lift station

[Saffa]

A completely independent backup control system is well worth the small additional cost. For our setup it works out to about another 5% increase in new panel cost. Well worth it - if we lose communications with a site for more than an hour, an operator goes and takes a look. If the station starts on float then he can go back to bed if it's the middle of the night. No need to call the sparkies out in the middle of the night at time and a half to try diagnose whether it's a radio or the PLC, then get me out of bed to send the new program over, find they haven't set the radio up right, have to drive to site in my Spongebob onesie pyjamas... you get the idea.

You'll never make it 100% perfect but in my experience the things that die most often are: DC Power supplies, level sensors, PLCs / RTUs and comms equipment. Not every second day mind you, but when you have several hundred stations the likelihood of a failure increases. And for the love of god put your backup controls power supply on a separate circuit breaker.

And when you avoid Mrs Jones having sewage flowing down her driveway, in her front door and over her new Persian rug, and "she's friends with the Mayor, and she'll have you fired just you wait and see", it'll be well worth the extra money!

 

[Tom Jenkins]

If you have a level transmitter you want to have float switches for alarming and to cut off all pumps (low-low) and start all pumps (high-high)

Two pumps are common for small stations. For large stations three or more are used, sized to accommodate the large difference between minimum and maximum daily flow rates.

Level transmitters are used with variable speed pumping to maintain constant wet well level. This is often justified by energy savings, but it depends on whether the pump head is mostly friction or static lift. The type of electric bill makes a difference too.