Conti Prestina Espresso Machine Restoration 101 (Completed and Indexed) - Page 31

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

#301: Post by drgary »

orphanespresso wrote:I would guess that teflon or alimentary will be the gasket here to use since they can both squash a little to get the alignment right without a lot of teflon tape fol de rol. What is the plan for the viton? I only use viton sheet to make Peppina washers and Microcimbali disc valves. Pretty spendy stuff for a boiler gasket, and a little soft as well. Get a sheet of alimentary...the green stuff...hard to work with but good for boiler, group to boiler, lots of flat work....really the right stuff as far as that goes if you can tool up to work with it.
@ Doug: I was following this advice a couple of pages earlier. :lol:
orphanespresso wrote:The material should be at least EPDM, HSEPDM, Viton is best (silicone has a higher temp rating but is often too soft for some applications).
I think I've got it solved for this application, alimentary for the heating element gasket. Ray, if Doug says it works he's done enough of these machines that I trust it will work. I'm sure your solution is good too, maybe better, but a working Prestina would be nice and my eye is on the prize. :wink:

Doug: If there isn't alimentary already cut for M16 for the steam and water taps someone with a home machine shop has offered to cut me Teflon if I need it. What thickness would you use?
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

jedovaty

#302: Post by jedovaty »

What material is alimentary made of? What on earth is it? I looked it up and all results indicate it's healing/sustenance.

Dr. Watson (can't resist)

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drgary
Team HB

#303: Post by drgary »

From what Doug tells me I believe it's a food-safe fiber gasket. He also says the material is challenging to work with if you're trying to cut gaskets yourself.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

jedovaty

#304: Post by jedovaty »

Cool. Did you clean out the inside of the valve-body's housing? The brass "t" like shaped thing? I let all my stuff soak in simple green/water mixture that started with boiling water and simultaneously ran it through the ultrasonic cleaner. Inside is still covered in grease, even after scrubbing with a stiff mini-brush.

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drgary
Team HB

#305: Post by drgary »

Yes, I cleaned out all grease with a degreaser. See a page or two back.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

jedovaty

#306: Post by jedovaty »

Yes, I know. I'm talking about the ones below; simple green appears to not be strong enough; I have an orange degreaser as well, but didn't do much, neither did a citric acid cleaning. The insides are seriously gunked up, gooey and tar-like!! I'll keep at it.

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RayJohns

#307: Post by RayJohns »

drgary wrote:From what Doug tells me I believe it's a food-safe fiber gasket. He also says the material is challenging to work with if you're trying to cut gaskets yourself.
A Greenlee punch & a very sharp wood chisel work wonders :-)

Ray

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drgary
Team HB

#308: Post by drgary »

I took a close look at the holes needing o-rings or gaskets. Here is what I saw for the heating element part inside the boiler and the water and steam taps outside the boiler.

Here are the element insertion holes from inside the front boiler plate:

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Here's the fit of the element inserting into those holes:

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Here's the shape of the gasket indentation in the steam and water tap holes from the outside surface of the boiler plate. The photo isn't definitive but eyeballing it shows it's a flat indentation.

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All of these look need flat gaskets, not o-rings. So I begin to think that maybe a washer on top of that would help and perhaps some additional gasket material. The parts diagram only shows a 16X2 part number 2396, which is labeled in French and abbreviated too (!) as "JOINT TORI. 16X2". If I interpolate they're saying it's a joint o-ring 16mm i.d. by 2mm thickness. But McDave tells me the stems of these tend to turn. That suggests that maybe the softer rubber o-rings he's used aren't as stiff as the Viton that's needed here. Let's see if the Viton will hold in place better. My .07 Viton sheet is almost 2 mm thick.

I also looked at specs of the material that would be suitable. It says at McMaster-Carr:

"Buna-N (Nitrile) Rubber—Use with water, salt water, waste water, sand, ethylene glycol, hydraulic oil, petroleum oil, gasoline, diesel fuel, and citric acid. Not rated for pressure. Temperature range is -65° to +275° F. Color is black."

Steam temperature at about 10 bar per a steam table is over 355F. This rules out Buna. So, the o-rings I was sent would melt down. Added later: Wait a minute! Espresso machines push water through the group at up to about 10 bar. The pressure in the boiler had better not be much more than 1 bar, maybe 1.2 bar for a commercial machine. At 1.5 bar temperature would be under 233 F and this machine has a 1000W element for a 4 liter tank. And yet something with higher temperature rating than Buna seems a better choice for surrounding the tip of the heating element itself.

"Viton® Fluoroelastomer—Use with water, salt, detergents, varnish, ethanol, and biodiesel. Not rated for pressure. Temperature range is -40° to +400° F. Color is green."

So, Viton will work. I received some .07 inch Viton sheet today. I like the thickness and balance between flexibility and hardness. It isn't squishy like the thicker Durometer I've got. I can use a punch for the 16mm inside diameter of the gasket. The lip on the steam/water tap hole is 2mm across and flat. I would use an 18mm punch first then center a 16mm punch inside. Alternatively it may be better to order a circle cutter for situations like this. I have not found flat Viton gaskets of these measurements online. Phillip Canuck offered and sent two alimentary gaskets. To fit the heating element ends they'll need to be 3mm thick with a 12mm inner diameter. If they don't fit I'll attempt to cut gaskets from my Viton sheet.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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drgary
Team HB

#309: Post by drgary »

Finally Some Progress!

I've spent enough time contemplating gaskets. Today I was able to cut some and get them installed and was finally able to start reassembling the boiler. (Added: The small brass fitting above and to the right of the group port where the manometer pipe will attach is in backwards. Reverse it so there are more threads and a bigger hole facing out.) Here's where I ended the day:

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It began with fitting Viton gaskets to the heating element and steam and water taps. I had to cut them first and did this on a plastic cutting board using leather punches approximating the metric sizes and trimming where needed with a box knife and scissors. I measured with a caliper and got to work.

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I was able to size the element gaskets but moving them into place. Any part that was too large was marked by the entry hole. Then I cut it away and was able to fit the gaskets entirely inside.

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Next I assembled the steam and water valves and closed them off with c-clips.

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Then there was a connector to fit with gaskets. All gaskets were lubed with Dow 111.

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The other side of this and some of the other pieces were sealed with PFTE tape, following McDave's instructions, the lack of other fittings in schematics and what I had found in disassembly.

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It was very satisfying to finally insert new boiler bolts, nuts and washers. Remembering the frozen bolts encountered at the start I slathered them in food-safe anti-seize compound. I used the thicker Durometer gasket material to join the valves with the extenders as their softness filled the space better. (Added: As above the manometer pipe fitting on the boiler is inserted backwards in this photo. There are more threads on the other side, and you'll need them to attach that pipe. You can see that fitting through the gap between the large brass hex steam and water valves.)

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Another satisfying moment was realizing I now need to mount the boiler on the frame for the next step.

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I cleaned the dust off the powder coated frame pieces, searched for the fastening parts and found them still rusty. Following Dan Reimer's suggestion in another thread all of those parts are now soaking in molasses diluted by water 10-1. They'll sit there for a few days as the rust dissolves. Tomorrow I hope to address other aspects of reassembly. Today was a good day.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

jonny

#310: Post by jonny »

Good work, Gary! That element seal looks way more appropriate.
Could you share with us more details about your food safe anti-seize compound? What is it and where did you get it?