Posted Thu Feb 23, 2006, 12:25pm Subject: Gaggia Passive Preheat
I promised to post the results of my attempt at preheating the brew water using coils of 1/4" tubing. I had the day off on monday so I went ahead and tore into the project.
I purchased thin walled copper refrigerator water line tubing from home depot and measured the tubing volume using a syringe and came up with just over 7 ml / foot. I removed the boiler from the machine and removed the steam thermostat and the steam valve from the top. I have a PID on the thing so there's no brew thermostat in the way on the side. I coiled the tube on a 2.5" piece of pvc pipe then spiraled the tube around the boiler, opening up the coil as needed. I didn't attempt to match the shape of the boiler so the coil is fairly circular around the rectangular boiler and about 3" in diameter. I used the original plastic tubing and connections to the boiler and the pump using standard 1/4" compression fittings. After putting it all back together I fired it up and immediately sprung a leak. If you try this, buy several compression rings/nuts/bushings and choose the tightest combination. I was able to coil 10 feet of tubing around the boiler which gives me something over 70 ml of water sitting in the tube.
Before doing this, I measured the brew temperature using a thermocouple on the top of the puck. A brew cycle would start out at 205 deg and drop to 198 by the end of a pour. Afterwards, the measured drop went from 205 deg to 203 deg. It also seems to warm the water about as fast as I use it since measurements on 2 consecutive pulls have been the same.
I need to monkey with the brew temp a bit more to see if changing the PID set point down a couple degrees will make a difference in the final cup, but i've already noticed that shots are more consistant and smoother. My wife, who has the more sensitive palate, has also indicated that the coffee has "been better lately". I use her as the blind taste tester since she is happy to let me tear the machine apart in the kitchen, but doesn't really want to know the gory details of the thing.
The disadvantage so far is that the copper tubing vibrates on the boiler as the system pressureizes so it's a bit noisier at the start of the shot and when I'm flushing/cleaning. I've only brewed ~12 shots so far, so time will tell if the connections are solid enough to handle the vibration/pressure.
The attached photo is from the back side showing the connection to the pump at the bottom left and the connection to the boiler at the top center. I have a top view, if anyone is interested.
To understand this correctly, you're holding resevoir water in the copper tubing wrapped around the boiler to preheat the water that will enter the boiler when the pump is activated. Is that right? I would worry about copper taining the water, honestly. Not per each shot, but overtime for sure. It's definitely more surface area exposed to the likelihood of scale.
Have you done a comparison measurement of temeprature of the shot on top of the puck? You listed one measurement only. Just curious.
Hot-rodding a Gaggia coffee.. I swear you're the only one haha.
I thought of doing this too, but actively, by assisting it with some sort of rope heater or something of the like.
Just out of curiosity, where is your thermocouple located for your PID? I got a washer thermocouple and put it between the (now a dummy) brew thermostat and boiler. I am starting to think that maybe this is too close to the heating elements, so I am not getting a very direct reading of the boiler temperature.
What do you set your PID to? I have been running mine at about 208 with the above mentioned setup.
I have seen pics of the gaggia coffee open - you are lucky, you have a lot more room to work with. My interior(especially near the switch cluster) is a jungle of wires.
A different idea for pre-heat would be to have a small(3oz) reservoir and heat that with some heating elements.
The major issue with adding more heating elements to a gaggia is your current load. The 1500w boiler translates to about 12.5A. I wouldn't want much more of a draw in my old house. I can see the lights all over my house visibly dim as my heater kicks on and off, especially now since it cycles very frequently with the PID.
Jasonian- I don't know about tainting the water- my whole house is filled with copper pipe. As for scale, yeah well, maybe. I'm choosing not to worry, the machine will probably die before it's an issue. The temp comparison is in paragraph 3- a drop from 205-198 before, and 205-203 after.
I'm a wild and crazzy guy!
Silver2k- Yeah, I was looking for a solution that didn't draw more power. I've got old wiring too. My thermocouple is located in the mounting stud for the stock thermostat. I just drilled a shallow 1/16" hole into the top of the stud between the heating elements and inserted the thermocouple into it there with transfer grease. Right now my PID is set at 217 deg. I'm not sure, but the stock is 220 maybe?
Jasonian- I don't know about tainting the water- my whole house is filled with copper pipe. As for scale, yeah well, maybe. I'm choosing not to worry, the machine will probably die before it's an issue. The temp comparison is in paragraph 3- a drop from 205-198 before, and 205-203 after.
I don't know how I missed it. That's pretty impressive!. Now you've got me wanted to mess with my machine.. but I'm too poor for that kind of a project. :o(
Cheap, simple and the parts are available at home depot. What more can you say?
Was surprised that 10' tubing fit. Have you thought about insulating the tank assembly to raise the preheat temperature? Ok, a little less CO2 wouldn't hurt either.
Posted Sat Feb 25, 2006, 8:20pm Subject: Re: Gaggia Passive Preheat
The mod is not as easy as it sounds. Don't think the connecters on my Gaggia are compression fittings. The plastic pipe has a ridge at the end to make the seal. Is it a flare or o-ring fitting? Additionally the instructions on the compression fitting suggested a barb connection for plastic pipes. Since I didn't have the parts and I didn't have a spare pump-boiler water line, I canned the modification. Oh well, at least I replaced the boiler o-ring and cleaned out the boiler.
Of course, my gaggia is not a typical machine, a '93 classic in Bunn shell. Also space was pertty tight to add the copper tubing.
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