I just bought my 1st machine ( a Bezzera Magica still hasn't arrived) & I've been reading a lot on brew pressures & OPV's. I was concerned that the machine I bought would brew at around 9 bar & if need be the brew pressure was adjustable with an OPV adjustment, turns out Bezzera sells an adjustable OPV "kit" that would fit the Magica. I called the vendor to find out about my order & asked him if the machine had an adjustable OPV, his response was "why do want to adjust an OPV ? The OPV will not effect brew pressure only brew temp. the way to adjust brew pressure is with your grinder" My response was "OK sounds good". Now I'm confused (that didn't take long) Is the vendor correct ? I'm not sure what I'm missing. I thought brew temp was adjusted by flushing the GH to desired temp.
Thanks
Larry

The vendor's comment about the OPV affecting brew temp is odd, makes no sense at all to me. Maybe he was thinking/talking about the pStat at that point?

When he said that the way to adjust brew pressure is with your grinder, that makes sense. There is a relationship between pressure and flow rate inherent in your pump, where it goes to 12+ bar when the flow is completely choked off. See the diagram below:



In normal brewing the pressure is around 9 bar and is determined by the flow rate as permitted by the fineness of the grind.

The OPV on most machines (I'm not familiar with the Magica) opens somewhere above 9 bar, often as high as 12 bar or so.

The reason you may want an OPV that opens at a lower pressure is if you want to pull slow ristretto shots without the brew pressure going much above 9 bar. Until you are used to the machine and think your ristrettos need the lower pressure I'd say you don't need to worry about fitting an adjustable OPV.

Link wrote:I thought brew temp was adjusted by flushing the GH to desired temp.

Yes - on an HX machine the length of your cooling flush is the usual way to control your brew temp.

OPV on the magica is adjustable, from the factory they will brew at 12 bar

homeburrero wrote: Yes - on an HX machine the length of your cooling flush is the usual way to control your brew temp.

Close, but not quite.
The boiler pressure ultimately controls the brew temp.
The flush helps set the starting brew temperature. HX machines display a characteristic hump in brew temperature.

Every HX machine will be a little different though - with a small boiler, the flush may be more significant. With a large boiler, less so. The efficiency of the heat exchange design will also be a significant factor - surface area, volume, thermosyphon, etc.

The most important thing is to pay attention to how your machine works and take into account that advice from other people is tuned to their experience. It may not be directly applicable to your specific machine, though with interpretation it may be helpful.

Good luck with your journey!

homeburrero wrote:The reason you may want an OPV that opens at a lower pressure is if you want to pull slow ristretto shots without the brew pressure going much above 9 bar. Until you are used to the machine and think your ristrettos need the lower pressure I'd say you don't need to worry about fitting an adjustable OPV.

Yes I agree I need to use the machine & see how it works try different grinds & techniques I've been reading about. I have a feeling it's going to take a few weeks of trial & error until I get a grasp on how and why I'm getting good/bad shots. I would think a company such as Bezzera would make a home machine that would work very well right out of the box especially for a beginner. So I take it that if OPV is set at 12 bar the initial brew pressure will start out around 12 bar & then decrease as the grind/dose will then determine brew pressure and that pressure will show up on the gauge. The vendor defiantly was saying OPV maybe thinking pstat ?

4000ft wrote:OPV on the magica is adjustable, from the factory they will brew at 12 bar

That's good to know especially when spending that kind of money the machine should be able to handle something that seems so important to the HB community. I'm really surprised the vendor asked me why I'd want an adjustable OPV when the manufacture is building them that way, I guess they won't be much help with questions down the road. I took his advice on a grinder and now I'm having second thoughts on that.

Thanks for the reply's
Larry

Link wrote: So I take it that if OPV is set at 12 bar the initial brew pressure will start out around 12 bar & then decrease as the grind/dose will then determine brew pressure and that pressure will show up on the gauge.

No, if your grind is right you will see the pressure ramp up to ~9 bar and never get to 12 bar. When you put a blind basket in and backflush, then you will see it ramp up to 12 bar. If you grind really fine and pull a 35 second shot with only 15-25g of liquid, you will see it reach a high pressure, maybe 12 bar. If you like these ristrettos you can adjust the OPV down to where it limits the pressure on slow-flowing shots and see if you like that even better.


12 bar factory setting is what you get on the ECM/Rocket machines as well. I suspect that must be what works best for most users.

allon wrote:The boiler pressure ultimately controls the brew temp.

Agree with that. The pStat setting is the one that puts the machine in the right range. The cooling flush, and how you go about it (flush-n-wait, flush-n-go, don't flush) is how you tweak the temp for a particular pull.

No, if your grind is right you will see the pressure ramp up to ~9 bar and never get to 12 bar. When you put a blind basket in and backflush, then you will see it ramp up to 12 bar. If you grind really fine and pull a 35 second shot with only 15-25g of liquid, you will see it reach a high pressure, maybe 12 bar. If you like these ristrettos you can adjust the OPV down to where it limits the pressure on slow-flowing shots and see if you like that even better.


Got it. Thanks for clearing that up for me.

A good idea would be to go to the Bezzera site - http://www.bezzera.it/index.php?lang=en and download the parts manual for the Magica AND their accessories catalog.

The reason these machines have their OPV set to such a high value (11-12 bar) is that the ESE Pod specification requires same. Keep in mind that these machines are sold all over the world and some countries are, perhaps, greater ESE Pod users than others. In the accessories catalog (last page), Bezzera lists a "kit" to convert certain models to 9 bar OPV capability - the Magica is not one of them but perhaps things have changed. I do realize the Magica OPV is adjustable but taking it to 9 bar may be out of the design range of their spring.

Here is an better drawing of the Ulka performance curve:



There exists a goodly share of posts as regards OPV adjustment - see the Resources Section of this site. The bottom line is that adjusting the OPV to 9, 10, 11, or 12 bar with a blind filter in place sets the MAXIMUM pressure you will ever see.

erics wrote:The reason these machines have their OPV set to such a high value (11-12 bar) is that the ESE Pod specification requires same.

Thanks Eric - that makes total sense, I'd never heard that before. Is comforting to know that the downside of diverging from the factory setting involves something I don't ever use.

erics wrote:A good idea would be to go to the Bezzera site - http://www.bezzera.it/index.php?lang=en and download the parts manual for the Magica AND their accessories catalog.

The reason these machines have their OPV set to such a high value (11-12 bar) is that the ESE Pod specification requires same. Keep in mind that these machines are sold all over the world and some countries are, perhaps, greater ESE Pod users than others. In the accessories catalog (last page), Bezzera lists a "kit" to convert certain models to 9 bar OPV capability - the Magica is not one of them but perhaps things have changed. I do realize the Magica OPV is adjustable but taking it to 9 bar may be out of the design range of their spring.

Here is an better drawing of the Ulka performance curve:

<image>

There exists a goodly share of posts as regards OPV adjustment - see the Resources Section of this site. The bottom line is that adjusting the OPV to 9, 10, 11, or 12 bar with a blind filter in place sets the MAXIMUM pressure you will ever see.

Thanks again for your help, & the ese pod info. I did check out the Bezzera site but just found out today my Magica is on a slow boat from Italy so the Vendor is shipping me a Rocket Cellini Premium Plus V2. UPS says the machine will be at my house on 1/14 YEAH ! Not sure which machine is "better" but with me at the helm it's not going to matter !