Factorio Forums

My setup. Chemical plant : set recipe check, read ingredients chek.
So the constant combinator sets up the recipe of the chemical plant, who in turn sends the ingredients to the requester chest and to the 4 pumps connected to the intake

The incoming pump is set as follow : Meaning, it will sets its filter to any requested liquid. In this case, if acid is requested, it will pump the acid, if anything else is requested it will pump nothing,

The outgoing pump is set like this ; Basically, if any recipe is set that does not need acid, the pump will enable and thus purge the Chemical plant's intakes from any acid.

It is the same setup for water, on the other side. As for the external pumps connected to the storage tanks, they just ensure that there is never more than 10k water/acid in the storage tanks to allow the purges. This is a pretty basic setup, nothing fancy.

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Here is the (very minor) bug :
I decide to make batteries :
Note that there is acid only on the right intake.

I switch to making explosives :
You'll see that now, there is acid on the left intake.
In this particular case this is easily solved by connecting the two intakes, because the chemical plant requests only one liquid.
But what if I want a third recipe, let's say sulfur :
Now, because there is two different liquid in the recipe, I can't connect the intakes together, right ? So I'm stuck with acid flowing were I don't want it to be.

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What I think is happening : when changing the recipe, the chemical plant "discharges" the leftover liquids stored where it can, in this case in both intakes. But once this happen, the intakes are not "connected" via the chemical plant anymore, thus, you cannot purge all acid in the intake using a pump on only one side.
There are multiple solutions to this problem. A simple solution can be this :

So I'm not looking for a fix.

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I just need to understand. Because here's the catch : this doesn't happen for every liquid. As an example, light oil never flows in the "other side", neither does water or petroleum. It ONLY seems to concern acid, in my particular case. This is just a strange behavior and I can't explain the inconsistencies.