Conti Prestina Espresso Machine Restoration 101 (Completed and Indexed) - Page 15

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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drgary
Team HB

#141: Post by drgary »

Thanks Ray and everyone else who's weighed in on how to PID this machine. One of the nice things about a leisurely restoration is having time to ponder before next steps. I've decided to not PID for now. Here's my reasoning:

1. The mechanical era engineers who designed this machine optimized it for temperature sufficiently by combining a PSTAT and large group mass. Adjusting the PSTAT may be sufficient. Others who use these commercial levers note their forgiving nature inherent in the smooth and tapering pressure profile of a large spring lever.

2. I don't know if the clacking of the PSTAT will bother me. If so I can always PID later.

3. With its large 4 liter boiler, massive commercial group and modest 1000 watt heating element, this machine will warm up slowly and remain stable at temperature. I think of it like a commercial truck versus a motorcycle (in contrast, my Pavoni Europiccola heats in less than 15 minutes and responds quickly to on the fly temperature adjustments).

4. Ray's cautions about overheating a solid state relay remind me that additional electronics provide more potential points of failure.

5. Eagerness to reassemble and try out -- no need to add another complex task to the restoration for now.

6. A shortfall of a commercial machine like this without a PID is it may be harder to adjust temperature for very different coffees, but I don't think it will be quickly responsive to fine heating controls anyway and I have other machines for that.

7. I can always PID later but would keep a PSTAT inline anyway as a safety precaution.

8. Added: I'd like to avoid the clutter of a project box on my counter for now. I would hesitate to cut into the face plate to install a PID on a classic machine like this and want to stay as close as possible to a stock look. (I'm also thinking of reproducing the drip tray as close as possible for that reason, and there's a suggestion earlier in the thread about how to do that.)
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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allon

#142: Post by allon »

These are exactly the reasons I'm leaving my CMA lever stock to begin wtih.
I'd like to experience it as designed first :D
LMWDP #331

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RayJohns

#143: Post by RayJohns »

You can definitely always add a PID controller later, that's for sure. And that might actually be a smart way to go (i.e. fewer variables to deal with initially).

Also, a 4 liter boiler with only a 1000W heating element may tend to mitigate some of the effectiveness of the PID controller, although I can't really say for sure how big an issue that might be. On my La Pavoni, I use about 800 ml of water with a 1000W heating element and the PID controller can easily maintain the boiler temperature by cycling the heating element on every 2 seconds for 1/2 a second. I'm not sure what sort of impact having a full 4 liter boiler might have. It's possible that the additional thermal mass of the boiler and water may help, not hurt. I don't know. It's also possible that it may require longer cycling time, which could cause the PID controller to have more difficulty in maintaining the target temperature.

I do think the PID controller is the way to go, since it allows easy control of the temperature (and pressure) and is more accurate than using a pressure stat. It's also nice to know the exact boiler temperature you are dealing with at all times as well.

But again, it's relatively simple to add later. I wouldn't worry too much about the solid state relay failing as long as there is some thought to keeping the temperature of the relay in check via the use of a heatsink.

Ray

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drgary
Team HB

#144: Post by drgary »

Before continuing, I just wasted 1/2 hour writing the latest update and having my browser crash on me before I saved to H-B. Text and many photos were uploaded that now aren't here, but no blame to H-B. I just need to learn to use this site better! If doing a long post, I discovered the virtue of posting incomplete entries to save to the site and then editing them. So here goes, "post in progress"!

Today I did most of the final teardown of subassemblies and immersed them in cleaning baths. I documented this in photos below. I also differentiated parts that are brass and copper versus those that are steel or chrome because of the following thread: Citric Acid, How Much to Use for Heavy Descaling. So in overview, brass and copper parts now sit in strong citric acid solution, chrome and steel parts sit in JoGlo detergent. And the heating element tubes sit in a milder descaling solution of Urnex Dezcal, with the electrical contacts not immersed.

In detail, here's today's progress, starting with disassembling the group screen. I'm showing this level of detail and narrating you through it so you can see what's involved and anticipate the kinds of roadblocks I encountered.

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Next I addressed the water fill toggle assembly, which was fairly complex, with lots of small parts. Here's how that came apart:

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The end plates once unscrewed needed to be "convinced" with a flat blade screwdriver tapped with the mallet.

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This process revealed more gaskets needing servicing.

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Added images: I discovered that I'd missed some old gaskets and disassembly. Here's a brass retainer clip and screen removed in place and then shown separately.

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Added images: And here's a brass washer and rubber o-ring removed in place and then shown separately.

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This photo documentation process has been very valuable. Dave at Allann Brother's looked over these old images and saw that I'd missed the disassembly shown in the four images above. I am now posting them in November 2012.

Returning to images that had been previously shown here, the group cylinder still had the siphon attached.

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Some gentle persuasion with a wrench and mallet got it off. Note the different color inside the cylinder. The part itself is brass but the cylinder walls are chrome plated. This means it will get a gentler cleaning than the other brass parts.

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The browser crashed again. Glad I've been saving as I go! :lol:

Another siphon tube presented itself and puzzled me. This is from either the steam or water valve. I couldn't tell whether it's removable from the other fitting or is firmly connected. Scale partly concealed a gasket.

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So I applied a propane torch for about 30 seconds, and cooked the gasket, which I scraped away with a picking tool. Further attempts to turn out the siphon tube failed. I tried inserting a phillips head screwdriver into the tube and turning it. No go. Then I fit a long-nosed vise grip pliers, and it started to bend the tube. So I stopped and assumed it's all one piece!

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Next I addressed two identical parts from the steam valve and hot water valve. Both showed brass washers that were glued on with limescale and crud.

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A tap of a flat head screwdriver with the mallet, and this came loose on both identical parts. When one of them bent, I straightened it by putting it in a vise and tightening down.

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People caution about doing unnecessary assembly, and this can be precarious with complex devices, such as the manometer assembly here. But I've found that taking these subassemblies apart in a machine this long neglected often reveals hardened gaskets needing replacement. Case in point: Here's disassembly of the manometer connection.

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Now that I was gathering parts for immersion, they no longer neatly divided into the plastic bags I'd catalogued. So I had to document some of those things in photos to know how to reassemble once everything's clean. In this next photo, the heating element is obvious for what it is, but the other part that feeds water through the boiler plate might be hard to recognize.

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Now it was time to sequester different parts into different baths. The heating element needed special treatment because its electrical contacts can't get wet. So it got its own glass and a mild descaling bath of 1/2 oz. Urnex Dezcal in 2 cups of hot water.

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All the chrome and steel parts (and this would apply to aluminum too) went into a hot bath of 2 1/2 quarts water and 2 heaping TBS (tablespoons) JoGlo detergent.

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And all the brass and copper parts, including the grimy boiler faceplate and boiler went into a hot bath of more intense descaling solution, comprised of 1 lb. of citric acid in 10 liters of water.

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This went out onto the patio, just in case the plastic bucket holding this stronger acid breaks down. In that case, I'll get some very clean concrete! BTW, this isn't the strongest acid bath people write about on this site. 1 lb. citric acid to 10 liters of water is a bit under 5 TBS per liter. Sorry, I can't tell you the PH. But those parts will be clean!

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Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

ulrikmo

#145: Post by ulrikmo »

Hello Gary, wise with the photodocumentation, this will save you for trouble once getting to the assembly. Nice with all the photos of your progress, I bet you can't wait to see the parts getting out of those baths all nice and shiny :D I wondered if you could take the measures on the tube feeding the group, the one dipping down into the boiler, once you have it out of the bath? I am currently gathering information on various dipperfed levermachines on the aspects affecting flow to group. The measures I look for is the inner and outer diameter of the pipe.. Good work and good luck with the rest of your restoration!
Ulrikmo

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drgary
Team HB

#146: Post by drgary »

I'll be glad to measure that tube. Can you say more about your research? (Sorry to be nosy, you must be an engineer designing a commercial lever machine. I'll measure it for you whether or not you can tell us about your project.) Later add: Your profile lists you as an M.D. ... not likely you're an engineer at Gaggia! :lol:
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

ulrikmo

#147: Post by ulrikmo »

Hello Gary, no engineer at Gaggia, although it could probably be exciting :D This is just a personal research, not very scientific at the moment. I have just been wondering how different designs of dipperfed levers might affect flowrates and maybe even preinfusion. Normally I work with the physics of the human body, so this is a somewhat different area, as for many a passionate hobby, where I try to understand the physical background for the different designs. Was that an answer? I will start a thread someday, for those interested, but thought it would be good with some background research before I jump out in it..
Best regards
Ulrikmo

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drgary
Team HB

#148: Post by drgary »

ulrikmo wrote:I have just been wondering how different designs of dipperfed levers might affect flowrates and maybe even preinfusion. Normally I work with the physics of the human body, so this is a somewhat different area, as for many a passionate hobby, where I try to understand the physical background for the different designs. Was that an answer?
Ulrikmo
Sure! For many of who have wandered to this site, the propeller on top of our heads spins a little faster than it does for the general population. It sounds like you have twin props! :D
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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drgary
Team HB

#149: Post by drgary »

Another part to catalog, with the brass thrown into the strong citrus bath and the glass in the milder descaling solution. Here's the sight glass disassembled:

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Tomorrow the parts come out of the bath, and I'm told the powder coated and chromed parts are on their way back to me.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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drgary
Team HB

#150: Post by drgary »

ulrikmo wrote:I wondered if you could take the measures on the tube feeding the group, the one dipping down into the boiler, once you have it out of the bath? I am currently gathering information on various dipperfed levermachines on the aspects affecting flow to group. The measures I look for is the inner and outer diameter of the pipe.
The inner diameter of that tube is 11 mm, the outside is 14 mm.

I'm just taking these parts out of the citric acid bath and am struck by their redder, copper color instead of the yellower bronze color they appeared before cleaning. I wonder whether citric acid accentuates the copper content of the bronze in some way? Image

The heating element is stamped with its wattage and voltage and an apparent manufacturing date of January, 1978.Image

Removing some dirt from the group head mount revealed a gasket and o-ring that I removed with a picking tool. But some crud still remained behind the removed gaskets, so I later put this part on the floor and heated it with a propane torch to carbonize the crud for easier removal through brushing or polishing.

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Here's what the boiler and faceplate look like after removal from the descaling bath, where they soaked for a week.

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Some parts still have issues. The cylinder that sits on top of the piston cylinder has rust and pitting, and I would love any advice on how to condition this to prevent further degradation. I can certainly polish off the rust and lubricate this part, but I don't know if that's enough or whether I'm inviting problems down the road.

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The piston cylinder itself looks fully usable. However, it does show some scale on the interior chrome plating. There's rust residue from the part just shown that sits on top of it, and this can be polished off. The third picture may be a clue to its composition. It appears to be bronze plated but may be cast in another metal.

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Although the sight glass sat in weaker descaling solution for many days, it still shows some scale, and I may need to clean that with a pipe cleaning, being careful to not wear off the red indicator line.

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My next step with most of these parts is to do a finer cleaning with steel wool, brushes, detergent, and in some cases like the crusted boiler and faceplate, with a rotary tool wire polishing brush.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!