Here's the complex bend that will connect the coil to the OPV. It has to be this shape because it needs to evade the steam pipe that comes down. Due to my steam pipe mod, I couldn't go around the outside (no room) so I had to go on the inside. You'll see in the next few pictures.
It wasn't as easy as 1-2-3, but it's nothing you couldn't do inside a weekend. I had been thinking and planning how to do this for months before I did it (today). It took me a full day, neglecting work as it were. :D
I've tested it and there were no leaks at all.
It didn't work the first time I plugged it in and started the pump... because I forgot to connect the tube at the bottom of the pump... duh.
After that... it all seems to work fine. I have not pulled any shots yet, since I'm still at work... closing down for the day.
I think Super_Pasty said he lost a bunch of pressure with this mod. This is probably because he didn't install all hard-line. I messed up my OPV adjustment because I thought I was low in pressure, too... but it was because there was no water coming into the pump, so I have to go home and calibrate my OPV again. Joy. I already disassembled my pressure gauge. Now to go find the pieces.
And that's a wrap.
Oh, I also have to recalibrate my PIDuino. I don't think it needs to be so aggressive after this mod.
I looked at passive preheat also. It looks like you have about 2.65*3.14*11 or 91.5" or 7.62' of copper pipe. OP said 7 ml/ft measured, up to 9 ml/ft calculated depending on ID or OD tubing. At any rate not a large volume of water to heat. At 9 bar the pump puts out about 260 ml/minute or about 105 ml/25 seconds. You get part of that in the boiler, shot volume replacement, and the remainder back through the OPV to the tank. You should flush the tubing with the first shot. It will be very interesting to see if it helps. There are other OPVs that could be put in line before the copper tubing and return cold water to the tank before it flushes the tubing. I doubt that a second shot in say 1 - 2 minutes will be significantly preheated, but that would be easily seen by a thermocouple on the copper line, or in the system, to measure.
You can do most of that stability with electronics. PID can stabilize intrashot reasonably well with alarm functions, so I am sure that you can do so with Arduino probably better. I tried to keep it simple so that others could do it as a PID install without learning a foreign language, Arduinoese :) Much of that is covered in the first post in the thread below including OPV possibilities. It would be easy enough to just leave the Gaggia OPV put back to 11 - 12 bar and then put an inline OPV before the copper tubing at 9 bar.
> Oh, I also have to recalibrate my PIDuino. I don't think it needs to be so aggressive after this mod.
Math says that the Gaggia has more than enough heater power to heat incoming water on the fly, even with no preheat. Just using the existing heater seems like an easier approach with the only question in my mind is if it can be controlled well/fast enough to keep the output temperature steady. Ie, open loop, power vs time table driven heat control during brew vs closed loop PID.
In other words, if you are running an Arduino and changing the programming anyway, is passive preheat (or a thermoblock) worth doing?
I did not want to change this thread that Daduck748 kept intact about passive heat. AndyPanda essentially did similar to what you suggest on PID thread above. He did it manually. He basically can keep pulling shots. The difficulty comes when your stop for 30 seconds or 1 minute to reload. You reach a balance of incoming and outgoing heat and then shut off the machine off to reload and then have to find the temperature again. Yes the heaters can supply more than enough for heat as there on less than 50% of the time using PID control with brew and not pre-heating incoming. If you want to discuss that, perhaps on a thread more appropriate, or a new one.
Easy enough to think outside the box, more difficult to implement in a cost effective way on an "inexpensive" machine.
I will answer Jonr's question in a way to keep the theead on topic.
I was skeptical when I first heard about this mod, but I've bad about a year to think about it before doing it.
With my PIDuino imementation, I've been able to keep idle temps within 1F of my target temp. However, I've had it set to a little more aggressive settings the last few months, just to accomodate unforseen circumstances and I've been OK with a small waiting period for the temps to stabilize. I use the closed-loop system when maintaning temps, then switch to a semi-open loop mode after the brew sequence starts, which means even though I switch off the PID function, I am still monitoring temps and adjusting as needed. I'm still seeing a 5F drop from start temp and end my shot at +5F at the end. Although this stays inside the 'standard' shot temp range, I'm looking to close that pull window.
This mod performed better than I expected. Keep in mind that it is more difficult to maintain temps (yet much more accurate) with an internal sensor, but with this pre-heater mod, I've been seeing a -1F drop and a +1F raise at the end.
I have not done back-to-back shots yet, but I will and let everyone know how it goes.
I've also done a free-flow test (5-10s) and starting at 200F, temps dropped to about 175-180F. Before this mod, 5-10s free-flow dropped to 160F or lower, so this mod does help maintain temp stability. I need to test futher, but the result is in the espresso. It's difficult to explain but I believe my espresso has been good since PIDuino, but with the preheater coil... the taste has been 'accurate', well defined. Indon't know if that makes sense or not.
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