How’s Your Plumbing?
When I built the Semi auto machine, that has pretty much gave me all the code theory I need to build a full auto machine, the only real additions will be a few more relays and some solenoid valves for opening and closing valves, and powering pumps.
One Pump or Bust
I did build a prototype valve system just to see if the concept would work. I used 6mm tubes and valves and a small reversible (geared) pump.
If you follow the path which the chemicals would take, it makes sense. The dev tank would be on the other side of the pump (not connected in this picture) This system worked, but had 2 problems, both quite big. Firstly, 6mm tubing was too small for the volume of liquid that needed to be shifted in short periods of time, secondly the pump was too small, and big geared pumps are £££££.
When I shelved the project in 2019 due to other commitments I sold the valves (there quite expensive LPG gas valves, ideal for fuel shut off valves in classic cars). and kept the pump.
Two pumps are better than one
Now in late 2019 I sat down with some paper and started to think, if one fancy pump is expensive, why not try and use two with some extra pipework? Normal pumps are cheap, and to fix the other problem, why not upgrade to 8 or 10mm fittings?
After a few false starts, I’ve come to this point with a 2 pump design,
Well this version needs 7 valves instead of 6, and 2 pumps. That is a small price to pay for an overall much cheaper setup.
I’ve fitted two check-valves (one way) to the project. I think these are needed and cost pence so thought it would be easy to start this way.
It also means I can search for 10mm fittings and valves/pumps. I think if I can find an 8 litre a minute pump, this would balance speed and tube size.
You could for example drain a 500ml chemical in 10 seconds, based on tube size and pump. This is a rough guess. Far better than the 20 or so seconds for the other system, which would have affected process timings.