Keeping Wastewater Wells Clean – Relatively speaking
A few years ago, we found that operators in a few wastewater utilities in one state were visiting their lift stations regularly – some once a week, others once a month, to pump the station right down to the snore point of the pump. It was an important maintenance task because pumping the well down as far as possible was a great way to clean out as much of the build up as possible.
The operators here found that the result was more reliable operation of level devices, less pump blockages and less need for frequent visits from the cleaning crew.
That insight led to a simple well clean out function in the MT2PC, and then in a more advanced form in MultiSmart. The MT2PC version just allowed for a periodic pump down, every so many cycles for so many seconds. Customer feedback from the MT2PC feature was that some improvements could be made -which we couldn’t put into the MT2PC - but of course we did implement these improvements in MultiSmart.
How does it work?
The idea is that periodically, when the well level reaches the normal lead pump (duty pump) OFF point the pump down cycle is extended a little.
Optimize Station - MultiSmart
The MultiSmart feature allows the choice of how to initiate this extra pump down – after a set number of cycles (e.g. every 100 cycles), or on a timer. If you choose timers for the well clean out you might set Monday between 8am and 1pm. If it was a very slow moving well and the OFF point wasn’t reached within this time, the well cleanout wouldn’t happen. Normally of course the OFF point would be reached within this time window and so the cleanout would take place - but only once. The advantage of the timer over using number of cycles is that you can make sure it takes place when people are at work – in case there’s a problem.
Should we introduce “Stop on under-current”?
There was a third choice for the well clean out that we think is a good idea but it hasn’t gone into the product yet (as of writing this post) – run the pump on until under-current - i.e. until the pump starts to snore. In a way you can use this already, but you’ll get an under-current alarm!
If you think that this would be a useful feature for you – or you have any other comments about this feature or the practice of cleaning out wells – please comment (below)!
How is it setup?
From the Settings menu, on the first screen you see Station Optimization, select that and Optimize and you’ll find the well clean out function with all the parameters. You’ll find some other useful features there as well.
Disabling the low level alarm is managed from the level alarms in the advanced menu: Advanced – Pump control – Well – Well 01 -Level alarm -Low level – Well clean out disabled (check the box). You might have a low low level alarm as well, if you do you should do the same for that alarm.
Hi Steve,
The “Stop on under-current” would be a good idea, but it depends mainly on the configuration of the pump layouts. If a pump starts to snore, chances are likely the water level would be very low. This may cause air to be trapped in the vertical pipes and once normal cycles resumes, there is a high possibility of an airlock.
An alternative would be the ability to set a extended delay shut off delay every programmable preset cycles.
Another idea is to have a variable called “pump body” height (eg 0.6m). The controller would calculate the time taken for each point change in the multitrode probe. Lets say 30secs for every 0.3m on average for that cycle. So when the water level reaches the OFF point, the controller will run for another 60secs or less to cater for the 0.6m of water. A safety note to consider is that the pumps must have a cooling jacket if the water level is to be below 3/4 of the pump body.
Steve, I agree that under current will probably lead to air locking in many installations. We recommend that a cleaning cycle should stop when the level above the pump’s suction reaches 3X the suction diameter. Joe
Hi Kaewen and Joe, thanks to both of you for your comments. It sounds like we shouldn’t introduce that feature – and probably should include a note in our manual about the safety margin.
I like Kaewen’s proposal of using the calculated outflow rate to calculate the time to run on, so that it pumps a known distance. Great idea.
One of the concepts behind the sump clean-out feature was to pump out the grease that normally floats on top of the liquid; and to do this, the level would have to get down to pump snore level. I guess the customer will have to decide if they want to avoid the floating grease bricks or avoid snoring the pumps.
Hey – great article. Stumbled upon it by accident but I’m glad I did. Will be back again daily. Cheers.
@Kaewen Tan
Re the undercurrent snore detection, if a customer does not want to snore the pumps due to the issues mentioned, they need to set the parameters to avoid this. However, if undercurrent detection is enabled, the clean-out cycle will be stopped as soon as a snore is detected. Without it, bad programming of parameters, or changes in well conditions (inflow) will lead to an extended snore anyway, likely resulting in a undercurrent fault after snoring for much longer. The other possibility is that a snore will produce a current draw that will raise and fall as air and then water are pumped, and not drop the current for long enough for a full undercurrent fault, so the snore will continue as long as the delay is set.