waste water treatment

[Charbel]

Dear,

I am using a low level switch in waste water tank interlocked with pump, this level will stop the pump in case of low level in the tank, specially in manual mode.

will this level switch break overtime due to contact with the sewage? what is your experience in this? if proper material is used, i believe this will be ok... what do u think?

There is an alternative for protecting the pump in case of low level in manual mode, stop the pump based on current supervising... what do you think? will it be too late to wait for the current to rise in order to stop the pump?

Which option, you think is most suitable?

thanks!

charbel

 

[Tom Jenkins]

Float switches can be very reliable. There are a great many available in stainless steel and non-metallic construction that are specifically designed for sewage pump station wet wells. You can find some examples here:

http://search.usabluebook.com/search?keywords=float+switches

I suggest you talk to your pump supplier - they probably have a good deal of experience. One additional caution: raw sewage wet wells tend to generate methane from the action of anaerobic bacteria. Codes often require intrinsic safety barriers between the float switch and the control components:

http://www.usabluebook.com/p-271852-intrinsically-safe-relay-latching-24vacvdc.aspx

There is nothing wrong with using current monitoring as a secondary protection mode if you distrust the float switch.

 

[John Soltesz]

Another way to protect a pump is to monitor the motor load. This would be in addition to a level switch. It would also give indication of a broke shaft coupling.
Here is one company we have used many times.
http://www.loadcontrols.com/application_notes/application_notes.html