pasgal

I have read over the years and on various sites, people talking about the pros and cons of stainless vs copper. Unfortunately the area is rife with misunderstanding and misinformation. So here is my take on it, having machines with both types of boilers and seen the problems/issues over a 20 year period.

The statements below are not quite accurate or truthful but are widespread on the internet. I will quote some of the things you will read on the internet….where there is overlap I have made it a single point

Copper Benefits:

• Best thermal conductor, good conductors of heat.
• Copper is highly malleable, ductile, and most importantly has unmatched electrical and thermal conductivity (unlike stainless which performs very poorly in this regard)
• Most expensive (pricier than aluminum, brass, and steel)
• Antimicrobial properties Stainless is thought by some to be more hygenic than copper, but that is not the case either
• Less resistant to corrosion than stainless steel, Copper boilers do not degrade quickly. Critically copper will not rust as stainless will
• Flexible and can endure mechanical stress, does not suffer from metal fatigue from the repeated heating and cooling cycle that a boiler is subject to
• Copper boilers hold steady temperatures well.
• Copper boilers are cheaper to produce than other boiler types.
• Copper boilers can produce excellent espresso if they are made and treated well.
• copper does not have any lead in it, it is not an alloy, it is a pure metal

Stainless steel AISI 316L specifically:

• Stainless steel boilers last for a very long time.

• Stainless steel boilers do not negatively affect the taste of espresso (no copper taste)

• Stainless steel boilers are not damaged by descaling chemicals

• Stainless steel boilers produce very clear espresso.

• cheaper than copper and brass boiler construction

Now sadly, other properties of stainless, that are not always mentioned.

• Very good when you want to undo a boiler fitting (this can be problematic on stubborn fittings in copper)

• Most fittings now, are confined to endplates, which if thick 8+mm can be directly threaded (no brass braised fitting, which is prone to leaks). Sometimes a reducer stainless fitting is used on larger holes, done correctly, still super resistant to leaking.

• A correctly made stainless boiler should outlast a copper boiler by decades. I’m talking about the stainless boilers with a proper thickness, not the bean can thin variety you might find in a Chinese machine and a few others from yesteryear.

  More manufacturers understanding galvanic corrosion of brass, when wetted in contact with steel. So it’s not usually a problem (e.g. a a brass thread in steel with water in the thread and thread to steel contact), because of sealants or PTFE tape which prevents corrosion by both occupying the space and preventing metal to metal contact. It does mean an external O ring or fibre washer should never be used for sealing a brass fitting to copper. Any coating of fittings is very helpful.

Clearly more and more AISI 316 boilers are appearing and companies of yesteryear who may have used different grades for certain steam boilers, are hopefully moving to AISI 316L. …for chinese machines..who knows?

So lets go back to copper and dispel (explain) why some some myths persist if we can

• Best thermal conductor, good conductors of heat. - This might be important in a steam boiler (Casey Jones), or other types of boiler that are externally heated. Get that heat to the water quick. An espresso machine boiler has the heating element on the inside, good heat conduction is the last thing you want and the reason we insulate boilers!
• Copper is highly malleable, ductile, and most importantly has unmatched electrical and thermal conductivity (unlike stainless which performs very poorly in this regard) - Copper is indeed highly malleable and ductile as people have found out when removing stubborn threadlocked or siezed fittings and damaged their boiler. It doesn’t really benefit anything for it to be soft! Electrical conductivity is a non issue and a non benefit and the terrific thermal conductivity has been covered above.
• Most expensive (pricier than aluminum, brass, and steel) - This really isn’t a benefit, being expensive and a lot of that expense is in fabrication by brazing and brazing brass endplates to copper (a source of week and leak points)
• Antimicrobial properties Stainless is thought by some to be more hygenic than copper, but that is not the case either - It’s a boiler, it’s really hot, bad stuff that will make you ill dies.
• Less resistant to corrosion than stainless steel, Copper boilers do not degrade quickly. Critically copper will not rust as stainless will - Partly correct, less corrosion than some stainless steel, but not less corrosion than all stainless steels especially e.g. AISI 316L. Many times I have seen copper boilers from machines less than 20 years old with pinholing around the brazed joints and in the body of the boiler itself (usually seen as green dots).
• Flexible and can endure mechanical stress, does not suffer from metal fatigue from the repeated heating and cooling cycle that a boiler is subject to - Stainless steel AISI316 boilers have shown no tendency to fail due to metal fatigue caused by heating. In the La Marzocco An FAQ where the answer is always “Yes.”, there is the question are your boilers stainless steel. Perhaps La Marzocco don’t know what they are doing, but in my experience they are not choosing stainless steel (AISI 316L) because it’s cheaper, if Copper was better, they would use it!
• Copper boilers hold steady temperatures well. - Complete rubbish, a correctly programmed PID system holds steady temperatures well
• Copper boilers are cheaper to produce than other boiler types. - It probably ends up cost neutral for the smaller boilers, but copper boilers are definitely more expensive for larger boilers.
• Copper boilers can produce excellent espresso if they are made and treated well. - It’s really hard to get away from that copper taste until they scale up (which you don’t really want). Try cooled water from a non scaled copper boiler…urgh.
• copper does not have any lead in it, it is not an alloy, it is a pure metal - Absolutely correct, but if the brass endplates are not Zero lead (not low lead), then it will. You can tell if an endplate is Zero lead, is it silvery, not yellow! The statement about lead was made in relation benefits vs steel boilers, but last time I looked steel has no lead in it either. Of course 316L steel doesn’t leach anything into the water, whereas copper boilers leach….well copper into the water.

Nickel plated copper and brass

Pinholes in boiler

ooh dear

https://www.gasmaster.ca/articles/316l-vs-439-stainless-steel-comparison/

I hope this has helped dispel some of the well meaning, but incorrect statements about copper boilers..clearly retailers and manufacturers who use copper boilers will sit one side of the argument and that’s probably not my side. Stainless steel boilers used to be very hard to make, especially for the small boutique espresso machine companies. The corporatisation of espresso machine companies and increased buying power led to the rise of the AISI 316L espresso machine boilers and associated manufacturers. As the quantities increased they became cheaper so all espresso machine manufacturers, small and large, could now use them. IMO they are a major advance in boiler construction, making in life maintenance of the machine much easier and reducing worries about descaling, or low mineral water.

The Lelit Bianca uses a flow control valve and some people add the Lelit flow control valve to an existing machine. Many owners assume is maintenance free, it’s not and without maintenance can cause problems as the O rings inside the valve degrade. These apparently fit the coffee sensor version as well…see end of post.

• reduced flow
• difficulty in controlling
• no flow
• leaking at the top of the valve spindle

Fortunately, the valve is easy to maintain and problems are easy to fix. The following 2 videos show the internals of the valve and how it works, plus the installation process.

The original O rings are EDPM and sized as follows…I think FKM (Viton) is better, comes in green or black colours and interestingly ECM use FKM on their valve.

EDPM or FKM (I think might be better) size 6.07 × 1.78

My recommendation would be these…but the company does EDPM as well. certainly in hotter HX machines, I would choose Viton

https://simplybearings.co.uk/shop/p512590/BS010-1.78mm-Section-6.07mm-Bore-VITON-Rubber-O-Rings/product_info.html

Maintenance

These systems are not maintenance free and often it will depend on usage. From the factory, I think the valve manufacturers use insufficient lube, so this might be something you wish to check. I lubricate the O Rings with Molykote 111, as I believe it is the finest all round lubricant for espresso machines, but must always be applied to a totally dry surface. It’s fine for Viton (FKM), or EDPM, but should not be used on Silicon seals as it causes them to swell.

Maintenance should be every 3-6 months depending on usage and would involve removing the valve as lubricating the parts described in the first video, remember, it must be completely dry. It’s important to avoid moving the valve until the machine is hot, to prolong its life.

Eventually the O rings will degrade, and then it’s time to pop replacements in. If you bought a bag of 50 O rings (£9.29 delivered!), you can change them annually for less than 40p per year….you will be good for the next 25 years 🙂

If you have an ECM valve split it and do the same…I think the ECM o rings are the same size, but I forgot to check with them when I was over there.

Apparentl; these fit the coffee sensor flow device as well.

Some BS010 Viton O-rings, from the FAQ on Lelit’s Flow Control Valve (thanks DavecUK ) - they seem to be the correct size for Coffee Sensor’s flow control device as well (the green O-rings in the picture are the ones that came with the the Coffee Sensor device. The blacks are new).

Comments from one of our members @Doram after changing the O rings in the coffee sensor flow valve above.

I just pulled the first shot after servicing the flow control device and replacing the O-rings and I was completely shocked by the result. Not only was the action of the valve so much smoother, I was actually able to control the flow completely, stop it, hold the pressure where I want it and get instant reaction from the manometer - all things that I was NEVER able to achieve before!

Until today, when I tried to almost close the device for pre-infusion a few seconds after lifting the lever, I could slow the ramp up a little, but that was about it. Then when I would tale off the pressure to end a shot, there was a delay in reaction and I would usually go down to about 6 bar to end the shot. I saw videos of people holding pressure for long periods (at 2-4 bar for example). In those videos, manometer reacted instantly to closing/opening of the valve. Mine didn’t do that, and I just assumed that my machine/flow control device are ‘different’. What a fool I was! I now realise that when I first got the device I damaged the O-rings by opening the valve too much. The valve probably never sealed completely since then, so I was only able to make small changes to the flow, but not control it completely. With the new O-rings and some lube, I finally get to play with the flow control device as it should be (I hope I am not getting carried away here - this was just one shot and I still have to play and confirm the above, but couldn’t resist sharing already). For anyone who is as stupid as me, your FAQ is priceless.

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For the Lelit Valve (coffee sensor one is probably the same, but I don’t know) Some people have experienced the valve becoming very stiff under pressure, or had the thread in the brass nut that the adjustment pin thread runs in, fall out.

Resellers can now order the threaded nut using the code 2200095L1 Obviously, any resellers you contact won’t know this, but if you give them the code they can investigate. They don’t have to buy the entire valve. I don’t know how much the nut will cost…but I wouldn’t think a huge amount.

As always preventive maintenance is better than replacement, so lubricate every 3 months or so and always before it gets stiff. If you begin feeling any stiffness…lubricate (that didn’t come out right did it?).

In fact I would recommend removing the valve from a brand new machine and lubricating it, before even using it.