Lift Station Float Elevations

[j9777]

I am working on a Master Lift Station design and wish to know if there are minimum design standards for the lift station float elevations - alarm on, lag pump, lead pump, pumps off, etc. Can anyone recommend a design reference also. Thanks in advance for the information.

 

[aussiemike]

The cut out float should be set a distance above the floor in accordance with the minimum pump submergence provided by the pump supplier.

The lead pump should be set above cut out to give an active volume so you don't exceed your pump starts.

The lag pump (depending on your philosophy) can be set a minimum of 150mm above the lead start (so long as this gives the lead pump time to ramp up before it triggers the lag pump unnecessarily).

I have assumed your PS is not under variable speed control. Mail me back if you need more help.

Cheers
Aussie Mike

 

[semo]

For smaller lift stations.

I set the stop float at an elevation above the pumps as recommended by the pump manufacturer. They will want a minimum submergence.

The lead start float should provide a minimum volume as dictated by the following equation.

Vmin = Tmin X Q / 4

The Tmin is 6 minutes which is the cycle time. It provides for 10 starts per hour.

Q is the pump capacity in GPM.

I don't know of any hard fast rule for the lag pump volume. I typically use approximately 50% of the Vmin.

I typically then place the alarm float 3"-6" above the lag pump on which should be at or about the lowest inlet flowline.

 

[j9777]

Thank you both for the valuable information. This lift station will actually be a Master Lift Station, with peak flows of about 1100 gpm. Your input is appreciated.