Commercial lever group extraction pressures

#1: Post by **Chert** » July 27th, 2013, 9:45 am

Thanks to erics I have a setup for measuring pressures in a portafilter.

I connected it this morning to my Astoria style lever to which I have previously added an inner spring. With the lever in the down position I read 140 psi (9.65 bar according to a google search) and as I open the needle valve the pressure gradually declines from there.

Anyone have any pressure readings from other commercial lever groups? Now that I have two springs on both groups I'm curious to know what the standard group peak pressure reads but I don't want to remove a spring to find out.

Skol,

Flint

BTW Velton's Guatemala ASUVIM Atitlan was very tasty after my pressure tests brought the group up to good extraction temperature in record time (Astoria 17 grams - 1.75 oz over 26 sec)

#2: Post by **allon** » July 27th, 2013, 9:51 am

Iirc it's around 6-7 bar. I can try to remember to bring my group pressure gauge home from work and measure for you.

July 27th, 2013, 3:27 pm

What's the setup look like? I'd be curious to measure all my levers now that all but the S10 have new springs..

July 27th, 2013, 7:51 pm

Me, too.

When I bought my Quickmill Achille from Chris Coffee, they said pulled at 11 bar, but I have no independent verification of that.

#5: Post by **another_jim** » July 27th, 2013, 8:23 pm

I read approximately 10 to 7 bar on the Strega with cruder measuring gear. Since that is also a double spring Astoria, the results are compatible.

I've read from a few sources that there are two main spring choices, each with with or without the auxiliary spring; so you can get anything from 6 to 10 bar initial pressure by mixing and matching. The same spring choices are available on the Bosco style groups, since they are apparently made by the same supplier.

#6: Post by **cafebmw** » July 27th, 2013, 11:38 pm

1954 gaggia exportazione (spagna) with new springs and seals all 3 groups show 9-10 bar. same on my home machine 1973 gaggia orione.

July 29th, 2013, 12:08 am

Thanks for posting about the spring group pressures.

Here is the setup I have since you asked, Tom.

Tom@Steve'sEspresso wrote:What's the setup look like? I'd be curious to measure all my levers now that all but the S10 have new springs..

Erics has more information. One can check maximum pressure with the needle valve closed and open it to a variable degree to mimic the flow of a shot.

It requires me to remove the drip trays to fit it under the group for testing.

#8: Post by **drgary** » July 29th, 2013, 12:42 am

Rick Bond tested his Conti Prestina with a newly installed spring and got about 5 bar. However with the Prestina you can push the lever to assist the spring. So far I like the quality of shots I'm getting. Jim tried my machine and considered it "mellow" and also cited the lower end of pressure. Here's Rick's description in more detail:

rick_bond wrote:I've scace'd a fair few commercial lever groups recently and I am always surprised by the variation in maximum pressure achieved during the shot, due of course to the specifications and setup of the spring. The first serious restoration I completed was of an old Bo-Ema machine made in Australia, which used a group similar to the early CMA groups. I ordered some new springs from a local supplier, and spring pressure in use was bang on 9 bar at it's peak and tapered down from there. The shots I had from that machine were some of the best I've had, ever.

During the early stages of working on the Conti I ordered a new spring from Monaco amongst the other parts I needed. What I've found in testing thus far is that even with the new spring I am hitting a max. pressure into a very restricted outflow of around 5 bar. I am in the next few weeks going to seek out a spring winder to see if I can have them fabricate a second inner spring to complement the main spring. I dont think there is much room to increase the thickness of the main spring, as I've tried a 6 mm spacer and it's now very close to binding, with only a slight increase in max. pressure.

So far the coffee has been good in that it's more or less viceless and mellow, but it's lacking the defining characteristics when compared to pump machines.

#9: Post by **Carneiro** » July 29th, 2013, 6:24 am

Gaggia old lever group: after I've installed the spring it was reaching almost 10 bar, later it dropped, as the spring deformed a little bit:

But it was very hard to start a shot at 9 bar. In general, with my method to expel the air (delay of the PF lock-in) and a long pre-infusion I could get it starting around 8 bar.

#10: Post by **vberch** » July 29th, 2013, 10:11 am

Marcio, could you please elaborate on how you insert the portafilter?

I do this on my Cremina. I lift the lever half way up and insert the portafilter. I tried it on my Faema Lambro but didn't see the bite point on the lever change, so I assumed it accomplishes nothing.

I would greatly appreciate your feedback.

Carneiro wrote:Gaggia old lever group: after I've installed the spring it was reaching almost 10 bar, later it dropped, as the spring deformed a little bit:

But it was very hard to start a shot at 9 bar. In general, with my method to expel the air (delay of the PF lock-in) and a long pre-infusion I could get it starting around 8 bar.