It has always taken several lectures in a polymer chemistry course to explain why serious problems can arise when elastomers are in contact with solvents. Elastomers such as rubber and synthetic rubber are long chain molecules, polymers. The chains are flexible, and inter molecular attractions are relatively weak. (Otherwise they would be rigid.) A "thermoplastic" polymer is one that has long straight chains of a "monomer" that is strung together to make the polymer. It has very high molecular weight so it generally is not fluid, but it may be a very viscose material.

A "thermoset" polymer has long chains too, but there are periodic "cross links" between different chains in the material. Lots of cross links will make any polymer into a rigid solid. A lighter degree of crosslinking will result in a flexible material that still holds its shape. No crosslinking will tend to result in a "goo" unless the material have crystallinity or extremely high molecular weight. Partial crystallisation can make a sort of pseudo cross link for things like polyethylene. (These turn into "goos" when heated high enough to melt the crystallites. Do not heat your polyethylene things above about 138C!)

Any way, thermoset polymers with light cross link density when placed in solvents in which the polymer would dissolve were it not cross linked, tend to have the solvent molecules get inside the polymer, causing it to swell. Before intermolecular molecular attractions helped hold the things together, now all that remains is the cross links. This makes the material soft and easily torn.

The so called "silicone" (polysiloxane) polymers have very very low inter molecular attractions, and thermplastic versions remain at least semi fluid when they are rather large molecules. Silicone rubber is a version of this with cross links. Silicone polymers with high molecular weight flow slowly, and have weird physical properties, like the famous "Silly Putty." Because the silicones are so large they tend not to fit into spaces in cross linked elastomers. However, silicones are not soluble in hydrocarbons anyway.

Hydrocarbon greases are okay to use with materials that would not dissolve in hydrocarbons if not cross linked. However, they have serious problems with natural rubber and related synthetic ones.

The weird flow properties of silicones makes them unsuitable for lubrication of metal against metal parts. They are ideal for O rings and similar seals.

Perhaps someone at HB knows the compositon of MCAL seals. There are some materials that are not harmed by hydrocarbon lubricants. However, if they be made of a rubber or rubber analogue a petroleum based lubricant is a very bad idea. Petroleum based lubricants are also bad for other materials when they would dissolve the uncross linked material. Silicones are insoluble in almost everything, and the ones that are fluid tend not to dissolve almost anything.

Thank you every ones for your very appreciated help and advices. Specially Robert for your in depth explanation and Craig for the addresses for Dow 111. I know all of those distributors, specifically Canadian Bearings which I make business with.

baldheadracing wrote: As an aside, Stefano's offers Haynes Silicone Grease is an alternative to Dow 111 - for seal/o-ring to metal applications.

This is the same Haynes product I use actually. I'll have to ask Stephano's opinion. But I'll try the Dow 111 for sure.

baldheadracing wrote:Is that lube stained brown - from coffee?

I cannot tell if it's coffee stain or something else. What I can tell is that first time I pulled out the piston, the Elektra factory lubricant was the same brown color. I was surprised to see this color and was expecting to see clear color lubricant as silicone grease looks usually. The Haynes lubricant is coming clear out of the tube as any other silicone looks like. The brown coloration comes from undetermined factor such as contact with coffee, heat, contact with brass or steel, etc. does your lubricant keeps its clear color with time? Maybe a chemical reaction causes this brown color.

I'm quite busy actually but will keep you informed with any success. I'll have to order the bottom seal ASAP.

Regards,

i just wanted to mention that i had serious corrosion issues with the aluminum boiler in my microcimbali while using Brita water. The water coming out of my machine also had that cloudy appearance, but with a grey tint from the aluminum. The Brita filters can make the water very acidic. I think corrosion can be much worse in these pressurized brew boiler designs. Your issue may be as already identified, but if the seals dont fix it, you may need to check the water.

Acid water is very bad for copper or brass boilers. It is amazingly bad in the presence of even small amounts of chloride. Oxide coats do not form properly, and the water ends up containing cupric salts.

I think Haynes makes both hydrocarbon and silicone food safe lubricants. The silicone ones should not give a problem. There are simple test kits that can tell you whether the water be acidic. Some use a compound called bromothyol blue. It is green at pH 7, blue in alkaline water and yellow in acidic. (Aquarium stores sell these kits.) Ideal is just SLIGHTLY alkaline. Bicarbonate ion in water keeps it slightly alkaline, and also tends to reduce the acidity of the final espresso from the carboxylic acids in roasted coffee. (That is why I like to use the wine makers technique using potassium bicarbonate.)

lgxiii wrote:This is the same Haynes product I use actually. I'll have to ask Stephano's opinion. But I'll try the Dow 111 for sure.

Please post back once you hear. I thought that I asked the question when I ordered the Haynes from Stefano's, but I can't find any record of it (and I am old enough to know not to trust my memory ).

I just pulled my group out of curiosity, and, after five months, the lube (Haynes) does have a brown tinge. However, I never have used as much lube as in your pics. I don't know if I am doing it right, but:
- I wipe the cylinder down, pressing hard with my lube-coated finger. This leaves a very thin coat of lube everywhere in the cylinder;
- I wipe an even thin coat on the seals (less than 1mm thick); and
- I give a quick wipe with a paper towel to reduce any excess that gets on the piston and spring, but I don't make a huge effort to get rid of the excess, except on the coffee-facing face and edge of the piston.
Basically, I am doing the same thing as I was taught to do with car brake cylinders, pistons, and seals. My MCaL is 30 years old and the cylinder has visible wear, so my main concern is arresting that wear. Retained coffee grounds (fines) in the cylinder bore are the enemy, so I pull the dispersion screen every dozen or so shots and clean the screen and the o-ring with (unscented) shampoo, and wipe down the piston face. I don't want old coffee affecting the taste of my espresso!

I have another suggestion concerning water. You might try other alternatives. Go to a grocery store and get some distilled water. It is very inexpensive. Rinse out your MCAL with clean tap water and fill it as a first test with pure distilled water. Contrary to what some have posted here and other places distilled water is NOT corrosive. There is also no sense in dumping it after each use because it is pure. Try the result. Depending on the degree of roast and what you like, you may find that great, though with light and medium roast it will likely be sour. (Remember that there is dramatically more Mg and Ca in the BEANS than in the hardest water.)

Try 1 mM sodium bicarbonate. Take a bottle that holds about 100 millilitres. Saturate it with sodium bicarbonate. Its solubility, about 90 grams/litre will produce about 1 molar solution. (MW is 84 grams/mol). Add 1 mL of this concentrated sodium bicarbonate solution per litre of distilled water to make brew water that is close to 1.0 millimolar in bicarbonate. It is very close to the bicarbonate concentration of hard water. You can also try lower concentrations of bicarbonate too and thus have another variable to control.

For another test: Coffee beans contain remarkably little sodium, but massive amounts of potassium. If you use potassium bicarbonate, available from places that sell brewing supplies and some health food stores, also inexpensive, you can use it instead. Its molecular weight is 100 g/mole. It is best to weigh out 10 grams of it and add with stirring water to make 100 mL. Add 1 mL of this concentrate per litre of distilled water to make the brew water. Even though the concentrations are low, you may notice a taste difference between the three solutions, and the last one is most likely to have nearly identical taste to tap water, but will absolutely NOT produce scale, and is probably about the least corrosive to brass or copper brew water that makes sense to use. It is protective of copper and alloys because the slight basicity makes the copper oxide coatings more stable. You do not want the whole periodic table in your brew water! Again you will NEVER have any scale using either sodium or potassium bicarbonate.

Some suggest adding small amounts of magnesium sulphate to the water, but there is so much Mg in the beans that this seems silly to me.