The Dirty Portafilter

My corner of the Internet, mostly espresso related but occasionally life will interfere.

Wednesday, December 28, 2005

Isomac Millennium Mods Revisited

I made a few more alterations to my Isomac Millennium. Even with the oil dampened pressure gauge, I was getting way to much flutter. This not only renders the gauge nearly useless, but will lead to a speedy demise of the gauge. The constant pulsing will blow the diaphragm out of the gauge. I also wanted to reinsulate the boiler. The pipe insulation I had original used had a very low R value and does not provide adequate insulation.

I managed to find the adaptors to convert my ¼ inch T fitting to a 1/8 inch OD pipe, and from the 1/8 inch OD pipe back to the 1/8 inch NPT fitting on the gauge. I purchased 4 feet of soft copper tube and wrapped it around the handle of a screwdriver to create the coil. The smaller tubing, longer length and coils eliminated the entire pump pulsing. The gauge now operates without any flutter

I pulled the pipe insulation off of the boiler. I used some ceramic foil backed insulation I had left over from a wood burning stove installation. I wrapped the insulation around the boiler and end caps. It does not look pretty, but works very, very, good. With the machine heated and running at 1.3 bar, I can put my hand on the foil backing. It is no hotter than a heating pad.

While I was in there I decided to play with the Pstat setting. I have one of the older pstats with the deadband adjustment screw. I gave it a very small turn to tighten the deadband, and made a very slight increase in boiler pressure. I am getting a .05 deadband now. The boiler cycles from 1.25 to 1.3. I found that to be quite shocking. I did not expect any change.

Unfortunately, with the added insulation, the boiler is now too hot. It steams like a champ, 8 seconds to stretch and about 15 to heat, 15-20 seconds to steam total. I have to run an absurd cooling flush and the HX is overheated in just a few seconds (15-20) so I am constantly pulling 8 oz (or more) flushes to cool the unit before extraction. I am almost afraid to touch the Pstat fearing that my nice tight deadband will go away, but it has to be adjusted down.

Sunday, December 25, 2005

Merry Christmas

Merry Christmas world.

Thursday, December 15, 2005

Caveat to Lever Machine Temperature Controller

Here is the problem, these types of machines require at least .5 bar pressure to operate, that is around 228F water temp, much higher than the accepted norm of 205 for brew water. Even after I added the digital controller my water temp at the grouphead is still to hot. It is better and I do notice a difference, but was it worth all of the work, still undecided.

I let my machine preheat for about a half hour at 190F, then I ramped the temp up to 230F (brew temp), took a type K thermocouple and held it suspended in the opening of my single spout PF. I raised the lever and watched the temp. After about 8oz of water it stabilized at 213F. I have to assume that if I was pulling a normal shot the temp at the shower screen would be lower than that due to group head temperature, but after slowly streaming out 8oz of water it was hot.

Now for the sake of fun, I let it cool, repeated the process but ran the temp up to steam pressure, 242F (about 1 bar) and took the water temp using the same method. That is about where the machine ran at using the OEM pressurestat. Guess what the water temp was, 213F again.

So in the end, the water I got from the machine at the lower setting, and the water that would have been dispensed at the normal pressure level appear to be the same. I have to emphasize, appear. While I do have access to a couple thermocouples, I have no desire to spend hundreds of dollars on testing equipment. I have become somewhat less enchanted with all of the tech tricks and gizmos over the past month and gone back to concentrating on what is most important. My barista skills and what ends up in the cup.

So take it with a grain of salt. Can you improve on the stability of these styles of machines, yes, but is it worth all of the work, undecided. You also loose some of the old world classic design by putting a digital controller or big old variac on the counter beside the machine.

Tuesday, December 13, 2005

Digital Temperature Controller on a Lever Espresso Machine

One inherent problem that the Pavoni style lever espresso machines is overheating. After a couple of shots the grouphead starts to overheat. The only remedies would be turning off the machine and letting it cool down, some try wrapping the grouphead with a cold towel and others wash the portafilter in cold water to draw the heat out of the grouphead.

Part of the problem was that there is no temperature control on this type of machine. While there is a pressurestat to regulate the temperature, making quick adjustments was impossible. What you essentially have is a single boiler espresso machine that always operates in steam mode.

So one day I thought to myself, why not add a PID controller so I can adjust the temperature. After a quick search for controllers my hopes were quickly dashed, I did not want to spend $150 for a controller. I did not need fuzzy logic or the tight band that a PID provided. Then I say Jim’s post about a low cost thermocouple probed digital temperature controller.

Using this low cost controller, I can set the temperature low for brewing and then raise it for steaming. The unit contains a 15 amp relay which is ample for the 1000W heating element the Factory uses.

My list of parts:

Digital temperature controller $50
OmegaLock compression fitting $5
Type K Thermocouple $20
Project box, split loom tubing
Grommets, and switch (RadioShack) $15
Total cost of parts $90

I started by removing the bottom of the machine. The assembly is very simple. You have a line that runs from the switch to a thermal breaker on the bottom of the boilerplate, then to one of the heating elements. Another line runs from the switch, to the pressurestat, then from the P-stat to the other heating element. So all I needed to do was remove the boilerplate, drill and tap the hole for the fitting, run the power line that goes to the Pstat to the controller and put it all back together. It is actually very simple.

So I removed the bottom…



Removed the boilerplate. It is held on with 3 Allen screws, be careful not to break the rubber O-ring seal.

Drill and tap the plate but make sure your probe will be centered between the heater coils.



I drilled a hole in the center rear of the machines base and inserted a rubber grommet.

Mark the controller location on the project box and cut your mounting hole. I also drilled a hole in the rear center of the project box and installed another rubber grommet. I drilled a mounting hole on rear top of the project box to install a power switch for the controller. Run your wires from the espresso machine to the project box. Hook up you wires and mount the display. I used two small beads of hot glue to help secure the display to the back of the box. Then I put a bead of hot glue on the wires and grommet (inside the box) to act as a strain relief and likewise on the wires as the exit the espresso machines grommet.

Sorry for the poor quality photo. The strobe flash on my little digital camera burnt out.



Then reassemble everything, fill the boiler and power it up. Set the temp low (say 190F) and let it heat. Then check the fittings for water leaks. If there are no leaks, up the temp and pressurize the boiler (say 225F, about .5 bar) and once again check for leaks. If all is good, then ramp the temp up to full pressure (245F, about 1 bar) and check for leaks.

If there are no leaks, let the unit cool and put the bottom on the machine. Put the exposed wires in the split loom tubing and you are ready to go.


Sunday, December 04, 2005

Espresso Exchange

I am participating in an espresso blend roast-off over at OpenCoffee. There are six participants including myself, two of which are professional roasters. Check it out for more information.