Hi everyone,

Recently I've been having several problems with my Andreja and think that one of them is the OPV. Two weeks ago the machine started making a weird high frequency noise when the brew pressure goes up to around 9 bars. I know that the OPV is set to 9.5bar so I'm guessing that the noise is simply generated by the opening valve, as the machine goes silent again after a few seconds. Could that be it?

In addition usually during a shot the stream coming out of the PF (not a naked one but with the spouts removed) is pulsating from around the 15s of the extraction until the very end. It starts quite slow, dripping and forming a thin 'tail', but when it gets thicker a bit it simply starts flowing inconsistently like it was choking or spitting out the coffee. Could that also be somehow connected with the 'faulty' OPV? Maybe the spring inside is a bit worn out or there's not enough lubrication, so the whole thing simply jams slightly while dropping below 9bars and going above it again.

On top of that all (like it wasn't enough:)) I was curious whether using the OPV to restrict brew pressure is really the way to go. Factory setting for the OPV is 12bars as most of you know, and this is for both cheaper and more expensive machines (pro HB ones). I know that the companies that produce those machines, at least the more HB oriented, are aware that most users turn them down to 8.5-9bars, although they still leave them set to 12 bars when they leave the factory. Have you ever wondered why they do that? I mean maybe the OPV is not supposed to be used for brew pressure regulations? A friend of mine was doing some tests that involved sticking a pressure gauge in a HX installation and came to a conclusion that the OPV is mainly used to release pressure build up when the water left in the tubes is heated and pressure raises. The OPV opens so that your machine is not blown up to pieces by that heated water. I started thinking about his discovery (which is pretty obvious) and wondered what would happen if I was to turn the OPV up to 12 bars again and control brew pressure simply by grind. When the pressure is too low, change the grinder setting to finer, when it's too high switch to a coarser grind. This of course complicates the whole routine, as you have temperature, pressure and volume to look at and I was curious whether it's possible to achieve an optimum of some sort to get 9bars of pressure, 60ml of espresso from a double basket, brewed at 90*C or so. The last thing is easy to achieve with the use of cooling flushes. Volume is also quite easy to achieve on it's own, but because it is connected with grind settings and that is connected with pressure, it gets a bit harder. I mean is it at all possible to set a grind setting which would give you 60ml of liquid brewed at 9bars without touching the OPV? I'm pretty sure it depends on the coffee (freshness, type) but even if that element is spot on, it might be a tricky task. You can always play with the dose changing that to further affect the output but that complicates things further. I thought of this method which might make it possible, although it can cause channeling with lower doses or higher pressure:

- turn your OPV up to 12bars
- dose normally, tamp, lock and brew checking the brew pressure and volume
- if brew pressure is above 9bars, grind coarser and check volume again
- if volume is too high compensate by dosing a bit more, so the flow is slower (although this might push the pressure a bit up)
- if volume is too low, dose less

You might need to correct your grind settings after changing the dose.

I'm curious if you can achieve anything drinkable with that kind of approach. Anyone ever tried something like this?

Cheers,
dsc.

Try adjusting the valve down to a much lower pressure- like around 7 or 8 bars, grind accordingly, and see how the machine reacts to that. Maybe even disassemble the valve to be sure that it is not caked with hard water deposits or other debris that could be affecting its operation. Examine the piston or sealing area (I do not know that machine) for signs of wear or corrosion, etc.

I would question the accuracy of your friend's gage. 12 bar is high and I do not think that you would find that many machines all set that high. Fooling the OPV would be difficult because the resistance to the flow of water can change during the extraction. That is just a guess. Also remember that if you are comparing the machine's gage which is plumbed to the internal pressures to the one mounted to a portafilter, you are measuring two different pressures.

The OPV would not (should not) be opened by internal pressures when the machine is idling. The simple heating of water in the boiler will not create the pressure that you get from the pump.

My Andreja started making exactly the same noise 3 months after I bought it. I brought it back to the shop twice and was told twice that my machine was ok and nothing was wrong with it. My machine still makes that noise and I'm now trying to convince myself that it's normal... I respoke to the seller and he offered me to come back and make some coffee with them to show them how the machine really behaves since they don't seem to find the problem.

I'm wondering if anybody I's going to find a solution...

Hi,

I will definitely disassemble the valve today to see what's going on. I'm pretty sure the noise is caused by the OPV, but I'm more concerned about the pulsating flow than the noise.

As for the pressure build up you would be amazed, but it does get to pretty high values. The additional manometer (which shows the build up) is installed in the HX. Pump pressure is not the only cause of OPV activation.

Cheers,
dsc.

dsc wrote:(...) This of course complicates the whole routine, as you have temperature, pressure and volume to look at and I was curious whether it's possible to achieve an optimum of some sort to get 9bars of pressure, 60ml of espresso from a double basket, brewed at 90*C or so. The last thing is easy to achieve with the use of cooling flushes. Volume is also quite easy to achieve on it's own, but because it is connected with grind settings and that is connected with pressure, it gets a bit harder. I mean is it at all possible to set a grind setting which would give you 60ml of liquid brewed at 9bars without touching the OPV? I'm pretty sure it depends on the coffee (freshness, type) but even if that element is spot on, it might be a tricky task. (...)

I really like this question! In my limited experience with it, a grind/dose that 'naturally' produces ~9 bar flows really quickly... I can't remember anything about the taste though... Something to play with this weekend!

Your question also reminded me of this thread

Henry

dsc wrote:.... I mean is it at all possible to set a grind setting which would give you 60ml of liquid brewed at 9bars without touching the OPV?

Let's say you add the requirement that the extraction takes 25 seconds (approx. 2.4 ml/sec, ignoring the water absorbed by the coffee).

As I see it, without an OPV you can use the grind setting to control the pressure (9 bar) or the flow (2.4 ml/sec). But not both.

For a given voltage, the pump is going to discharge a specific flow at a specific pressure. For instance, the curve for the common Ulka vibe pump shows a discharge of around 4.3 ml/sec at 9 bar. So if this is the pump you have in your machine, and you want to extract 60 ml in 25 seconds, then your OPV will have to shunt the excess flow (1.9 ml/sec in this example) back to the reservoir.

In this particular example, the correct OPV setting would be the one that shunts exactly 1.9 ml/sec at 9 bar. And this is probably not exactly the same OPV setting that shunts 4.3 ml/sec at 9 bar, which generally means your so-called static pressure reading with a blind filter should be higher than the desired brew pressure.

To avoid the need for adjusting the OPV, and to control both the pressure and the flow using your grind setting only, then you must have a means of altering the basic pump discharge curve. For a vibe pump like the Ulka, this probably means controlling the voltage.

Jim

The OPV on my Anita also squeaks a bit. This seems to be a common problem with the OPV used in Quickmill machines. See this video of pulling a shot. The pump noise is totally drowned out by the squeaking OPV.
I just spent the last couple of days readjusting the OPV to try to get rid of the annoying squeal. After tuning it up from 8 bars to 9 bars, the squeal is almost gone. Now it squeaks just a bit when it comes up to full pressure, then the machine is almost silent. Much more pleasant.

As for the pressure variations, I would expect those to have more to do with distribution problems than the OPV. But I'm not sure.

Hi,

well first test are not promising. I turned the OPV up to 12bars and no matter how I grind the coffee the OPV still activates.

Jim: yes that's all true but if you add a restriction in form of coffee the flow is lowered isn't it? Otherwise even with the OPV opening at 9bars you wouldn't be able to get a ristretto because it would flow with 2.4ml/s and I believe a ristretto is much slower (well at least at the start).

Beezer: that's exactly the sound I was getting until today when I took the OPV apart, cleaned it in some lemon juice (had no citric acid) and put it back together (lubricating the ends of the spring with some silicone grease).

Anyway I'm curious if anyone else tries it.

Cheers,
dsc.

dsc wrote:Jim: yes that's all true but if you add a restriction in form of coffee the flow is lowered isn't it?

Total flow is not lowered, just the part that goes through the coffee.

With an OPV set at ~9 bar, the total flow leaving the pump probably stays about the same regardless of the coffee resistance. But as you grind finer and/or dose more, then a larger fraction of the flow gets shunted back to the reservoir, leaving a smaller flow to go through the coffee.

With no OPV, the total pump flow drops as a result of the pressure increasing, which moves you "up" on the pump curve. You can adjust grind/dose to move anywhere you like along the pump curve -- but you gotta stay on the curve.

dsc wrote:Otherwise even with the OPV opening at 9bars you wouldn't be able to get a ristretto because it would flow with 2.4ml/s and I believe a ristretto is much slower (well at least at the start).

You still get a ristretto because more flow is being shunted through the OPV and back to the reservoir. Total flow might still be around 4.3, but now only 1.2 ml/sec (for example) goes through the puck, while the remaining 3.1 ml/sec goes back through the OPV to the reservoir.

Jim

Beezer wrote:I just spent the last couple of days readjusting the OPV to try to get rid of the annoying squeal.

An OPV should not squeal. 15 minutes and a dollop of Lubrifilm is all it takes to make it silent.

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