Has anyone gotten a satisfactory shot at 9 bar on Breville BES900XL without adjusting the OPV?

#1: Post by **ScottS986** » February 10th, 2014, 12:33 pm

Hello,

I own a Breville BDB BES900XL, one of the 2nd gen ones where they updated the OPV. With a blind disc I show 10.5 bar on the gauge. I can make delicious shots (32-37s, 18g beans, 36g shot weight, fresh beans) but they will always register between 10 and 10.5 bar on the gauge. If I grind/dose/tamp the shot so it flows at 9 bar, it will be way too fast and underextracted.

I've experimented with opening the hot water tap slightly to get a 9 bar flow, and I do believe that it tastes smooth with better mouthfeel. I'd like to be able to pull nice 9 bar shots (without needing to do pressure bleed from the hot water tap)

What to do? Even if I had the OPV adjusted to kick in at 9 bar, it would kick in every time. It seems I ought to be able to pull a shot at the right pressure w/o the OPV needing to kick in to limit the pressure every time?

Any suggestions much appreciated!

Thanks,
Scott

#2: Post by **cuppajoe** » February 11th, 2014, 10:49 pm

Mine behaves much the same except it stops at 10 consistently. The coffee's good, which is what matters. Have been playing a bit with the different controls, just to see how they effect things. Have only had it a little over a month and am happy with it.

It's been educational to see what impact pre infusion has. Have only been at this since last April/May.

#3: Post by HB » February 12th, 2014, 10:06 am

ScottS986 wrote:It seems I ought to be able to pull a shot at the right pressure w/o the OPV needing to kick in to limit the pressure every time?

But that's how over-pressure valves work for vibratory pumps. I still don't get it: Why adjust the OPV? elaborates on this point.

#4: Post by **cmin** » February 12th, 2014, 10:28 am

ScottS986 wrote:Hello,

I own a Breville BDB BES900XL, one of the 2nd gen ones where they updated the OPV. With a blind disc I show 10.5 bar on the gauge. I can make delicious shots (32-37s, 18g beans, 36g shot weight, fresh beans) but they will always register between 10 and 10.5 bar on the gauge. If I grind/dose/tamp the shot so it flows at 9 bar, it will be way too fast and underextracted.

I've experimented with opening the hot water tap slightly to get a 9 bar flow, and I do believe that it tastes smooth with better mouthfeel. I'd like to be able to pull nice 9 bar shots (without needing to do pressure bleed from the hot water tap)

What to do? Even if I had the OPV adjusted to kick in at 9 bar, it would kick in every time. It seems I ought to be able to pull a shot at the right pressure w/o the OPV needing to kick in to limit the pressure every time?

Any suggestions much appreciated!

Thanks,
Scott

Like HB said that's how an opv operates, however you can adjust them to bring it down (when the BDB first shipped some had out of wack opv settings and either had the machine replaced or fixed themselves which is easy). Just open it up and adjust the opv down to 9-9.5 and see what happens.

here's some steps with pics
http://nic.steve-tek.com/?page_id=180

February 13th, 2014, 5:21 pm

Thank you for the responses. I'm sure that you may be somewhat tired of this topic, so I really do appreciate the insight. The thing is I have read, and re-read, and re-re-read the threads on the OPV you suggested and still don't feel like I have a clear answer.

I get that you can regulate the max pressure on a vibe pump with an OPV and that this is a simple approach to ensuring good pressure, especially for singles and ristrettos, but I'm just asking about doubles here.

I also see discussion that an OPV is not a necessity on all vibe pump machines to get good shots (Elektra Semiautomatic for ex.)

So is the conclusion that on some vibe pump machines (but not all) the only way you will be able to get a good 9 bar shots is to use the OPV?

Lastly, I've tried to use that Ulka pump curve graph to figure out this answer. I get that at 9 bar, I would get 3.67oz flow in 25 seconds. I know that some water is absorbed into the coffee. So, is the conclusion there that it is clearly not possible to get a good "in range" shot at 9 bar w/o OPV, or that all this adds up somehow and it's possible.

Many thanks,
Scott

#6: Post by HB » February 13th, 2014, 6:09 pm

I was tempted to ask why you don't simply adjust the OPV and move on, but I'll play along...

One can work out the math, or measure the actual pressure under flow rates with or without an OPV. Based on the chart below, a Ulka E5 puts out 200 cc / minute @ approximately 10 bar. So, if the total extraction time is say 25 seconds, it's at full pressure for maybe 20 seconds, less if it has preinfusion engaged. There's also some fudge factor for puck absorption prior to full pressurization and post full pressurization. For sake of argument, let's say there's 20 seconds of full pressurization time; if so, maximum flow @ 10 bar would be ((200 cc / min) * (1/3 min)), or around 66 cc. Depending on the particular pump, the pressure will be higher or lower, as indicated by the dotted line range shown below. That doesn't sound too far off reality.

All charts and math aside, I've measured non-OPV espresso machines like the Elektra Semiautomatica and the brew pressure is around 10 bar at double flow rates, around 11 bar at ristretto flow rates.

But don't take my word for it, try it yourself. To really get an idea of what's affected, bracket the results with a good delta between each set. For example, try the brew pressure at 7 bar, 9 bar, and 11 bar for a few days each and then narrow in on the one you prefer. Typically the lower pressure settings will channel less, but crema production will suffer and the taste may go flat. At higher pressures, crema production peaks, but the risk of channeling increases and the taste may go bitter/acrid.

February 14th, 2014, 3:04 pm

Dan, that really helped. Thank you. I think I'm getting it now. This morning I weighed my portafilter before and after extraction. Ignoring whatever dissolved coffee went into the cup, it weighed 37g more, so let's say there was 37cc of water in there. So in your example, at 10 bar, after my preinfuse, if there was 22s of full pressure, that would be 73cc of water in 25 seconds. Subtract the 37cc left in the PF, that leaves 36cc in the cup, which sounds exactly like my shot this morning, which did flow at mostly 10 bar.

So my takeaway here is that a good 10ish bar shot on this pump is no problem, but a 9 bar shot would be pretty difficult to achieve without the OPV.

#8: Post by **cuppajoe** » February 14th, 2014, 9:10 pm

Have seen no obvious signs of channeling so far. Pre-infusion is set so pressure very gradually ramps to 1 bar, then the pump kicks in for the shot. Don't remember exactly what the pre-infusion parameters are, but can get back with them later if you want.

The puck sticks once in awhile, but a quick punch on one of the buttons kicks it off the screen(into the knockbox).