How to do citric acid bath?

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

Postby jgrosjean » Aug 04, 2019, 6:54 pm

I have an old machine that I'm trying to restore:

Rancilio S27 - Restoration?

Since I have it disassembled I plan to descale by putting parts in citric acid bath. I guess 1 tablespoon citric acid per liter. I know things like copper tubes, boiler, and group head should go in. But I don't know what else. In photos I "think" I see people putting lots of other stuff like:

- Pump?
- Flowmeter?
- Solenoid valves?

Also I'm not sure what parts to leave out. I think maybe:

- Don't put in gaskets?
- What about bolts and nuts used to hold things together? For example bolts that hold down power clips for heating element. Do they go in?

Thanks for any tips.

forbeskm

Postby forbeskm » Aug 04, 2019, 7:31 pm

Nothing chrome should go in as I have read long term it will make the chrome go away. Basically the only things that needs to go in would be those things in the water path that have the possibility of scale. So the plate with the holes on the solenoid but not everything needs a bath.

Others may have there ways. I find joeglo is great for everything else. Disintegrates coffee oils with ease

nirdvorai
Supporter ♡

Postby nirdvorai » Aug 04, 2019, 8:25 pm

For the flowmeter- look at the link below for how to clean it.
I used this method while restoring my Astoria CKXE.

http://www.espresso-restorations.com/flowmeters.html

Sw1ssdude

Postby Sw1ssdude » Aug 05, 2019, 1:55 am

Nickel does not hold up in a citric acid bath, but i guess its due to the underlying copper dissolving. but i guess you dont have any nickel plated parts.

i also noticed that brass parts become a red hue, as if the copper in the brass emerges to the surface. but this cleans easily with a soapy sponge.

also, i would not use a hot bath. there is a chance that the scale forms a chemical bond with the citric acid, leaving a residue that looks and feels like lime, but is no longer dissolvable but in ice cold high concentrated citric acid.

never mind the gaskets. since you have the machine apart it would be the perfect time to replace them anyway...


good luck, send some pictures!
Lean Mean Caffeine Machine

jyl
Supporter ♡

Postby jyl » Aug 05, 2019, 8:25 am

I used citric acid when restoring my Elektra. i found it didn't do much unless the water was rather hot. I ended up with everything in an insulated cooler that I filled with hot water + citric acid and to which I added boiling water daily. The parts stayed in there for several days. Even with heat, the action was very slow. I used more than 1 Tbsp citric acid per 1 liter water. Probably 2x that.

White vinegar is more effective, and does not require heat to work well. I used a vinegar bath, up to a day or two, for small parts like group, valves, fasteners. I've read that it will leave a taste. I haven't noticed that but I didn't use it for the boiler.

I put chromed parts in the vinegar without issues, although I did check them from time to time to see if anything bad was happening. I didn't try them in the citric acid.
John, Portland OR
Vintage bicycles, Porsche/VW, cooking, old houses.

pnassmac

Postby pnassmac » Aug 05, 2019, 9:26 am

If I may ask, what material and size is your boiler and how did you descale it?

nirdvorai
Supporter ♡

Postby nirdvorai » Aug 05, 2019, 9:33 am

If I may ask- why not put everything in descale solution instead of citric acid?

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hankbates

Postby hankbates » Aug 05, 2019, 11:11 am

jyl wrote:White vinegar is more effective, and does not require heat to work well. I used a vinegar bath, up to a day or two, for small parts like group, valves, fasteners. I've read that it will leave a taste. I haven't noticed that but I didn't use it for the boiler.


Calcium citrate is relatively insoluble and has a tendency to plug small passages.
Calcium acetate is quite soluble and does not have this problem.
rpavlis said that the only problem with using vinegar is its tendency to make the coffee taste like a salad if not thoroughly removed.

Coffcarl

Postby Coffcarl » Aug 05, 2019, 11:51 am

So if your espresso blend is rather "flat" you can add some "brightness" by descaling with vinegar!

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homeburrero
Team HB

Postby homeburrero » Aug 05, 2019, 2:32 pm

hankbates wrote:Calcium citrate is relatively insoluble and has a tendency to plug small passages.
Calcium acetate is quite soluble and does not have this problem.
rpavlis said that the only problem with using vinegar is its tendency to make the coffee taste like a salad if not thoroughly removed.

+1

Vinegar has the advantage that it's also is a weaker acid than citric, and if you use white vinegar (5% acetic acid) you have a relatively tame and safe concentration. It will take more time but that's an advantage if you are keeping an eye on it when soaking chrome or nickel plated parts. Either will work faster if the bath is hot.

Full strength white vinegar (5%, about 0.8 Molar acetic acid) is quite a bit less acidic than citric at 1 tablespoon per liter, even though the latter is only about a 0.1 Molar solution. Difference in initial pH would be about 2.4 for the vinegar and about 2.1 for the citric. That may not look like much, but because pH is a log scale it means the citric has over twice the concentration of [H⁺] ions. The citric would work faster and be more corrosive, but would dissolve less scale before it was neutralized (you may need to change to fresh descaling solution more often.)


Having said all that, I should mention that Paul Pratt, who has maybe been there and done that more than anyone, says he uses citric to descale disassembled parts, and sometimes tries both sulfamic and citric on tough jobs.¹ Sulfamic is a far stronger acid than citric,², so you would need to be extra cautious - best to use a commercial descaler per instructions for that.


¹ per Faema E61 Legend Scale

² pKa values:
Sulfamic 1.1 (almost a strong acid)
Citric (I) 3.1
Acetic 4.7
Pat
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