E61 Flow Control Device and pressure

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#1: Post by Arafel »

So I've read a lot lately about pressure and flow and how they are interrelated. I know with something like a Strada, you can truly control pressure with the pump. I currently have a Pro 600 with FCD, and I've noticed that when I do long preinfusions, at some point the pressure rises to 9 bar no matter what, so it seems like with the E61, flow and pressure aren't really tied together. Has anyone noticed this? Anyone have any insight on how pressure works with an E61?

Also, with the Slayer, does the preinfusion stage truly limit pressure, or it like an E61 FCD where at some point you end up at 9 bars?


#2: Post by bakafish »

Arafel wrote:I've noticed that when I do long preinfusions, at some point the pressure rises to 9 bar
It means your FCD doesn't limit the flow rate low enough or you grind too fine and choke the machine. What is the lowest flow rate of your machine without the portafilter?


#3: Post by Pressino »

Arafel is correct in that the e61 FCD is basically a throttling valve that controls FLOW rate and indirectly under specific parameters & circumstances can control pressure. With a pump that operates at a fixed pressure you cam throttle the valve as close to fully closed as you want but if the outflow offers sufficient resistance (up to and including complete blockage) eventually you will reach fullpump pressure in the brew chamber. The only way to control brew pressure within those parameters mentioned above is to have a variable pressure pump driving water through the brew chamber.

This does not mean that the throttling e61 FCD isuseless. It is extremely useful in espresso extraction, but you need to work within its limitations.


#4: Post by mycatsnameisbernie »

Arafel wrote:when I do long preinfusions, at some point the pressure rises to 9 bar no matter what
Can you adjust your FCD so that it completely stops the flow of water? If so, you should be able to limit pressure for pre-infusion. It takes a bit of hand-eye coordination to do it right. Once the pressure starts to rise, it's easy for it to get carried away, but you can always slow it down by completely closing the FCD valve.


#5: Post by BeesKnees »

If it is a vibe pump, it should follow this curve + whatever your machine is doing to the flow/pressure.

So many of the pumps have a fast flow at low bars.


#6: Post by Pflunz »

That is only partially right.
Yes, flow is larger at small pressure, but the pressure the pump sees with a flow control in the water path will always bei the pressure set by the OPV (with a portafilter and well grinded coffee in place).
The flow at the pump pressure will then by divided into flow through OPV and flow to the group. When you further close the needle valve, pump pressure and pump flow will stay the same, but the OPV/group flow ratio ist changed in a way, that more water will flow through the OPV.