With reference to recent posts on availability of Robot piston seals, and cost of
freight from Hong Kong, it is probably worth noting that these seals are the same as those used in modern
spring lever machines such as Astoria, Brasilia, Bosco, Kees VDW and Londinium.

It might be fruitful to widen a search for seals beyond Robot specific suppliers, to other suppliers focussed on these other machines.

The following video explains how the seals are the same as for these other machines. It is also provides a demonstration of the proper technique for removing the seal which is also applicable to the Robot. http://www.youtube.com/watch?v=MbHiIr3GCMs

I got the Robot a few days ago. Coming from a modded BDB and GCP, I was frustrated with the dial in. Initially, I was aiming for 2bar PI and low (6bar) and slow pull but ending up with thin and sour shots. Time and time again, I tightened the grind (Niche) only to end up with minimally improved results. Water was just off boil.

Today, I loosened the grind back to what I've been using on my 6.5bar GCP and skipped the 2bar PI, going straight to a 6-7bar shot. The results were night and day with thick texture and improved balance. I then pulled a blend with a more traditional roast, and it was even better.

Anyone else have trouble with the low pressure PI? Maybe some other factor I haven't taken into account?

My beans are very traditional blends and I always give it a pretty generous pre-infusion, no problems unless the roast is off.

Similarly I've never really had an issue with the PI, even when I've gone up to 30 seconds of pre-infusion. However I've only really used medium or dark roasts - are you using a light roast by any chance?

On top of that I've also never used any beans older than a 6 week roast date (thankfully we're blessed with several excellent roasters nearby).

gabeholloway wrote:I got the Robot a few days ago. Coming from a modded BDB and GCP, I was frustrated with the dial in. Initially, I was aiming for 2bar PI and low (6bar) and slow pull but ending up with thin and sour shots. Time and time again, I tightened the grind (Niche) only to end up with minimally improved results. Water was just off boil.

Today, I loosened the grind back to what I've been using on my 6.5bar GCP and skipped the 2bar PI, going straight to a 6-7bar shot. The results were night and day with thick texture and improved balance. I then pulled a blend with a more traditional roast, and it was even better.

Anyone else have trouble with the low pressure PI? Maybe some other factor I haven't taken into account?

Yes, there are other factors ...

I'm using Flair and for several years I used no preinfusion profiles because results with PI were unpredictable to me. After buying a good grinder and modifying the badly designed basket (which isn't an issue in your case), I started experimenting with PI more seriously, as most members here seem to be using it. Results are better than before, some of them somewhat better than No PI shots, some still worse ... Problem is, there are infinite number of ways how you can do it - from constant pressure lever-machine type PI to constant flow Slayer machine type PI (you can simulate all of them with Robot or Flair), and it depends when you end preinfusion and start raising the pressure and how fast. After a number of measurements I still don't have clear answers which changes are affecting the taste which way and what is the best way even with the same type of coffee, so if someone says to you he is doing x bar PI lasting y seconds, you can get totally different results if you try the same, but slightly different way

However, with some confidence, but still with limited number of samples, I can say that prolonging preinfusion after coffee starts dripping from the basket too long tends to produce more sourness - on my particular machine and particular coffee - not necessarily true on any other combination (although Slayer manual is also suggesting not overdoing it). So recently I tend to end PI and raise the force/pressure immediately after I see coffee appearing at the bottom of the basket and number of sour shots decreased significantly - with this coffee at least

In short - try finding what is working best for you and stick to it - even slight modification can change it (to worse usually)

With pump machine, it's easier to get repeatable results - with same dose and grind, it will pump the water same way every time ... not the case here

I always preinfuse but the length varies depending on coffee. 10 seconds is probably about the max often less. I also always preheat the portafilter on top of the kettle since that is "free" but I only do more extensive preheating on light roasts. I find PI improves shot quality and consistency but of course you have to be sure you are doing the PI in a consistent way. Practice makes perfect and all that

I grind pretty fine and do a long pre-infusion...the risk in my experience is astringency in the cup if I go too long. If you are getting sour I'd guess that your temp is dropping too low for your roast. I do pre-heat the basket, shower screen, and portafilter over my 1950s oven's pilot lights so they are hot to the touch.

Yes... consistency does make a difference with pre infusion! Something that is important is the speed in which you get to your desired pi pressure. I have been going for 2 bars and if I go from 0 to 2 immediately it could take nearly 20 seconds before 1st drop with the grind I use. If I ramp up slowly, like 2 to 3 seconds to get to that 2 bar, with the same grind, first drops could be as quick as 5 to 8 seconds.

First I noticed this was after watching a slayer video where it showed a pre infusion technique by quickly going to 5 bars and releasing pressure back down to 2 for the remainder of the pi. When I tried it l I could barely squeeze anything through the basket for the grind that worked well otherwise.

What I still need to experiment with is grinding coarser along with the quick pressure to see how it compares, but ever since consistently going for 2 bars gently in 2 seconds my pi is very repeatable.