# Benefits of reducing pump pressure



## SteveR (Aug 21, 2017)

I've got everything I need to do it on my pre 2015 classic, and I've measured the pressure already at 14 bar. What is the benefit of reducing it to 10? Why not 11? 9.5? In other words, what am I trying to achieve by reducing the pressure, and how will I know when it's at the "correct" level, whatever that is?


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## lake_m (Feb 4, 2017)

It's taste. The beans you are using will have a sweet spot. Try reducing the pressure in stages and taste. Most machines OPV come pre-set at 9 bar so I would start here and work your way down.


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## 4085 (Nov 23, 2012)

It brings you closer to a lever shot.


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## SteveR (Aug 21, 2017)

dfk41 said:


> It brings you closer to a lever shot.


 Why is that a good thing?


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## SteveR (Aug 21, 2017)

lake_m said:


> It's taste. The beans you are using will have a sweet spot. Try reducing the pressure in stages and taste. Most machines OPV come pre-set at 9 bar so I would start here and work your way down.


It was at 14 bar, it's now at 9 after a full anticlockwise turn of the spring nut. I over adjusted the grind to compensate taken me half an hour to dial it back in, but I can't see much difference. Crema is same quantity, maybe lighter in colour. In a flat white it's a more mellow less intense flavour, not sure I like it as much....


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## lake_m (Feb 4, 2017)

SteveR said:


> It was at 14 bar, it's now at 9 after a full anticlockwise turn of the spring nut. I over adjusted the grind to compensate taken me half an hour to dial it back in, but I can't see much difference. Crema is same quantity, maybe lighter in colour. In a flat white it's a more mellow less intense flavour, not sure I like it as much....


There's your answer then.


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## MWJB (Feb 28, 2012)

SteveR said:


> It was at 14 bar, it's now at 9 after a full anticlockwise turn of the spring nut. I over adjusted the grind to compensate taken me half an hour to dial it back in, but I can't see much difference. Crema is same quantity, maybe lighter in colour. In a flat white it's a more mellow less intense flavour, not sure I like it as much....


How have you adjusted the pump pressure? If you have just adjusted the over pressure safety valve, how has this changed the pressure at the puck?


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## 4085 (Nov 23, 2012)

Simple, a lever extracts from spring pressure so once you release it then it exerts say 6 bar which falls away as the spring returns. A pump excerpts the same pressure from start to finish and is usually higher. Simple explanation by the way


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## MediumRoastSteam (Jul 7, 2015)

SteveR said:


> It was at 14 bar, it's now at 9 after a full anticlockwise turn of the spring nut. I over adjusted the grind to compensate taken me half an hour to dial it back in, but I can't see much difference. Crema is same quantity, maybe lighter in colour. In a flat white it's a more mellow less intense flavour, not sure I like it as much....


When I had my classic, I found the sweet spot, for me, to be at 10.5 bars. When I adjusted to 9, I found pretty much the same as you are saying. Give it a go, see how it works for you and go from there.


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## MediumRoastSteam (Jul 7, 2015)

MWJB said:


> How have you adjusted the pump pressure? If you have just adjusted the over pressure safety valve, how has this changed the pressure at the puck?


That's how it works in a Gaggia Classic. You can measure the pressure at the group with a manometer connected to the PF.


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## MWJB (Feb 28, 2012)

MediumRoastSteam said:


> That's how it works in a Gaggia Classic. You can measure the pressure at the group with a manometer connected to the PF.


But if water is exiting through the OPV at over 9bar, how do you know what the pressure is at the puck? Surely you just know that the OPV sees 9bar+, then opens, some pressure is released via the OPV & some through the puck?


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## SteveR (Aug 21, 2017)

MediumRoastSteam said:


> When I had my classic, I found the sweet spot, for me, to be at 10.5 bars. When I adjusted to 9, I found pretty much the same as you are saying. Give it a go, see how it works for you and go from there.


Thanks I'll try that. I only turned it 360 degrees rather than the 1+1/4 turn that most you tubers suggest. There was a fair bit of leakage with the pressure gauge fitted, so it's likely my 9 bar reading was less than the true value. I was also caffeined out by this time, as it took about 4 shots to dial the grind back in!


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## MediumRoastSteam (Jul 7, 2015)

But if you have a pressure gauge mounted at the portafilter (like a scace device) isn't that measuring the pressure hitting the PF? That's how everyone else does it.


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## SteveR (Aug 21, 2017)

MWJB said:


> But if water is exiting through the OPV at over 9bar, how do you know what the pressure is at the puck? Surely you just know that the OPV sees 9bar+, then opens, some pressure is released via the OPV & some through the puck?


You don't measure at the opv, you measure in the PF. The absolute value isn't really important, it's the change from factory setting that's important. A pressure gauge screwed onto the bottom if the PF is probably sufficiently accurate, given how many other variables there are in the coffee making process.


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## SteveR (Aug 21, 2017)

dfk41 said:


> Simple, a lever extracts from spring pressure so once you release it then it exerts say 6 bar which falls away as the spring returns. A pump excerpts the same pressure from start to finish and is usually higher. Simple explanation by the way


OK, but why is emulating a lever a "good thing"?


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## MWJB (Feb 28, 2012)

MediumRoastSteam said:


> But if you have a pressure gauge mounted at the portafilter (like a scace device) isn't that measuring the pressure hitting the PF? That's how everyone else does it.


Scace has an aperture to emulate a puck.


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## MediumRoastSteam (Jul 7, 2015)

MWJB said:


> Scace has an aperture to emulate a puck.


So, all I am saying is that without the aperture, a 10 - 10.5 bar reading works for me and for most of the Classic owners who opt to do the OPV mod. That's all.


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## 4085 (Nov 23, 2012)

That is a rhetorical question and one I cannot answer using an iPhone. Should be home in a couple of days but am sure some else will chip in


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## SteveR (Aug 21, 2017)

MediumRoastSteam said:


> So, all I am saying is that without the aperture, a 10 - 10.5 bar reading works for me and for most of the Classic owners who opt to do the OPV mod. That's all.


Exactly, so long as you're making consistent measurements then you have a process to set up your machine. Since most of us use a manometer attached to the PF we can compare the data as we're using the same method, which is sufficiently accurate to achieve the desired machine setting. We're not really concerned with the true pressure values at the opv, merely the inferred measurement at the PF.


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## SteveR (Aug 21, 2017)

SteveR said:


> Exactly, so long as you're making consistent measurements then you have a process to set up your machine. Since most of us use a manometer attached to the PF we can compare the data as we're using the same method, which is sufficiently accurate to achieve the desired machine setting. We're not really concerned with the true pressure values at the opv, merely the inferred measurement at the PF.


So a few hours later, I turned it back a quarter turn, just ground some beans for three doppios and kaboom! Ker-pow! The taste is back and better than before. Perfect for me, until I change beans supplier next week, but that's for another day.

No idea what the pressure is, for some reason my PF leaks everywhere with the manometer attached (yet doesn't with a blanking plate, how does that work then?), so I get no reading of any meaning from it. Who cares, coffee tastes great.


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## lake_m (Feb 4, 2017)

SteveR said:


> So a few hours later, I turned it back a quarter turn, just ground some beans for three doppios and kaboom! Ker-pow! The taste is back and better than before. Perfect for me, until I change beans supplier next week, but that's for another day.
> 
> No idea what the pressure is, for some reason my PF leaks everywhere with the manometer attached (yet doesn't with a blanking plate, how does that work then?), so I get no reading of any meaning from it. Who cares, coffee tastes great.


Classic error which I did myself. Take the basket out of the portafilter. It's leaking from the underside of the basket under the lip - Doh!


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## SteveR (Aug 21, 2017)

lake_m said:


> Classic error which I did myself. Take the basket out of the portafilter. It's leaking from the underside of the basket under the lip - Doh!


But I left basket in!


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## MediumRoastSteam (Jul 7, 2015)

SteveR said:


> But I left basket in!


When you take the basket out, what reading do you get then?


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## SteveR (Aug 21, 2017)

MediumRoastSteam said:


> When you take the basket out, what reading do you get then?


Even less of one. I couldn't get up to 1 bar with the basket in, ouy similarly useless. It can't be at 1 bar though because it's producing coffee!


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## lake_m (Feb 4, 2017)

Read my post. Take the basket out. It can't make a seal with the basket in because the water flows back under the lip of the basket.


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## SteveR (Aug 21, 2017)

lake_m said:


> Read my post. Take the basket out. It can't make a seal with the basket in because the water flows back under the lip of the basket.


Ah ok got you. I read it that your mistake was you took the basket out! I'll try again later maybe


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## lake_m (Feb 4, 2017)

SteveR said:


> Ah ok got you. I read it that your mistake was you took the basket out! I'll try again later maybe


Without the basket fitted you'll just need to twist the portafilter further round in the group head until it seals on the bare rim. But it does seal.


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## SteveR (Aug 21, 2017)

lake_m said:


> Without the basket fitted you'll just need to twist the portafilter further round in the group head until it seals on the bare rim. But it does seal.


I thought I'd tightened it enough tbh, but clearly hadn't. What's odd us that I did this pressure test when I first got then achieved a couple of months ago, pretty sure I left the basket in then too, and had a perfect leak-free test!


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## Obnic (Jan 14, 2014)

Seal ring may be getting hard.


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## Obnic (Jan 14, 2014)

SteveR said:


> .... What is the benefit of reducing [pressure]?


I'm going to stick my neck out here (others will correct me) and say it's something like this:

Extraction yield reaches a natural peak as you grind finer; that is to say that at some point the resistance of the puck prevents water flowing through. With lower pressure, you can grind finer. I think because the pump pressure compresses the puck less. This should lead to higher extraction.

There is certainly a noticeable effect when I extract at 6bar. The shot flows much faster so I have to grind significantly finer to maintain brew time.

As for lever profiles: As an extraction progresses water flows through the puck faster so water-to-bean contact-time gets less. That's inconvenient because later in the shot the oils remaining in puck are less soluble. The benefit of a reducing pressure profile (like that of a lever) is that the rate of flow through the puck stays broadly the same throughout the shot.

Actually, ignore that, levers are the espresso equivalent of the occult. It's voodoo, alchemy. So quiet.... it's creepy. They loom there with their big arm in the air... waiting.


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## SteveR (Aug 21, 2017)

Obnic said:


> I'm going to stick my neck out here (others will correct me) and say it's something like this:
> 
> Extraction yield reaches a natural peak as you grind finer; that is to say that at some point the resistance of the puck prevents water flowing through. With lower pressure, you can grind finer. I think because the pump pressure compresses the puck less. This should lead to higher extraction.
> 
> ...


I assumed that reducing pressure requires a coarser grind to maintain the same extraction time. Those ate essentially the three variables that your trying to control, and I'm not sure which is the critical one, i.e. the one that you want to set and adjust the other two around it.


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## MediumRoastSteam (Jul 7, 2015)

SteveR said:


> I assumed that reducing pressure requires a coarser grind to maintain the same extraction time. Those ate essentially the three variables that your trying to control, and I'm not sure which is the critical one, i.e. the one that you want to set and adjust the other two around it.


I've tried it. I reduce the pump pressure on my machine to 6bar a while ago and you do indeed have to grind finer. I know it's counter intuitive, but that's confirmed. And, on the 6bar, I tried it but didn't enjoy it. With my machine (Pro-700), I prefer the taste at 9bar.


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## Obnic (Jan 14, 2014)

For me, 6bar extractions work best for lighter roasts. I use a fine grind, light tamp, long pre-infusion and then 6 bar, often to relatively high brew ratios. This can yield sweet and juicy shots. If you do this with darker roasted beans the results can be very maillard-led burnt, smokey, bleugh.


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