Sump operation question

[Aleman]

We have a grease intercept where I work. This is a series of cascading pits and a sump at the end that is pumped to the city.
It has 2 pumps and 3 float switches. The original controller died, a mini Scheider PLC/smart relay. I put an Eaton controller in it that has
the same footprint. I set it up so the middle float starts the pump and the bottom switch will turn it off. The high float is an alarm. The
2nd pump will kick in if it doesn't make the bottom within a set time or if it trips an overload.

Which is one way to do it. Or...could just use it same as having the floats directly switch the contactors. Where the bottom float will run
the motor till it it switches off. The middle would start the 2nd pump, and the high is the alarm.

Not sure which would be better, but 1st method will be less short cycling. I could add another float but it's a nasty job. Not sure about
how these are set up with 4 floats but the original had that option.

I figure some of you guys have dealt with sumps so why not ask for input. I can do it either way but I am wondering how these are
usually set up.

 

[ActionDave]

Go with plan A.

All the lift stations in my fair city are set up much like your description. They do have a fourth float which is the alarm. Third is the high wet well. It starts the second pump if needed. Second is the start float and first/lowest is the off float.

Do you have an alternator? That and an hour meter on each pump is handy for spotting a problem with one of the pumps early.

 

[StarCat]

Duplex Lift Stations

Duplex Lift Stations

Dual pump stations I have worked on typically use "4 " floats, the 3rd one up bringing on your lag pump for extra volume and also having an alternator in the circuit.

 

[Barbqranch]

I would also go with plan A, but if you can, in the PLC, set it so the top float triggers the alarm but also starts the second pump. Could even have a short delay on the alarm. Part of the design process is what is the maximum flow in as well as the pump capacity and available tank capacity.

 

[Aleman]

All good ideas thanks! I was planning on alternating the pumps, probably get it this week. I will stick with the 1st option as this seems more
common. The orig had a 4th float option and if the 4th wasn't used, that input was jumped to the 3rd switch. I will set the top switch to start
the 2nd pump if not already on. The design I am stuck with and I am not sure of capacity at peak hours. It has always worked with 2 pumps ok
until the controller went out. The new pumps are slightly larger so it should be all good.