Espresso machine design - pump activation


New member
Jul 26, 2021
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Hi all, I'm designing a home espresso machine centered around an E61 grouphead. One thing I haven't wrapped my head around yet is how temperature and pressure is maintained while pulling a shot.

My question is: Assuming a single boiler setup (not sure if this is different for a double boiler though), when a shot is being pulled, if the pump needs to be activated to maintain the 9 bar of pressure in the system, does that not just pump cold water into the system, and rapidly drop the temperature of the water going to the puck thereby affecting extraction?

Any help is appreciated, still in the learning phase of the project.


Well-known member
Aug 15, 2005
Central North Carolina
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Yes it certainly can happen, but most machines are built to pretty much offset that. Larger boiler(s) equal more thermal mass/less heat loss during the extraction. Some have a type of ring heater/coil in the group to keep things consistent there regardless of what takes place leading up to it. Some machines have smaller boilers, but a fill tube of sorts that diverts incoming water so much temperature isn't lost as it flows to the group from the hottest part of the boiler.

A double boiler can still have slight issues if the boiler is small, extractions are done repeatedly before recovery smooths things out, etc. A dialed in true single boiler can be just as good as a typical double boiler, just that the single boiler has to ramp up for steam if needed, whereas the 2nd boiler in a double boiler is always ready when you need it. Then you also have a heat exchange design, which is quite a bit different altogether...