Piston seals

Martin ismail

So I had the the problem of lever slipping on my L1 with a high biting point, I decided to try the silicon seals from Cafelat which seemed easy to fit after watching on YouTube. After fitting them they worked perfectly and the lever was back to normal with a lower biting point and no more slipping.

But after a while the problem began again and I can't think why, I fitted them correctly as per the Cafelat video on YouTube, am I missing something?

Seriously thinking to try the Londinium rubber seals instead. Has anyone tried the current seals ?


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Trevor Watters

The simplest answer is "Yes, they work very well".

Reiss Gunson

hi martin

i assume you're talking about the L1(2012-16), so i have moved the post into the relevant section as the LR is an evolution of your machine, whereas the machine now sold as an L1 is quite different to your machine

if pre-infusing using boiler pressure it is easy to grind too fine + dose too high + tamp too hard

when you do this the puck acts like a mud brick house and becomes almost impermeable to water pushing down on it at boiler pressure

im not sure how dark a roast you are running

if it is more towards medium than dark you can turn the boiler pressure up as far as the sirai will allow, which is about 1.45 bar - stab the steam wand before you pull the lever to force the red light on to ensure you are pulling the lever with max pressure in the boiler (this is not relevant to the LR)

grind more coarsely, dose less, tamp lighter and i think you will find the 'problem' goes away

also wait for the first drip to fall in the cup before releasing the lever - this indicates that the puck is at or near saturation

let us know how you get on

kind regards

reiss.

Martin ismail

Hi Reise

Yes it is the older L1 and my roast preference is medium to dark but never oily. So I adjusted the sirai to 1.45 and without changing my grind and dose I pulled the first shot, to my surprise the lever's biting point began much lower than before. I'll adjust the grind a little coarser tomorrow and see how that goes but your theory worked straight away thanks very much Reise...


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Reiss Gunson

its really quite straight forward:

liquids are non-compressible, so once the puck is saturated during pre-infusion when you release the lever the piston is driven down by the expanding spring, which in turn pushes the water below the piston but above the shower screen down through the shower screen to the puck below

if the puck is saturated and liquids are non-compressible then it is a case of one in, one out

i.e. for the piston to be able to push 1mL of water into a saturated puck 1mL of water has to be driven out of the bottom of the puck

however, if the puck is not saturated and contains dry areas within it then when the spring drives the piston down the water below the piston does not meet the non compressible liquid in the saturated puck; instead it discovers that there is air between the grounds of coffee and so this water just 'disappears' into these air spaces instead of meeting the resistance of the water between the coffee grounds, and you see the lever arm fly up and not much coffee come out the bottom and incorrectly describe this 'piston slip'

the only slipping that can occur is the seal groove is 5/16" high and the standard seals are 7mm and so when the spring forces the piston down the seals can be pushed upwards in the seal groove by the difference in height (5/16"-7mm), and for that reason our high performance seals are 5/16" in height, perfectly matching the height of the seal groove and thereby eliminating any possibility of the seal slipping

best

reiss.

Reiss Gunson

ps - when lever machines were developed everyone was drinking dark (italian) roasts with a dose of around 14g and ground relatively coarsely and so this issue doesn't really occur

today with modern super light nordic roasts that demand a large dose, perhaps as high as 23g, lots of heat, and lots of brew water traditional lever machines that pre-infuse at boiler pressure simply cant cope

that is why we developed the L1/2/3 range with elevated pre-infusion pressure, and then off the back of that developed the L1(2012-16) further to create the LR, which in essence mimics the design of the L1/2/3 but with the convenience of plug and play that a tank fed machine provides

by varying the pre-infusion pressure on any of our current range you can have an optimised extraction for any roast profile

reiss.

Matthew Hoffman

I run the boiler pressure in my L1 (2012-2016) at 1.2 bar, with 15g pucks containing medium-light to medium roast coffees. When I have trouble saturating the grinds fully, I let the lever rise to the catch point and hold it there until the spring pressure fully saturates the puck. I fear that if I raised the boiler pressure any higher, the brew water would become too hot. (I use the new Londinium seals and never see slippage.)

Matt

Martin ismail

Thank you guys for your input. It certainly makes sense when explained in a scientific manner... I'll keep the cafelat seals until they need changing then I'll use Londinium seals.


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