Schnieder

First of all, I am an apprentice working with the power house in a mining company.

PLC is new to me and I think we are using the PLC type Schnieder (not really sure of the version) to operate pumps.

When set to auto mode the pumps dont work but when set on manual mode the pumps work, what is the cause of this?

well we would need alot more information than you have provided.

but if i had to guess,,,
when in manual mode, id assume that is a direct on off in the program. but auto means something is controlling it. therefor i would guess that that is where your problem is...

Typically, "Auto" mode means that there is a sensor feedback signal that controls the device (pumps) in this case. For pump control, the most likely would be pressure switches or level switches. If a pressure switch failed, then the auto mode likely would not turn on the pump, but the Manual mode (bypassing the pressure switch) would still work. The Auto Mode could also include other devices, such as interlock switches with other equipment that has to run before the pumps will run in Auto.

In some cases, where there is PLC control, Manual Mode may also bypass the PLC so that the equipment can be run if the PLC fails. I would guess that for mining dewatering pumps, a PLC Manual bypass would be a desirable feature.

I would start troubleshooting by searching for a wiring schematic drawing of the pump control system. A well-made schematic will show the Auto and Manual modes, and the control logic difference between the two modes.