Are flow control espresso machines worth the added cost? - Page 2

Recommendations for buyers and upgraders from the site's members.
Nunas
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#11: Post by Nunas »

I don't get this... when fully open, should it not be the same pressure as the pump? Maybe my misunderstanding is that I am confusing flow with pressure???
Don't feel bad...took me a while to figure this thing out. You're on the right track though; flow and pressure control are related.

A standard mushroom has a jet with a tiny hole. With no portafilter, you can switch it on and measure how much water comes out in a given time. The pressure with no coffee involved will be near zero. But the pump will still be showing 9-bar (nominal). With a blind basket in the PF, the pressure will ramp up fairly quickly to 9-bar, once the preinfusion chamber is filled. With too coarse coffee, the pressure will be low and the flow will be high. With too fine coffee, the inverse, right up to a choked shot (which is really just like a blind basket).

Now, with the flow control, the jet is no longer there. In its place, you have a needle valve. Turned down it is off. The pump will measure 9 and there will be no pressure to the PF and no or nearly no flow. With the needle valve wide open, water will VERY quickly fill the preinfusion chamber (fraction of a second) and the valve will shoot up (you can hear it). You get 9-bar pressure to the puck nearly instantly, depending on the grind (as above).

Assuming a reasonable espresso grind, with the standard spring and the valve open only slightly, the pump will show 9-bar, but the needle valve will only allow a trickle of flow. The e61 head gauge will very slowly ramp up as the preinfusion chamber fills very slowly. You can probably have up to a minute of preinfusion (I've never measured). Once it is full, you will see the pressure rise more rapidly to its maximum (9-bar for a good grind). However, if the valve is too closed, you may not get to the full 9-bar. This is because, once the e61 inbuilt preinfusion is over, you then have full control of flow/pressure by using the valve. Open about 1.5 turns and the needle valve opening is about the same aperture as the stock e61 jet. You'll then get standard e61 preinfusion. The kit comes with a gauge so you can see this easily. It's really great fun to play with if you're at all an "experimenter" with your espresso.
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pcrussell50
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#12: Post by pcrussell50 »

This is a great synopsis for E61 type machines.

For modded GS/3 and modded BDB, you don't have a pre infusion chamber to fill. So it is just direct control right from the beginning as soon as you turn on the pump.

-Peter
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millmountain
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#13: Post by millmountain »

Nunas wrote:Don't feel bad...took me a while to figure this thing out. You're on the right track though; flow and pressure control are related.
To the explanation of Nunas I would just add that, as far as I've understood, pressure profiling is done at the pump. That is, in those types of machines, changes in flow of the water to the group/basket follow as a response to a change in pressure created at the pump. In flow profiling, pressure is created at the basket in response to the restriction of water flow.

For the electrically inclined, this is analogous to voltage, current and resistance, with pressure akin to voltage, current like flow and then of course resistance. The pump creates "voltage." Current only flows where there is a path. The pipes, valves, nozzles (gicleur = nozzle) and other pathways create resistance to flow/current. The main resistances to flow in the flow-profiling machine are the "needle valve" (don't know the proper term, the part controlled by the user) and, if present, the puck. The puck has a mostly constant resistance, reducing only slightly over the shot. The user-operated needle can change its resistance on the fly. By increasing its resistance during a shot, less water flows, and since the resistance of the puck hasn't changed much, less pressure gets built up above the puck where the pressure gauge is located. (That's why the pump pressure still reads full pressure while the group-head pressure varies.) If you remove the extra resistance to flow at the needle, only the puck resists pressure and so you get the "full" (only reduced by the normal resistance to flow) pressure. In the electrical analogy, pressure profiling works by varying the "voltage" at the source, i.e., the pump, and the rest of the circuit is passive, that is, it doesn't change and flow just results from the pump pressure and the condition of the puck.

Don't know if that makes sense to anyone else.

Nunas
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#14: Post by Nunas »

This is a great synopsis for E61 type machines. For modded GS/3 and modded BDB, you don't have a pre-infusion chamber to fill. So it is just direct control right from the beginning as soon as you turn on the pump.
Thanks, Peter. I should have mentioned the spring change, which I alluded to earlier. On an e61, when installing the flow kit, if one changes out the spring (which I understand is similar to the Bianca spring), this effectively eliminates the inbuilt e61 preinfusion function. So, the needle valve operates similarly to what you describe for the GS/3. Personally, I like it better with the old spring. But with the new spring, it's more intuitive.

Jonk
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#15: Post by Jonk »

Flow/pressure profiling can be very useful for medium/dark roasts as well. When it comes to the E61 kits the cost is fairly low, absolutely worth it.

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slybarman
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#16: Post by slybarman »

thecruz831 wrote:Good Morning all!
I am looking to upgrade my Rancilio Silvia to a new machine and have been reading a lot about flow control machines. At first I was looking at a Rocket but now machines like the Lelit and ECM models with flow control are looking good.

I guess my question is the value add really worth it?

Thanks in advance!
Funny you asked, I was thinking about posting my $.02 on this the other day. I had ZERO interest in flow control before getting a new machine. I thought it was gimmicky and one more variable added to the equation that I was opposed to having to deal with. I bought a Lelit Bianca because I got a slamming deal on a second-hand unit. I bought the machine IN SPITE of having flow control. I have had the machine for about 8 or 9 months now and eventually started to dabble with the flow control. I will say I changed my mind about it. I do think it can be useful. I think I have been able to get better shots from beans that were too fresh for instance by way of controlling the flow/pressure ramp up. I think I have also been able to get more sweetness and less bitterness out of other beans. It can be complicated in terms of understanding what profile to use when. I have been referencing a basic guide that Dalla Corte put out that I think is generally useful.

As others have said, there is no real downside to having it and you can dabble with it as wanted/needed over time.

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Peppersass
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#17: Post by Peppersass »

Nunas wrote: Now, with the flow control, the jet is no longer there. In its place, you have a needle valve. Turned down it is off. The pump will measure 9 and there will be no pressure to the PF and no or nearly no flow. With the needle valve wide open, water will VERY quickly fill the preinfusion chamber (fraction of a second) and the valve will shoot up (you can hear it). You get 9-bar pressure to the puck nearly instantly, depending on the grind (as above).
Are you sure the jet is no longer there? Seems to me that if there's no flow restrictor other than the needle valve in, say, a Slayer, the puck would get slammed when you pull a shot without "pre-brew" (i.e., needle valve bypassed for a shot with traditional ramp/pressure profile.)

I don't believe that's the case. In pre-brew mode when the basket has filled it gets to 9 BAR almost instantly because the pump always runs at the speed required to produce 9 BAR at peak with or without the needle valve and the pre-brew time is set so that the needle valve is bypassed just as 9 BAR has been reached. The flow restictor opening is larger than the needle valve opening, so it doesn't add any ramp time. It does, however, slightly reduce the pressure at the puck (versus pressure at the boiler) after the basket fills because the puck is permeable -- i.e., the path isn't completely sealed and water is flowing through it.

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bluesman
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#18: Post by bluesman »

millmountain wrote:By increasing its resistance during a shot, less water flows, and since the resistance of the puck hasn't changed much, less pressure gets built up above the puck where the pressure gauge is located. (That's why the pump pressure still reads full pressure while the group-head pressure varies.) If you remove the extra resistance to flow at the needle, only the puck resists pressure and so you get the "full" (only reduced by the normal resistance to flow) pressure.
That's not exactly correct. Pressure is force per unit area, e.g. pounds per square inch. And because liquid is incompressible, the pressure of a liquid is the same throughout and in all directions. Fluid at a pressure of 10 psi will exert a force of 10 pounds on the blind end of a tube with a 1 square inch cross section. If you cut the size of the tube to 1/10 of a square inch, the force exerted on whatever's closing off its end will only be one pound - but the pressure is still 10 psi.

Along with force, the other important factor here is volume flow per time unit, which (unlike pressure) is controlled by the cross sectional area of the narrowest point in the fluid path, along with several less significant (to us) parameters like resistance of the walls of the conduit to flow and flow patterns within the path (eg laminar, turbulent, etc). Once the critical area of the path is reduced below that which will pass the full volume of the pump's output at the specified rate, the volume of water per second drops as does the maximum force it can exert on whatever's in its way (which is the puck in this case).

I'm pretty sure that's how these needle valves affect the process. They reduce the force with which the brew water hits the puck and they reduce the volume flow. But this all happens at the same pressure unless the pump can't maintain it against the restriction, which is not likely to happen with the kinds of machines we're discussing.

EDIT: Having said all this, I just reread the descriptive literature on these kits, and they do say that the pressure is reduced. I don't understand how this is possible unless the needle valve is so tight that the brew path is almost completely closed or there's a bypass somewhere in the new mushroom that bleeds some of the pressurized brew water out of the brew path. Anybody have more input?

Nunas
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#19: Post by Nunas »

Are you sure the jet is no longer there? Seems to me that if there's no flow restrictor other than the needle valve in, say, a Slayer, the puck would get slammed when you pull a shot without "pre-brew" (i.e., needle valve bypassed for a shot with traditional ramp/pressure profile.)
I must admit that I've have not taken it apart to see if there's both a needle valve and a jet. However, if there is a jet, the orifice in it is huge. When one opens the needle valve fully then engages the pump, the preinfusion rod slams audibly and the group pressure goes to pump pressure very quickly.

Nunas
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#20: Post by Nunas »

EDIT: Having said all this, I just reread the descriptive literature on these kits, and they do say that the pressure is reduced. I don't understand how this is possible unless the needle valve is so tight that the brew path is almost completely closed or there's a bypass somewhere in the new mushroom that bleeds some of the pressurized brew water out of the brew path. Anybody have more input?
With the needle valve fully closed, there's virtually no flow and there's no bypass that I can detect. I'm reasonably certain that this kit is nothing more than a modified jet, into which an adjustable tapered shaft can be moved (i.e., a needle valve). If you look at the original e61 patent diagram you can see it there. I've no idea why or when the needle valve was eliminated, but I'm glad it's back :lol: .