There's been a number of posts puzzling about how to adjust the pressure on vibe pump HX machines (and some high end single boiler machines). Here are some instructions which will work provided you have an adjustable overpressure valve. If you don't, you'll have to dissassemble it and modify the spring -- check for Greg Scace's posts on this, it's beyond my competence.
The maximum pressure on vibe pumps is regulated by the overpressure valve. Most people like this to be set between 9 to 10 bar, while most machines come with it set to 11 or 12 bar, hence the adjustment instructions.
These valves come in various shapes and sizes, but they are always in the same place in the water circuit (see diagram), and always have a hose teed off going back to the tank or into the drip tray. If it goes into the drip tray, reroute it to the tank, since there will be a lot more flow once you adjust it down (the lower the max pressure, the more flow you get back into the tank)
Some models have a barrel with an adjustment screw, on others, the barrel with the hose back to the tank rotates for adjustment. Clockwise (screwing in) is more pressure, anti-clockwise (screwing out) is less pressure.
If you have a pressure sensor panel mounted, use it while running the pump with a blind filter to make the adjustment. If you have a pressure sensing PF, use it while adjusting (it blocks the pumpflow). Now here's the new one, you can approximately set these things without a pressure guage. Vibe pumps drain 2 to 2.5 ounces of water in 25 seconds when they are at 8.5 to 9.5 bar. So put in a blind filter, use a measuring cup to catch the run off back to the tank, and adjust it to get that flow rate (wait for the pressure to max before measuring, you'll hear this in the pump going quiet as the flow stops, it'll take up to 10 seconds for preinfusing ones).
To get more crema, but also more bitters and sours, set it to a higher pressure (less flow); to get less crema, but smoother taste, set it for more lower pressure (more flow). Those measuring flow can make these tuning adjustments by measuring the flow prior to adjusting, then tweaking in the direction they desire.
At higher pressure the espresso tastes more bitter because the finer grind results in over extraction. But why is there more sour taste at higher pressure?
The difference is subtle, but it seems to me that both bitter and sour components extract more, while the buffering sweet and oily components don't. However, other people have tasted it different, and I shouldn't have written that portion without this disclaimer. Thanks for letting me make it.
My advice, as always, is to experiment and find the pressure that suits you best.
A few months back, I lowered the pressure on my machine to between 9-9.75 depending on whether or not the heating element was on during the pull and didn't notice much difference in taste compared to the standard, delivered stock pressure.
However, after reading some of your earlier posts about prefering to do the pressure around 8-8.5, I adjusted my pressure down as well. This resulted in a MARKEDLY smoother shot, with a less harsh bite and a nicer aftertaste.
I've not gone back since and am much happier with overall shot quality.
Posted Sat Apr 17, 2004, 8:54am Subject: Re: Adjusting vibe pump pressure on HX machines
Thanks for the info Jim. Maybe another reason why the ElektraMicroCasa a Leva (~8bars) pulls a smoother shot with less crema than the Tea (~8.75bars) using the same batch of beans.
Noel Mano dell 'operatore> Macinadosatore> Miscela> Macchina espresso
jim_schulman Senior Member Joined: 19 Dec 2001 Posts: 3,772 Location: Chicago Expertise: I live coffee
Posted Sat Apr 17, 2004, 11:25am Subject: Re: Adjusting vibe pump pressure on HX machines
narc Said:
Thanks for the info Jim. Maybe another reason why the ElektraMicroCasa a Leva (~8bars) pulls a smoother shot with less crema than the Tea (~8.75bars) using the same batch of beans.
The spring levers apparently start at higher pressure, when the spring is compressed, and end at lower pressure, when the spring is expanded.
I tried aping the effect by plugging the Tea into the variac and dropping voltage during the shot. It improved longer shots with a lighter colored finish, but didn't do much for ristrettos. I tried the 3 cup test, 1/3 of the shot in each cup, and with the pressure drop, the final 1/3rd (the usually nasty light stuff) had no bitterness.
After the SCAA, I'll see if I can get together with Joel and do some side by sides. I also have a vibration snubber, but it's 1/4 npt, and I need conversion fitting to mate it to the pump line.
Posted Sat Apr 17, 2004, 2:06pm Subject: Re: Adjusting vibe pump pressure on HX machines
It's beginning to sound like the dream machine not only has perfect temp stability with the ability to set a desired temp but also a controled ramp down of extraction pressure. Also with the ability to set a pressure profile.
Noel Mano dell 'operatore> Macinadosatore> Miscela> Macchina espresso
jim_schulman Senior Member Joined: 19 Dec 2001 Posts: 3,772 Location: Chicago Expertise: I live coffee
Posted Sat Apr 17, 2004, 4:14pm Subject: Re: Adjusting vibe pump pressure on HX machines
narc Said:
It's beginning to sound like the dream machine not only has perfect temp stability with the ability to set a desired temp but also a controled ramp down of extraction pressure. Also with the ability to set a pressure profile.
I've become fairly convinced, based on my better shots, that excessive sourness and bitterness in espresso, as opposed to regular brew, is probably due to poor machine settings and extractions. I've been pulling some very bright single origin coffees, and quite frequently get superb results, wonderfully concentrated, but without any harsh edge at all.
Problem is I'm not sure what the recipe for this is. Espresso machines were developed to make very nice cups out of the very low grade coffees available in Italy in the late 40s through early 60s (mainly bottom grade Brazils and East Africans). Blends have been upgrading ever since, and roasts have been getting lighter and more fragrant. But I'm not sure if the machine tuning has fully kept up. My feel is that there's a lot of gold left to be mined in traditional espresso machine design
dcbrown Senior Member Joined: 13 Jan 2004 Posts: 167 Location: Chicago Expertise: I love coffee
Espresso: PID Zaffiro Grinder: Innova i1d
Posted Sat Apr 17, 2004, 6:45pm Subject: Re: Adjusting vibe pump pressure on HX machines
One thing to keep in mind is that pressure gages are notoriously inaccurate. The pressure reading that works best for somebody else's might not work best for you.
I adjusted my machine down from 11 bar to about 9.5 and saw a dramatic improvement. When I brought it all the way down to 9.0 the shot quality suffered. I've since turned it back up a bit and the color and taste of my shots is much better.
Use your gage as a general guide, but then listen to your taste buds.
jim_schulman Senior Member Joined: 19 Dec 2001 Posts: 3,772 Location: Chicago Expertise: I live coffee
Posted Sat Apr 17, 2004, 8:24pm Subject: Re: Adjusting vibe pump pressure on HX machines
dcbrown Said:
One thing to keep in mind is that pressure gages are notoriously inaccurate. The pressure reading that works best for somebody else's might not work best for you.
I adjusted my machine down from 11 bar to about 9.5 and saw a dramatic improvement. When I brought it all the way down to 9.0 the shot quality suffered. I've since turned it back up a bit and the color and taste of my shots is much better.
Use your gage as a general guide, but then listen to your taste buds.
Absolutely, taste is king. In any case, either my spring on the valve or the gauge is very non-linear, since it took a lot more turns to go from 10 to 9 than from 11 to 10 bar.
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