycle, the panel will alternate the two pumps and promote the lag pump into the lead position.
On the next cycle pump number 2 becomes becomes the lead pump
Should the liquid level continue to rise after the stop and lead floats are engaged and rises to engage the lag float, the pump being held in reserve will start. ( in a three float system the alarm will also be activated.)
If the lag pump is activated because the lead pump cannot keep up with the flow rate, both pumps can operate at the same time.
The following points answer the most frequently asked questions about duplex panels.:
Single phase panels require two electrical feeds: one to supply the pumps ( voltage to match the pumps) and a second 120v feed to power the control/alarm circuit. (If power is lost to the pump circuit, there will still be an alarm).
Three phase panels use a single power feed and an internal tranformer to supply 120v to the control circuit. A separate 120v feed can be brought to a three phase panel to be used instead of the power supplied by the internal transformer.
The NEC requires that a separate, lockable disconnect be installed in front of the panel. This eliminates the need for an internal power disconnect in the panel.
Three float vs. four float systems: the orginal duplex alternating panels used mechanical alternation and required 4 floats to keep the system in sync. Todays solid state alternators do not require 4 floats to operate properly.
The three float system uses a jumper to connect the alarm to the float sequence. The high water alarm will be activated whenever the lag pump float is activated. This will happen if the lead pump for that cycle fails or if there is an unusual amout of inflow into the basin that overwhelms the lead pump. Operators should be made aware of either situation.
A four float system should be used in applications where both pumps may run at the same time. This would result in a false alarm if a three float system is being used.
In any system, the float switches do not interact directly with the pumps nor are they assigned in any way to any of the floats. The floats signal the panel to activate or stop the pumps from running.
Do you have any questions about float operated duplex panels.? Any comments on the above?
Use the form on the website or contact me directly at: gwilliams@geofwilliams.com. We'll try to answer them in a future post.
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