Generally I don't do a lot of offering unsolicited advice, but because of past, and more recent experiences, I believe it's appropriate. Over the past several months, I have fielded MANY phone calls and emails from individuals seeking my help/advice in finding/fixing problems with PID controlled forges they have built. I have become somewhat frustrated, because these type of forges simply are not capable of working as most anticipate they should, and when I try to tell individuals that, they get defensive, and several have even "gone off" on me. I don't want to be this way....but I am nearly at the point where I want to simply refuse to help anyone with these PID controlled forges.
For those who don't know what a PID Controlled for is..... essentially its propane forge, which uses a solenoid valve, with a PID Controller to turn that solenoid valve on/off. The idea behind it is to be able to set or adjust the controller to make the forge maintain a given temp. While this might seem a great idea in theory, the results are often very different in practical application. In short, an individual's expectations generally far exceed the capabilities of this type of forge. Were it not for the variables inherently involved with the uses of a forge, these type of devices MIGHT be viable, but for the most part they are simply a "money pit", that create more problems then they solve.
Nearly every request for help I've received begins with "As long as I don't put anything in the forge, it holds the set temp, but when I put steel into the forge the temp overshoots or undershoots the set temp way too much." Therein lies the problem with PID Controlled forges... the variable of mass that a person introduces (in the form of a bar/billet of steel), and how much/often that mass is removed, reinserted simply cannot be anticipated by the controls, causing the unwanted temp fluctuations. It's actually very simple, but its very difficult for most to understand.
OK, having said that, the next issue is the number/amount of parts this type of forge requires...... way more parts, and way more complicated then a simply designed, single burner forge. To put it bluntly, when it comes to a propane forge, the more you overtake the plumbing....the easier it is to stop up the drain. There's just more to go wrong, more parts to connect (and possibly connect wrong), which generally creates a overly complicated device, which just opens the door for more and continuing issues/problems.
I have to believe that many seek to build these types of forges in hopes of dodging the learning curve when it comes to forging, and even though I do my best to explain to those who've sought my help/advice, that there simply isn't a "magic bullet" that will eliminate the learning curve.....it often just bounces off, and the individual struggles along, trying to chase a unicorn that they are never going to find.
My advice is this..... before you spend the money and time to build a PID controlled forge, think hard about it, and temper your expectations to a realistic level. It MIGHT be helpful in a limited number of scenarios in your shop, but it WILL NOT be all you anticipate/expect. There is a reason that experienced Bladesmiths build/use forges that are of simple designs..... it's because they work, and because those simple designs keep on working, without presenting constant problems/issues. Do yourself a favor.... if you're thinking of building yourself a propane forge, steer clear of overly complicated designs, and ALWAYS, when it comes to building a propane forge....stick to the "KISS" principle.