Anyone familiar with alternating sump pump control?

Sure, extremely simple with common alternating relays and built in with the float assemblies. What sort of questions???
http://www.tesensors.com/products/nema-square-d-pressure-switches (Square D 9038 Series)
Here's just one mechanical example: A long rod from the float runs through the actuator lever with a collar above and below. The bottom collar is used to set the lead pump start height. The pump drains the sump to the height set by the upper collar. The switch will start the 2nd (new lead) pump the next time the water rises. Should the lead pump not be able to keep up, perhaps a check valve on the non-running pump has failed, the lever will rise to a second stage where both sets of contacts close. This causes both pumps to run until the upper collar switches them off. They don't alternate when this ocurrs.

For relay methods, duplexers and triplexers, are other names for the alternating devices. Here's one common brand.
http://www.marshbellofram.com/diversified-electronics/types/pump-level-controls/
Hope this helped!
Joe

I have a drawing for one I worked on in my truck. I can share it but it sucks a little because it only alternates when the power goes out and a bad stop float prevents the pumps from starting even when it hits the high level.

This is what I was looking for. Four high rises we work in have them. 2) 1/4HP motors 115V. 3 floats. Primary, lag and alarm. However when checking with meter, the floats are working in tandem. The pumps alternate but do not run simultaneously.

Coincidentaly was called there this morning. Another one of the four has two 208v motors and a different control box. Three float system. Lead float closes one of two contactors. Pump runs until water level low enough to close stop float. 3rd float is alarm. Fuse was blown so they called because they were not working. Existing fuse was 15a and should of been 20. I do not know what motors were in before. They do stuff over there all the time in house and when things don't work they call us.

How could both these motors run simultaneously with only a start and stop float?

A three float system I worked on 'back when':

Float 1: Activate pump 'on' at a set level
Float 2: Activates second pump at a higher set level
Float 3: Activates high level alarm.

System was two, 3 phase sewage lift pumps at a strip mall.

Controller had two starters, and an alternating 11 pin relay. (From Grainger)

That's about all the details I remember.

I've worked on many types of pump control schemes from bubblers with pressure transducers, to metal probes with Gems sensors, to Healy-Ruffs with dial indicators, cables, pulleys, cams, and Hg switches. The 9038 mechanical alternator I described, starts and stops 1 or 2 pumps with only 1 float and a rod with 2 collars. They can even control single phase pumps directly although we don't use them that way. They can also be ordered to include the alarm option but we always use a separate float or sensor so we won't have all of our eggs in one basket.
I'll bet that I've seen the system(s) that you're dealing with but you would have to provide more of a description.

Just to make sure that we are on the same page, this is how I check the sump pumps and 63W alarm at our substations.
1.) Make sure there is enough water in the sump to keep the pumps from running dry.
2.) Lift the alternator lever to the 1st click to make sure Pump 1 starts and runs for a few seconds, before lowering the lever to stop the pump.
3.) Repeat step 2 to make sure Pump 2 starts.
4.) Lift lever to 2nd click and verify that Pump 1 also starts, and then lower lever to stop both pumps.
5.) Raise lever to 1st click again to verify that Pump 2 starts. (No alternation because both pumps ran.)
6.) Allow the pump to run until the upper collar on the float rod turns it off.
7.) Open both pump disconnects and use a hose to fill the sump until the 63W Alarm annunciation. Verify that this occurs at a higher level than the second stage of the alternator switch. Our alarm is actually a pressure switch instead of a float.
8.) Stop filling the sump and close both pump disconnects to restore normal operation. Reset the Annunciator.
If the above steps check out OK, I'm confident that the pump scheme is working as designed.
Joe

I think we need a refresher; some of the above information is incomplete.

Floats on rods? How quaint. The most common arrangement uses simple floats on cords, tied off to a pipe.

If there's but one pump, and one float, the float has a 'piggyback' plug, and your delay between 'on' and 'off' is built into the float.

The delay prevents short-cycling of the pump. Typically, the float will be pointing noticeably 'up' before the contacts inside close, and pointing noticeable 'down' before the contacts open again. This gives you perhaps a 4" difference between the 'on' and 'off' water levels.

For duplex pumps, you have a single circuit supplying the control panel. The control panel, in turn, feeds the pumps.

Your lowest float doesn't seem, at first glance, to do anything. Yet, if it doesn't close, neither pump will work. It serves to shut everything 'off' after the sump has been pumped down.

The next float turns on the first pump. An alternating relay in the panel will make the pumps take turns being 'lead' pump.

The third float - usually also the top float- will turn on the second pump and sound the alarm.

If there's a fourth float, it's the top float, and it only sounds the alarm. In this set-up, the third float only operates the second pump.

Now ... commercial plug time ... I've seen a variety of pump panels. One place seemed good, until I called them for a replacement part, and only silliness followed.

A surprising number of the panels I've seen, under various names, have come from SJE-Rhombus. You can buy direct, and their customer service is top-notch.

I agree corded float switches are the norm, I have 3 in my aerator tank but a well designed tethered float in a rod is a lot more durable and precise.

That is what they are Reno, cord floats. There is no schematic or info on control panel in first building. I think what you are saying makes sense. I checked voltage at T strip and two floats seem to work in tandem. So if I am interpreting you correctly, 1st float closes than second float starts pump, and they alternate with the alt relay. That seems correct. Third float should turn on alarm and make both pumps run simultaneously? Okay, I did not check third float because I was told it was for alarm and the alarm is broken. This sump is very large so I never was able to fill up with hose. Would of taken hours and also would have had to pull up second float to allow water level to get up high enough. I guess I could of lowered third float in hindsight to test. The head of maint. there ordered another panel (Dayton). When I go to install I am going to check on what you are saying. It makes sense. Four buildings and all sump panels are different. Also people who shouldn't be touching elec keep messing with these things. The co. who changed pumps in one building, installed two brand new 120v pumps, and hooked one up with both legs on the contactor(208) It ran, but was drawing 37amps!!! 1/4HP. Head of maint who keeps telling me he is a 'master electrician' swore up and down they had two 240v pumps, until I pulled them and showed him they were 115 1/4hp.

You've got it.

Fill the sump? Don't bother- just have enough water to cover the motors, as they use that for cooling.

You can use a hooked stick to manually raise the floats.

The Dayton panel is made by SJE-Rhombus. The third float will both sound the alarm and start the second pump. The panel has an alarm silence switch that will quiet the horn, but the light will continue to flash.