 A reservoir control circuit is very similar looking to a sump control circuit, but there's some big glaring differences in the fact that a sump circuit is meant to collect water and then dump it out or drain it out somewhere else as opposed to a reservoir which is supposed to be a full tank that empties and then needs to be filled at the end. So what will happen is a sump circuit will utilize normally open float switches and a reservoir control circuit will utilize normally closed float switches. So here we have a typical reservoir circuit. We have the reservoir drawn off to the side here. These floats I'll show you are associated with these floats that are in the control circuit. I have a three position selector switch hand off auto. So we're going to focus on the auto position. In hand the motor will pump or the motor starter will engage and then start at the pump which will fill the tank all the way up by hand. But if you're not watching it get overflow and you got water liquid everywhere. Now if we go to the automatic however we've got these floats that control the whole operation. So we're going to walk through to see what happens here. So let's say that this reservoir is being used, they're watering their lawn. So the pumps out, watering the lawn, we're going to start seeing the level drop in the reservoir and when that happens we're going to watch what happens to these floats in the control circuit here. Now we've got it emptying past our high level float and you'll see that our normally closed is now dropped down into the normally closed position where it's normally would be without any sort of liquid in there and it stays closed. However we don't start pumping water back into the reservoir quite yet because if we did that then we would end up just draining the tank to about halfway and then filling up and draining halfway and filling up. What we want to do is be more efficient than that. We want to drain this tank all the way down to the bottom and then we'll fill it up. So we'll wait until the low level switch engages and we'll see what happens. Now here we have the level has dropped all the way to the bottom of the tank which means that the high level switch has dropped, the low level switch has dropped and now the motor starter has engaged. And so we have some sort of pumping water back into the reservoir. So we're going to start seeing the level rise up and as the level rises up these floats will go back up into their position. So these normally closed float switches will open up and we'll see what happens next. Now our low level switch is opened but again we don't want that to just stop the circuit. We want to keep going until the high level switch is empty or is opened so we can see that we get to the top of the tank. So we've got this holding circuit in here. So an M is energized, our starter is energized. This is a holding contact that is associated with M. So it will stay closed so it holds it in. So it'll still allow that to pump liquid back into the reservoir and continue to fill the tank. Now what'll happen is we'll see that these will rise up and the water level rise up and we'll see our high level float open up as well. And let's take a look to see what happens when that occurs. Once that high level float has gone up the level of the tank has raised. So it's lifted that float tank up. It has opened this circuit which was already fine because we had that holding circuit but now it's killed the whole circuit because nothing can get through this normally closed which is now open float switch because it's being held open in the tank. Then M will de-energize, the holding contacts will de-energize and everything will stay as it was. Just waiting again for the levels to drop down and continue into the cycle. And that is how a reservoir control circuit works. One last thing to make mention of is the question of whether or not this is a low voltage protection circuit or a low voltage release circuit. When we're dealing with sumps and reservoirs, they are both considered low voltage release. Meaning that if this switch was down closed as float switch and this switch was closed in the closed position and this was energized and running, then the power goes out. This would de-energize. But once power is restored to the circuit, if these switches, these float switches are both still in the normally closed position, this will start up instantly and away we go we get the circuit running again. As opposed to a low voltage protection circuit in which we would have to re-engage the circuit and press like a start button to get the whole circuit up and running again. It's often beneficial to have these reservoir and sump circuits in a low voltage release situation. Because you don't want to have somebody running around all over the site or the plant trying to restart sumps and reservoirs or else you end up with things overflowing or emptying out and that would not always be beneficial. So again, sump circuits and reservoir circuits are low voltage release.