I'm playing with some manual grinders and I just realized that by adjusting grind level and being meticulous about puck prep one can achieve the target brewing pressure without relying on the OPV. In my case my machine is set to not go beyond 9 bar, and I could get the target pressure of around 8.5 bar by just adjusting grind level:



In none of these cases the OPV had any work to do. Does this mean that with machines that don't have adjustable OPV (where the maximum pressure can be as high as 12 bar) users just need to be more careful about grind level adjustment and puck prep instead of bothering with aftermarket solutions?

Edit: To give you some background as to why I find this interesting, some machines are frequently recommended against because their OPV is set too high and is not adjustable. The Nuova Simonelli Oscar and Oscar 2 are such examples, and there are other entry level machines that even come with a pressure gauge and a PID, but have an OPV that's set to 11 or 12 bar and is not easily accessible (e.g. Lelit PL41TEM). My point following this experiment is that a non-adjustable OPV that's set too high might be less of an issue than commonly believed, and that users should worry less about how the OPV is set in these machines and more about getting optimal grind level and puck prep.

personally i find hitting 8.5~9 bar pressure gives most complex taste, anything less is much linear shot.
i had long adjusted my opv from 10.5 down to 9 bar. its quite a hassle on bdb so im not gonna mess it again.

i didnt pay as much attention back then, but i recall most of my shots hover around 9.5, and dropping even just a small bit of the opv down to 10 didnt do much on brew pressure, but instead had provide a significant reduction in burnt bitterness, much more than what dropping temp would do. it also doesnt go sour unlike dropping temp. you probably had experience brewing higher pressure when adjusting, maybe you can relate?

what i do find really different is that pucks are less prone to channel, and that made it much easier to prep.

i think what i cant do is when grind near choking, i cant have the machine sticks to 9bar until flow starts. generally it will bump higher then drops (suggesting possible channeling). however i dont really do this kind of ristretto since the yield is too small, usually 1:1 or less, and the dripping flow is hard to be consistent. works well on icecream tho.
i believe this might be a limit to consider.

i have preinfusion control with bdb, so i have other methods to do long bloom and finer grinds, but without it you'd probably cant do much at those grinds settings.

i was also suprised going to ssp mp was a magnitude higher of difficulty in prepping good puck, simply saying its more difficult is an understatement, even vs stock 64mm italmill. with my consistent 1zkpro shot to shot down to sec, i wasnt even nailing a single consistent shot with ssp until i start playing brew pressure and level up my puck prep.

boren wrote: In none of these cases the OPV had any work to do.

I highly doubt that. The OPV does not open at one pressure and is then open, it also has a linear area on which it starts to open.
I don't know with which machine you did your test, but if you check the pumps datasheet, you will find a table or diagram, in which you can read how much flow the pump delivers at which pressure. An Ulka E4 will be at 200ml/min and an E5 at 300ml/min, both at 8.5bar. This results in a flow of 3.3ml/s (resp. 5ml/s) for that given pressure. Without an additional valve which takes some amount of this flow and redirects it back, this will be your espresso flow. If you look at your table, there is no chance that you can have this flow for your noted ~30s and get a decent espresso. A gicleur will help to reduce this flow by increasing the pressure the pump sees, but this is not enough the restict the flow to 1-2ml/s (which equals 12 bar or 14 bar pump pressure)
If you would have used your Bianca, it would have been even worse. Rotary pumps deliver even more water, thats why they are having a valve near the pump, which transports back most of the water back to the entry of the pump. Otherwise it is not possible to get an espresso with a rotary pump.

I used my Bianca V3 for these tests, but setting grind level coarse enough to not be able to reach the OPV set pressure should be doable with any machine.

@Pflunz - where would you expect to notice a difference in shots pulled at 8.5 bar (due to grind level) on a machine with OPV set to 9 bar and then after adjusting it to 12 bar? Do you expect shot time, flow rate or resulting coffee (taste, body etc) to be any different?

boren wrote:setting grind level coarse enough to not be able to reach the OPV set pressure should be doable with any machine.

Yes, but at the cost of an huge amount of water flow, far away from typical espresso range.

boren wrote:@Pflunz - where would you expect to notice a difference in shots pulled at 8.5 bar (due to grind level) on a machine with OPV set to 9 bar and then after adjusting it to 12 bar? Do you expect shot time, flow rate or resulting coffee (taste, body etc) to be any different?

As I said, you have to check for the flow of the pump at a given pressure. I don't know any pump which delivers 1ml/s at 8.5bar. They always deliver more. Hence, when you are having a flow in the range of 1ml/s, you either have an additional water flow path (OPV or bypass valve), or the pump sees a way larger pressure (due to some flow restrictors).
The Bianca should be even more complicated, since there is the OPV you are referering to and probably one bypass valve next to the pump. EIther way, you cannot assume that

boren wrote:with machines that don't have adjustable OPV (where the maximum pressure can be as high as 12 bar) users just need to be more careful about grind level adjustment and puck prep

Those machines are inherently not able to deliver the required pressure/flow combination.

Pflunz wrote: As I said, you have to check for the flow of the pump at a given pressure. I don't know any pump which delivers 1ml/s at 8.5bar. They always deliver more. Hence, when you are having a flow in the range of 1ml/s, you either have an additional water flow path (OPV or bypass valve), or the pump sees a way larger pressure (due to some flow restrictors).

But if there's no difference in actual flow through the coffee bed or pressure in the grouphead, why does it matter what happens elsewhere in the machine? And again, where do you expect to notice a difference in the resulting coffee?

It has to be regulated somewhere in the machine. As long as you are having the right pressure and flow the espresso will taste the same, independent from the pump.
BUT, to get to this, you cannot only have the "right grind size and have prepare the puck well". There has to be a mechanism in the coffee machine to make it possible to get that flow and pressure. Typically this is the OPV. But you asked specifically for machines without OPVs. Then, if there is no other mechanism to reduce the flow for a pump, the answer is "no, it is not enough".

I think you may have misread my question. I'm not asking about a machine with no OPV, but about what happens when you adjust it to different points that are anyway beyond the actual extraction pressure.

boren wrote:@Pflunz - where would you expect to notice a difference in shots pulled at 8.5 bar (due to grind level) on a machine with OPV set to 9 bar and then after adjusting it to 12 bar? Do you expect shot time, flow rate or resulting coffee (taste, body etc) to be any different?

If in both cases the grind level doesn't allow building enough pressure to hit the OPV pressure, where would it make a difference if the OPV is set to 9 bar (0.5 bar more than extraction pressure) or 12 bar (2.5 bar more)?

BTW, I can only tell for a fact that you can get the grouphead pressure to reach 8.5 bar by adjusting grind level. I didn't measure what happens to the flow rate if in an 8.5 bar extraction I adjust the maximum pressure of the machine from 9 bar to 12. If you or anyone else here knows please share.