Hi there,
I am writing to you with a request for proper pressure adjustment in machines with vibration pump. I know that this topic was answered many times but I made some measurements and my results doesn't coincide with "proper" results about which I've read.

I am an happy owner of Bezzera Magica with vibration pump. I saw YouTube video where Mr Bezzera tells that correct pressure gauge indication on blind basket should be 11 bars. But on the other hand, there are flow rates recommendations for vibration pumps, that say that they should drain 2 to 2,5 ounces of water in 25 seconds - if they are set around 9 bars of pressure (also on blind basket). That range of flow rates I achieved when built-in pressure gauge shows around 13B...

I've also checked my results using home-made pressure gauge test in portafilter. I've adjusted the flow by untightening the screws connecting PF and gauge so they could "leak" about 1,5 ounce of water in 25 s. With machine built-in gauge set to 13B - PF gauge showed about 12B - which is way too much (but the measured flow rates where OK). I had to drop the pressure in machine gauge to about 10B to achieve 9B at PF - but in such a case flow rates were way too much.

When machine pressure gauge shows around 11B (according to Mr Bezzera recommendations) I get 10.5B at PF gauge and of course flow rates bigger than recommended (around 4 oz in 25 s.).

In some YouTube video from Whole Latte Love they showed that they achieved proper flow rates (1 ounce of water in 13s) when built-in gauge showed 10B.

So as you can see I am confused. So - what is the proper way of pressure adjustment? Should I stick to flow rates or just set it around 11B and forget?


Greetings,
Kasper from Poland.

General guidelines is 10 bar with a blind filter in which should give you 9-9.5 bar in the coffee puck




Randy

Kasper wrote:So as you can see I am confused. So - what is the proper way of pressure adjustment? Should I stick to flow rates or just set it around 11B and forget?

If Bezzera says to set your OPV to 11 bar with the blind filter, I'd suggest trying 11 Bar. From there, adjust your grinder to achieve your 25 second espresso. If it really seems to you that you need to adjust the OPV down, then do so AFTER trying to dial it in at the suggested OPV setting, first. Changing more than one variable without brewing a a half dozen coffees in between will only give misleading results.
If you can make your machine produce good results on the factory settings, that's a good place to stay.

slipchuck wrote:General guidelines is 10 bar with a blind filter in which should give you 9-9.5 bar in the coffee puck

Randy

This is generally correct. WIth a blind filter in start by adjusting pressure so it is roughly one bar higher than what your target is. If that is to have the E61 "standard" 9bar at the puck then about 10 bar with the blind filter should get you there with a well prepped and properly ground puck. There is no reason thought that you can't set it for 9bar with a blind filter which will give you 8bar at the puck. Lots of people see improvements while brewing lower than 9 bar. Like ALL lever machine users.

Any ideas why my flow rate at 10B is much higher than 2oz per 25 s?

If the pump is working fine and the OPV is set at 10 bar with the blind filter in place; the flow rate is dependent upon how fine the coffee is ground and the dose (how much coffee is in the portafilter basket). Are you grinding your own beans or using pre ground beans? If grinding your own beans: focus on the grind and keep the dose constant. If using pre ground beans: adjust the dose (more coffee if flow is too fast, less if too slow).

cafe102 wrote:If the pump is working fine and the OPV is set at 10 bar with the blind filter in place; the flow rate is dependent upon how fine the coffee is ground and the dose (how much coffee is in the portafilter basket).

I'm talking about flow rate measured with blind basket on.

http://www.youtube.com/watch?v=kEl-uNOC1P4

PS - As you can hopefully understand my question is quite technically advanced (I hope) so please don't ask me if I am using pre ground coffee...

/downloads/ ... models.pdf

If you're not getting more than somewhere above 2 ml/s at brew pressure, you may have problems with extraction. These Ulka pumps seem to have a lifespan of 3-10 years in light, home use in an E61 box. They can potentially be rebuilt, or replaced for around US$30-50. There are several models within a given "series", as noted in the spec sheet above. More Watts isn't a more powerful pump. Within a given series, the ones with the higher duty cycle are, in my opinion, better choices if available at a reasonable price.

Edit: Looking at the Ulka specs, with 2 ml/s being 120 cc/min, while it should able to comfortably achieve 2 ml/s against 9 bar of pressure, it looks to be right at the edge of the spec at 11 bar.

Personally, I ran my E61 at around 9 bar blind pressure. There's nothing magical about 9 bar of extraction pressure. Lever aficionados and owners of machines where the pressure can be managed routinely extract in the 5-8 bar range (so, perhaps a 6-9 bar blind-pressure indication).

Edit: Remember also that gauges of the price class typically used are, at best, 5% of full scale devices, when new. That's around 0.75 bar on a 15-bar gauge.

Kasper wrote:I'm talking about flow rate measured with blind basket on.
...

There is no flow rate with a blind filter on, just pressure.

Flow rate is the amount of liquid output over a given period of time.

With a vibe pump at a fixed maximum pressure (9 bar, 10 bar, 8 bar...} that will ultimately be determined by the depth, density and integrity of the puck.

Adjust yout OPV with a blind basket in place to roughly 1 bar higher than the pump pressure you desire and then produce an excellent quality puck.

Other than that, as Jeff said, you may have a bad pump.

OP seems to be measuring flow rate out of the OPV with a blind basket in place. This seems to be a controlled way to measure available flow for extraction at that pressure.